Download Blueprint of Life

BIO2: Blueprint of Life
1.
Evidence of evolution suggests that the mechanisms of inheritance,
accompanied by selection, allow change over many generations
OUTLINE THE IMPACT ON THE EVOLUTION OF PLANTS AND ANIMALS OF:
- CHANGES IN PHYSICAL CONDITIONS IN THE ENVIRONMENT
- CHANGES IN CHEMICAL CONDITIONS IN THE ENVIRONMENT
- COMPETITION FOR RESOURCES
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Physical conditions: temperature, aridity
o The Australia landmass has become drier over time and this has lead to changes in the species of
kangaroos that are present today. Approximately 25 million years ago, Australia was considerably
wetter than today with large areas of rainforest. During this time, kangaroos were small and
omnivorous, with unspecialised teeth, eating a variety of foods from the forest floor.
o As Australia became more arid and grass became the dominant vegetation in some areas,
environmental selective pressure resulted in larger kangaroos favouring teeth suitable for grass. These
teeth, high-crested molars, efficiently grind low-nutrition grass into a more easily digestible paste.
Slicing pre-molars are of little use and so became much reduced from the ancestral kangaroos.
Chemical conditions: water salinity
o Chemicals, such as dieldrin and organophosphates, have been used extensively to control the sheep
blowfly. However, genetic resistance has occurred within the fly population that has made these
chemicals ineffective. Continued use of the insecticide has resulted in the mutation of a modifier gene
that increases and maintains the resistance.
Competition for resources: introduction of a new predator
o The myxoma virus was introduced in 1950 in an attempt to control the numbers of European rabbits in
Australia
 Virus is carried by fleas, and causes myxomatosis in rabbits
o At first, 99% of infected rabbits died. Over time, the death rate reduced to 50%.
o Those rabbits that survived the first infection had a greater resistance to the disease than other rabbits.
These resistant rabbits would have offspring which would inherit the resistance, so the proportion of
rabbits with resistance to the myxoma virus increased over time.
ANALYSE INFORMATION FROM SECONDARY SOURCES TO PREPARE A CASE STUDY TO SHOW HOW AN
ENVIRONMENTAL CHANGE CAN LEAD TO CHANGES IN A SPECIES
Physical change: Peppered moths in England
 In unpolluted forests, pale moths are well
camouflaged on pale, lichen-covered tree trunks
o Birds that prey on moths eat more of the
conspicuous dark moths because they are
more visible, so pale moths survive and
reproduce, and come to dominate the gene
pool
 In polluted forests near industrial cities, where tree
trunks are blackened, dark moths have a higher survival rate in the polluted environment, and so have become
dominant.
Chemical change:
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In subsequent sprayings of DDT to kill mosquitoes, low concentrations were ineffective
Few mosquitoes which survived the first spraying had a natural resistance to DDT and passed this on to their
offspring
o Population changed from mainly susceptible to mainly resistant due to selection by DDT in the
environment
DESCRIBE, USING SPECIFIC EXAMPLES, HOW THE THEORY OF EVOLUTION IS SUPPORTED BY THE FOLLOWING AREAS
OF STUDY:
- PALAEONTOLOGY, INCLUDING FOSSILS THAT HAVE BEEN CONSIDERED AS TRANSITIONAL FORMS
- BIOGEOGRAPHY
- COMPARATIVE EMBRYOLOGY
- COMPARATIVE ANATOMY
- BIOCHEMISTRY
Palaeontology: the study of fossils (including transitional forms)
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Shows sequential change, e.g. the horse
Transitional forms are examples of organisms that indicate the
development of one group of organisms from another, or from a
common ancestor
o Help us understand how evolutionary change may have
come about
E.g. Crossopterygian
o Like fish: scales, fins, gills
o Like amphibians: lobe-fins (to walk on land), lungs
o It is thought that amphibians developed from such fish that could absorb oxygen from the air
E.g. Archaeopteryx
o Like reptiles: long tail, claws, no keel, solid bones, teeth
o Like birds: wish-bone, feathers
o This flying dinosaur from the late Jurassic supports
the theory that birds developed from reptiles
Biogeography: the study of distribution of living things
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Animals and plants of Asia and Australia are very different,
separated by Wallace’s Line or Lydekker’s Line
o Australia’s unique mammals and angiosperms result
from periods of evolution in isolation
o Looking at pattern of distribution of an organism,
plus its fossil distribution, we can reconstruct its
evolutionary history
E.g. Waratahs
o Genus Embothrium grows in forests of South America
o Genus Oreocallis grow in New Guinea, north-eastern
Australia, Peru and Ecuador
o Genus Telopea grow in eastern Australia
 Present-day distribution of these closely related species suggests that western part of South
America and eastern parts of Australia may have once been connected
 Biogeography provides evidence of divergent evolution
Comparative Embryology: the study of embryos of different organisms, looking for similarities and differences
between them
 Similarity between embryos of different vertebrate species suggests a common ancestry
 E.g. All chordates possess pharyngeal gill pouches during development
o Only in fish/amphibian larvae do these develop into gills
o We probably inherited them from an aquatic ancestor
 E.g. basic vertebrate pattern of six pairs of aortic arches is modified during later development in different
vertebrates
o Adult fish has circulation pattern similar to basic pattern
o In frogs and humans, several aortic arches are lost with loss of functional gills and development of lungs
for gas exchange
 E.g. all terrestrial vertebrates have embryonic tails, even humans
Comparative Anatomy: the study of differences and similarities in structure between different organisms
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Structures in common are evidence of similar inherited characteristics from common ancestors
Structural homology e.g. the pentadactyl limb [one DotPoint down]
o Most land vertebrates show same pentadactyl (five-digits) limb pattern in arm and leg bones
o Mammalian forelimbs are said to be ‘homologous structures’
 Note*:Analogous structures have similar functions but are not necessarily similar in basic
structure, e.g. a fly’s wings and a bat’s wings
o In bats, the limb is modified to form a wing with the fingers extended and skin stretched between each
finger. Whales have within their single paddle-like fin a fully formed pentadactyl limb.
o Inherited this from aquatic ancestors, the lobe-finned fish
E.g. xylem
o Ferns, conifers and flowering plants all have vascular tissue, including xylem which transport water
throughout the plant
o Suggests that these groups of plants had a common ancestor
Biochemistry:
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Degree of similarity in molecules among a wide range of animals reflects genetic closeness
Proteins (haemoglobin), DNA, RNA and hormones are studied
Agglutination studies: Artificial antihuman antibodies are made. The serum is used to test for human proteins in
various organisms, as antibodies will cause proteins to be precipitated from solution
o Closely related animals have a small antigen-antibody reaction
o Antihuman antibodies cause 97% of chimpanzee proteins to precipitate, suggesting 97% common
proteins between humans and chimpanzees
Protein sequencing: The amino acid sequence of the enzyme ‘cytochrome c’ can be compared
o This enzyme is found in most organisms as it plays a role in respiration
o More differences in amino acid sequence can be expected if two species diverged from a common
ancestor a long time ago
 Hence, ‘cytochrome c’ functions as a molecular clock to estimate the time since two species
diverged
DNA hybridisation: [two DotPoints down]
PERFORM A FIRST-HAND INVESTIGATION OR GATHER INFORMATION FROM SECONDARY SOURCES (INCLUDING
PHOTOGRAPHS/ DIAGRAMS/MODELS) TO OBSERVE, ANALYSE AND COMPARE THE STRUCTURE OF A RANGE OF
VERTEBRATE FORELIMBS
USE AVAILABLE EVIDENCE TO ANALYSE, USING A NAMED EXAMPLE, HOW ADVANCES IN
TECHNOLOGY HAVE CHANGED SCIENTIFIC THINKING ABOUT EVOLUTIONARY
RELATIONSHIPS
DNA-DNA Hybridisation: chemical hybridisation is used to compare DNA molecules from
different species
1) DNA from a species is separated into 2 strands using heat
2) Single strands formed are mixed with single strands from another species
3) Two different strands will join to form a hybrid molecule. However, not all pairs of
bases will match. A high degree of pairing will occur is two DNA sequences are
similar. Low degree of pairing will occur if two DNA sequences are very different
4) Degree of pairing can be estimated by measuring the temperature at which hybrid
strands separate. The more bonds formed, the higher the temperature needed to
separate the strands
 Species which diverged more recently
from a common ancestor will be expected to
show a higher degree of hybridisation
 Hybridisation studies show that
humans are most closely related to
chimpanzees, followed by gorillas and then
orang-utans, which were the first to diverge
from a common ancestor
EXPLAIN HOW DARWIN/WALLACE’S THEORY OF EVOLUTION BY NATURAL SELECTION AND ISOLATION ACCOUNTS
FOR DIVERGENT EVOLUTION AND CONVERGENT EVOLUTION
Evolution by natural selection:
1) In any population there are variations among individuals
2) In any generation, there are offspring that do not reach maturity and reproduce; the characteristics of these
organisms are removed from the population
3) Those organisms that survive and reproduce have favourable variations that are well adapted to that
environment
4) Favourable variations are passed on to offspring; they become more and more common in the population
Convergent evolution:
 Natural selection can result in similar adaptations in
unrelated species that live in similar environments
o The same variations are favourable due to
same selection pressures in both environments
 E.g. Seals, dolphins (mammals) and sharks
(cartilaginous fish) both live in the open ocean
o Have limbs modified as flippers, streamlined
bodies, and eat fish. Seals and dolphins, belonging to different orders of mammals, are able to stay
under water longer than most other mammals, and have thick layer of fat under skin to conserve body
heat
Divergent evolution: (a.k.a adaptive radiation)
 Isolated populations of a single species in different environments come to present different dominant variations
through evolution, as selection pressures are different
in the different environments.
 Ultimately, the two populations might be so different
that they can no longer interbreed, and hence form
new species
o E.g. Darwin described 14 species of finches on
the Galapagos and Cocos Islands
 Habitat and diets were different, and
thus they had different body sizes and
beak sizes/shapes
 On each island, the forms that had
survived were those which were most
suited to the food resources and
habitat available there
PLAN, CHOOSE EQUIPMENT OR RESOURCES AND PERFORM A FIRST-HAND INVESTIGATION TO MODEL NATURAL
SELECTION
ANALYSE INFORMATION FROM SECONDARY SOURCES ON THE HISTORICAL DEVELOPMENT OF THEORIES OF
EVOLUTION AND USE AVAILABLE EVIDENCE TO ASSESS SOCIAL AND POLITICAL INFLUENCES ON THESE
DEVELOPMENTS
Historical Developments of Theories:
 Linnaeus : Published classification system in which he classified humans and apes together
 Erasmus Darwin: First suggested that all life came from a single source
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Cuvier: Noted that in some areas rock layers were very distinct from those beneath them, and inferred that
these changes must be due to catastrophic events. Catastrophes are followed by repopulation from other areas
John Baptiste de Lamarck:
o Proposed the idea of use and disuse, and inheritance of acquired characteristics
o Inherent drive towards higher forms
o Helped make Darwin’s ideas more acceptable
Charles Lyell
o His work ‘Principles of Geology’ proposed that the gradual geological processes we observe today have
always been occurring
o This concept of uniformitarianism entailed the Earth was millions of years old, not 6000 as it was
believed
 The large time span was necessary for the feasibility of the theory of evolution
Thomas Malthus: Wrote an essay on competition for resources, arguing that overpopulation entailed a ‘struggle
for existence’
Alfred Russel Wallace: Came to same conclusions as Darwin; evolution by natural selection
Charles Darwin: Published ‘On the Origins of Species by Means of Natural Selection’
Gregor Mendel: Developed the particulate model of inheritance, the means by which natural selection could
occur
Social and Political Influences:
 Predominant view in western cultures was creationism
o Each species had been created in its present form by God in six days
o Earth is 6000 years old, and species have not changed in this time
o Humans have a special place in the world; evolution reduces humans to same level as other organisms
 Darwin’s theory of evolution was rejected by many religious people
o Idea that humans are descended from apes caused social/political outrage
o Evolution threatened the power of religious institutions that had long held political/social power
 1920s: Protestant traditionalists campaigned against antibiblical ideas of evolution
 Several states in USA banned teaching evolution in public schools
 1925 Scopes trial: A teacher was prosecuted for teaching the theory of
evolution as fact
2.
Gregor Mendel’s experiments helped advance our
knowledge of the inheritance of characteristics
OUTLINE THE EXPERIMENTS CARRIED OUT BY GREGOR MENDEL
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Mendel cross-bred tall and short plants: all the offspring were tall
He allowed all these tall offspring (F1) to self-fertilise, and found that the F2
generation consisted of tall to short plants in the ratio 3:1 (the monohybrid
ratio)
Repeated these experiments testing other characteristics of garden peas
o Round/wrinkled seed, yellow/green seed, smooth/constricted pod, yellow/green pod, violet/white
flower, tall/short stem, terminal/auxiliary flowers
DESCRIBE THE ASPECTS OF THE EXPERIMENTAL TECHNIQUES USED BY MENDEL THAT LED TO HIS SUCCESS
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Used peas, which were easily grown and produced successive generations rapidly
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Selected characteristics which had two easily identified forms
Bred each variety for 2 years to make sure that the characteristic was consistent
o Ensured pure breeding lines
Cross fertilisation was ensured by removing stamens from one of his breeding pairs (female parent) and then
pollinating it with pollen from stamens of the other of the
pair (male parent) using a brush
Self-fertilisation was ensured by covering a plant with a bag
so that only pollen from its stamen would land on its carpels
Repeated experiments many times for reliable results
Kept careful records and counted results he obtained
o Recorded the parents of each offspring
Used mathematics to rigorously analyse results
Studied one character at a time, so that the effects of each
could not be confused
DESCRIBE OUTCOMES OF MONOHYBRID CROSSES INVOLVING SIMPLE DOMINANCE USING MENDEL’S EXPLANATIONS
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Monohybrid cross: a breeding experiment that looks at the inheritance of only one characteristic
o Offspring are known as F1 or first filial generation
 Mendel cross-bred tall and short plants: all the offspring were tall
 He allowed all these tall offspring (F1) to self-fertilise, and found that the F2
generation consisted of tall to short plants in the ratio 3:1 (the monohybrid ratio)
o Parents- TT x tt
o F1- all Tt  Tt x Tt (all tall)
o F2- 1 TT : 2 Tt : 1 tt (3 tall : 1 short)
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 Each plant had two inherited factors for each trait. Plants with identical factors
were called ‘true breeding’. Plants with different factors were called ‘hybrids’
 Each factor was a discrete particle that retained its identity across generations
(challenging the blending model)
 Mendel’s 1st law, the Law of Segregation: factors for the same characteristic occur
in pairs in an individual. These pairs separate at gamete formation, so that a
gamete contains only one factor for each characteristic
 Mendel’s 2nd law, the Law of Independent Assortment: each pair of factors sorts
out independently of other pairs at gamete formation. This means that either
factor of a pair can combine with either factor of another pair
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 All gametes from the TT parent contained the T allele, and all gametes from the tt
parents contained the t allele
o Therefore, all F1 plants had the heterozygous genotype Tt
 In a gene consisting of two possible alleles, one would be dominant and the other recessive. In heterozygous
individuals, the dominant allele would be expressed
o Hence, the F1 plants with heterozygous genotype presented the dominant phenotype (tall)
 Gametes from each Tt parent of the F1 generation may have the T allele or the t allele.
o Via a Punnet square, it can be seen that the F2 generation will be approximately 25% TT, 50% Tt, and
25% tt, i.e. 75% of the F2 generation will be tall and 25% will be short.
 A test cross is when an individual with the dominant phenotype is crossed with an individual with the recessive
phenotype (and hence is homozygous recessive) to find out whether the first individual is homozygous
dominant or heterozygous.
o
o
TT x tt  all Tt
Tt x tt  1 Tt: 1 tt
DISTINGUISH BETWEEN HOMOZYGOUS AND HETEROZYGOUS GENOTYPES IN MONOHYBRID CROSSES
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Homozygous: having two identical forms (alleles) of the gene for a particular characteristic
Heterozygous: having two different forms (alleles) of the gene for a particular characteristic
o Heterozygous offspring are hybrids: offspring of two different parents
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Parents- TT x tt (homozygous dominant x homozygous recessive)
F1- all Tt  Tt x Tt (heterozygous x heterozygous)
F2- 1 TT : 2 Tt : 1 tt (1 homozygous dominant : 2 heterozygous : 1 homozygous recessive)
DISTINGUISH BETWEEN THE TERMS ALLELE AND GENE, USING EXAMPLES
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Gene: a unit of inheritance, which occurs as a
specific locus on a chromosome, corresponding to a
particular characteristic or phenotype
Allele: a member of a gene pair; alternative factors
carrying information for the same trait, but not
necessarily the same information
o Each individual has a pair of genes for each
characteristic; one allele on each of two
homologous chromosomes
E.g. “A plant heterozygous for tallness has one
allele for tallness and one for shortness. A plant homozygous for tallness has identical alleles in its gene pair”
Genotype: actual alleles an organism possesses for a characteristic
Phenotype: outward appearance of an organism; the expressed or presented traits as a result of an organism’s
genotype
EXPLAIN THE RELATIONSHIP BETWEEN DOMINANT AND RECESSIVE ALLELES AND PHENOTYPE USING EXAMPLES
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Offspring resulting from tall crossed with short plant were just as tall as the tall parents
o Mendel called this form ‘dominant’
o The other parental form not expressed in F1, he called ‘recessive’
F1 (Tt) were genetically heterozygous, but their phenotype showed only the dominant allele (T)
o The F1 which appeared tall must also have a recessive gene for shortness which was not expressed (Tt)
In an individual homozygous for a trait, the phenotype directly reflects the allele
o TT plants are tall; tt plants are short
In an individual heterozygous for a trait, the phenotype reflects only the dominant allele
o Tt plants are tall
OUTLINE THE REASONS WHY THE IMPORTANCE OF MENDEL’S WORK WAS NOT RECOGNISED UNTIL SOME TIME
AFTER IT WAS PUBLISHED
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o Mendel published the results of his work in 1866
The significance of his findings were not recognised, perhaps because he was not a well-known, high profile
member of the scientific community
Other scientists at the time studied whole organisms, while Mendel studied single characteristics
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Because he worked initially with only garden peas, it was thought that his results were not widely applicable
The attention of scientists at the time was focused on evolution and differences between species, and there was
a decline in interest in the work of breeders who were concerned with differences within species
 He presented his paper to only a few people at an insignificant, local scientific meeting, and published it in a
small obscure journal
 At the time, the processes of meiosis and mitosis were unknown
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 Darwin’s theory of evolution had been published, but Darwin could not account for the origin of variation he
observed in species
 It was not until 1900, when 3 scientists independently produced similar data, that his contribution was
recognised
 In the 20th century, biologists have been able to explain the processes of natural selection
SOLVE PROBLEMS INVOLVING MONOHYBRID CROSSES USING PUNNETT SQUARES OR OTHER APPROPRIATE
TECHNIQUES
PERFORM AN INVESTIGATION TO CONSTRUCT PEDIGREES OR FAMILY TREES, TRACE THE INHERITANCE OF SELECTED
CHARACTERISTICS AND DISCUSS THEIR CURRENT USE
PROCESS INFORMATION FROM SECONDARY SOURCES TO DESCRIBE AN EXAMPLE OF HYBRIDISATION WITHIN A
SPECIES AND EXPLAIN THE PURPOSE OF THIS HYBRIDISATION
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Plant breeders carried out systematic crosses between different varieties of one species to form hybrids that
had new combinations of desirable characteristics
Hybridisation: the crossing of different varieties of one species to produce new varieties with different
combinations of characteristics
Hybrid vigour: hybrids combine best features of their parents
o Hybrid plants are generally more vigorous and higher yielding compared to their true-breeding parents
Wheat hybridisation in Australia:
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Flour produced from Australian-grown wheats was too poor to be used for
baking bread in last 1800s
o English varieties of wheats ripened too late to survive the hot summers
o So the flour for baking bread was imported into Australia
William Farrer systematically used cross-breeding to improve bread wheat and
pasta wheat
o Prevented self-fertilisation and carried out artificial crosses
Farrer succeeded in breeding many new wheat varieties with new
characteristics including:
o Narrow leaves to reduce water loss, to survive in Australia’s dry climate
o Early ripening to suit Australia’s shorter growing season
o Improved baking quality
o Improved yield
o Resistance to a fungal disease known as bunt
Crossed an early-ripening Indian wheat with a Canadian variety that had good baking properties, then selected
one of these, and crossed it with a higher yielding variety to make the new variety ‘Federation’
o ‘Federation’ ripened early, had high yield, and was ideal for mechanical harvesting because it had a
strong short straw
3.
Chromosomal structure provides the key to inheritance
DESCRIBE THE CHEMICAL NATURE OF CHROMOSOMES AND GENES
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Each chromosome is DNA (40%) coiled around protein cores called histones (60%)
Short lengths of DNA make up genes so genes have the same chemical composition as DNA
DNA = deoxyribonucleic acid
IDENTIFY THAT DNA IS A DOUBLE-STRANDED MOLECULE TWISTED INTO A HELIX WITH EACH STRAND COMPRISED OF
A SUGAR-PHOSPHATE BACKBONE AND ATTACHED BASES – ADENINE (A), THYMINE (T), CYTOSINE (C) AND GUANINE
(G) – CONNECTED TO A COMPLEMENTARY STRAND BY PAIRING THE BASES, A-T AND G-C
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DNA is a double-stranded helical molecule, made of subunits called nucleotides
Each nucleotide consists of a sugar(deoxyribose), a phosphate, and a nitrogenous base
4 nucleotides possible
Adenine joins to thymine and guanine joins to cytosine
Information is stored in the sequencing of bases (A,G,T,C) along the DNA molecule.
Backbone of the structure is comprised of deoxyribose sugar and phosphate molecules. Rungs of the ladder are
made up of complementary bases joined by hydrogen bonds
OUTLINE THE ROLES OF SUTTON AND BOVERI IN IDENTIFYING THE IMPORTANCE OF CHROMOSOMES
Theodor Boveri experimented on sea urchins, and showed that a complete set of chromosomes is necessary for normal
development of an organism
 Demonstrated a connection between chromosomes and heredity
 Since a specific assortment of chromosomes was necessary for normal development, individual chromosomes
must possess different qualities
 Suggested that Mendelian traits may be connected to specific chromosomes
Walter Sutton studied chromosomes in testis of a grasshopper, and suggested that Mendel’s inheritance factors (genes)
are carried on chromosomes. He noted that:
 During meiosis, chromosomes in each grasshopper cell lined up in homologous pairs, and each pair was the
same size/shape
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Homologous pairs of chromosomes segregate during meiosis so that each gamete receives one chromosome
from each pair
 After fertilisation, the resulting zygote had a full set of homologous chromosomes
 Since hereditary factors are more numerous than chromosomes, each chromosome has to have many units
(genes)
 Chromosomes maintain a distinct structure even though they duplicate and divide
o Sutton suggested that “the association of paternal/maternal chromosomes in pairs and their
subsequent separation during meiosis may constitute the physical basis of Mendelian principles of
heredity
Sutton-Boveri theory is the chromosomal theory of inheritance, identifying that chromosomes carry many units of
inheritance (genes) and occur in distinct pairs
EXPLAIN THE RELATIONSHIP BETWEEN THE STRUCTURE AND BEHAVIOUR OF CHROMOSOMES DURING MEIOSIS AND
THE INHERITANCE OF GENES
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During meiosis, each chromosome makes a complete copy of itself. The duplicate chromosomes are attached to
the originals by centromere.
Homologous chromosome pairs line up in at the equator of the cell. Crossing over occurs, where sections of
chromosomes break off and rejoin onto the homologous chromosome.
o This means that ‘linked genes’ which are located on the same chromosome from the same parent, can
be separated by crossing over.
In the first division of meiosis, homologous chromosome pairs separate into two new cells, so that each of the
two new cells has half of the genetic information of the original, but a duplicate copy of each chromosome.
In the second division of meiosis, duplicated chromosomes separate to single strands, resulting in four sex cells
that are haploid
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Genes are located on chromosomes. Therefore, they are duplicated, then randomly assorted during
meiosis as homologous chromosomes are randomly assorted into haploid gametes
EXPLAIN THE ROLE OF GAMETE FORMATION AND SEXUAL REPRODUCTION IN VARIABILITY OF OFFSPRING
Gamete Formation:
 Haploid gametes formed in meiosis, contain half the normal (diploid) number of chromosomes because
homologous pairs separate
 Random segregation/independent assortment of homologous chromosomes during meiosis makes each
gamete different, causing variability of offspring
 Crossing over: during meiosis, chromosome material is exchanged between chromosomes
o Homologous chromosomes line up; adjacent chromatids split where they touch and join up with
different pieces
o Maternal and paternal chromosomes of each pair exchange segments of genes, making new
combinations of maternal/paternal alleles on chromosomes
o Ensures that linked genes on the same chromosomes aren’t always inherited together, and further
increases variability in offspring
Sexual Reproduction:
 In sexual reproduction, two gametes are brought together and, in fertilisation, fuse to form a diploid zygote
 Combining two gametes in fertilisation (each of which is randomly drawn from the huge group of gamete
possibilities from each parent due to random segregation and crossing over) drastically increases the possible
variations in offspring, as it is sheer chance that determines which gametes will be involved in fertilisation
 The chance of the same type of egg and same type of sperm again being produced and united is remote
PROCESS INFORMATION FROM SECONDARY SOURCES TO CONSTRUCT A MODEL THAT DEMONSTRATES MEIOSIS AND
THE PROCESSES OF CROSSING OVER, SEGREGATION OF CHROMOSOMES AND THE PRODUCTION OF HAPLOID
GAMETES
DESCRIBE THE INHERITANCE OF SEX-LINKED GENES, AND ALLELES THAT EXHIBIT CO DOMINANCE AND EXPLAIN WHY
THESE DO NOT PRODUCE SIMPLE MENDELIAN RATIOS
Sex linkage:
 Females have sex chromosomes XX; males have sex chromosomes XY
o All males receive their single X chromosome from their mother
 Characteristics determined by genes on the X chromosome are said to be sex-linked because they occur more
commonly in one sex than the other
o Males need only one allele for colour blindness on the X chromosome while females require two. This
results in many more males being colour blind than females because for females, the father would have
to be colour blind and the mother either colour blind or be a carrier.
A colour-blind person has a recessive allele (n) Since the Y chromosome carries no allele
for this trait, a single recessive allele on the X from their mother is effective in males. As a
result, simple Mendelian ratios are not produced.
o E.g. parents- XNY x XNXn
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Male offspring has 50% chance of getting recessive allele on the Y, and hence
expressing its phenotype
XN
Xn
XN
XN XN
XN X n
Y
XN Y
XnY
XN
XN
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Female offspring has 0% chance of expressing the recessive phenotype
In Mendel’s work, male and female children had equal probability of
expressing the phenotype
o E.g. parents- XnY x XNXn
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Male offspring has 50% chance of expressing the recessive phenotype
Female offspring has 50% chance of expressing the recessive phenotype
Xn
XN X n
XN X n
Y
XN Y
XN Y
E.g. parents- XnY x XNXN
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No offspring will express the recessive phenotype, but all females will be carriers
Co dominance:
 The heterozygote presents both phenotypes simultaneously, and may appear to have a phenotype intermediate
to those of the homozygous parents
o ‘Blending’ of phenotypes
o E.g. Snapdragons, Antirrhinum majus
 Parents- R1R1 (red) x R2R2 (white)
 F1- all R1R2 (all pink)  R1R2 x R1R2
 F2- 1 R1R1 (red) : 2 R1R2 (pink) : 1
R2R2 (white)
 Does not produce simple 3:1 F2 Mendelian ratio,
because heterozygous individuals have a third
phenotype, which is the simultaneous expression of
both alleles
o E.g. Southhorn cattle: Cross of a red-coated
and white-coated Shorthorn produces all
hybrid offspring with a ‘roan’ coat,
consisting of both red and white hairs


R
R
W
RW
RW
W
RW
RW
Co-dominant alleles show that the relationship between expression of alleles of a gene is not always one of
complete dominance
Apart from their phenotypic interaction, co-dominant alleles behave the same as alleles of genes that Mendel
identified.
EXPLAIN THE RELATIONSHIP BETWEEN HOMOZYGOUS AND HETEROZYGOUS GENOTYPES AND THE RESULTING
PHENOTYPES IN EXAMPLES OF CO-DOMINANCE
E.g. Shorthorn Cattle
 Homozygous RR individuals are red
 Homozygous WW individuals are white
 Heterozygous RW individuals are roan
Alleles present
AA or AO
Blood type
A
o
Heterozygous phenotype is an intermediate of the phenotypes of
homozygous R1 and homozygous R2 individuals
BB or BO
B
OO
O
E.g. Human blood
AB
AB
 A and B are both dominant to O
 Homozygous A individuals have blood group A
 Homozygous B individuals have blood group B
 Homozygous O individuals have blood group O
 Heterozygous AB individuals have blood group AB
o In the heterozygous AB phenotype, both the A and B phenotypes are simultaneously expressed
o When a homozygous A parent and homozygous B parent have a child, that child’s blood group will be
AB
DESCRIBE THE WORK OF MORGAN THAT LED TO THE UNDERSTANDING OF SEX LINKAGE

In the early 1900s, Thomas Hunt Morgan was trying to replicate Mendel’s work using the fruit fly Drosophila and
eye colour [W = red, w = white]
o Ideal species for breeding experiments because it:
 Has easily observable characteristics carried on 4
pairs of chromosomes
 Produces hundreds of offspring in a single mating
 Produces a new generation in 10-12 days
___________________________

Parents- XwY (white male) x XWXW (red female)

F1- XWY (red male) x XWXw (red female)
o

F2- XWY (red male), XwY (white male), XWXW (red female), XWXw (red female)
o

The expected ratio of 3 red: 1 white did appear, but all the white-eyed flies were males
Test cross- XwY (white male) x XWXw (red female from F1)
o
o
o

Since all F1 had red eyes, red eye colour was dominant and white was recessive
Used to determine if the red female from F1 was homozygous or heterozygous
Results were 50% of males were red, 50% were white; 50% of females were red, 50% were white
Showed that red females from F1 were heterozygous XWXw
 Hence, F2 should’ve exhibited the Mendelian 3:1 ratio, but it didn’t
Reciprocal cross- XWY (red male) x XwXw (white female)  1 white male : 1 red female
o
In this cross, the F1 generation did not consist of all red heterozygous individuals. This challenged
Mendel’s view that whether an allele came from the male or female pattern was irrelevant in
determining the offspring’s genotype.
__________________________
 Morgan hypothesised that gene for eye colour must be carried on X chromosome (was sex-linked) and that the
Y chromosome has no gene for eye colour.
o Therefore, all F1 females would be heterozygous, having inherited one recessive white allele from the
father, and one dominant red allele from their mother
o This idea was supported by results of the test cross
 In humans, X-linked genes include red-green colour blindness and haemophilia
o For a male to suffer from an X-linked condition, he only needs to inherit a single defective X-chromosome
from his mother
o


Females need two defective X-chromosomes with the recessive allele to express its phenotype. This is far
less likely to occur than in males
Conclusion: Some genes are located on the same chromosome that determines gender; the expression of these
is related to an offspring’s gender
*In genetics problems with sex linkage, use superscripts for alleles next to the X chromosome
SOLVE PROBLEMS INVOLVING CO-DOMINANCE AND SEX LINKAGE
X-linked dominant pattern
 Male with the trait passes it on to all his daughters and none of his sons
 Every affected person has at least one parent with the trait
 If a trait disappears from a branch of the pedigree, it does not reappear
 Affects more females than males
X-linked recessive pattern
 All sons of a female with the trait are affected
 All daughters of a male with the trait will be carriers
 All children of two individuals with the trait will show the trait
 More males than females will show the trait
OUTLINE WAYS IN WHICH THE ENVIRONMENT MAY AFFECT THE EXPRESSION OF A GENE IN AN INDIVIDUAL


Environment may not allow the particular characteristics of a gene to be fully revealed or expressed
E.g. two people with same genetic inheritance for tallness might grow to different heights because of
differences in nutrition or their health
 Studies on identical twins who are brought up in different environments show that these twins have larger
differences in certain characteristics than identical twins who are brought up in the same environment
 Genotype + Environment  Phenotype
Phenylketonuria
 Babies that inherit the homozygous recessive genotype pp from their parents cannot produce a certain enzyme
 If these babies are fed diets that include proteins that contain normal
quantities of the amino acid, phenylalanine (phe), the babies will suffer
brain damage.
 If the babies are fed with a special diet with very low levels of phe, they will
not suffer brain damage and will present a normal phenotype
o Therefore, phenotype of a child with genotype pp depends on
internal environment that is controlled by diet
Hydrangea plants
 This plants produce flowers, which have colouration dependent on acidity
or alkalinity (pH) of the soil in which they are grown
 In soil with acidic pH, pigments are a bright blue
 In soil with alkaline pH, pigments are a pale pink colour
American Alligator
 Sex is determined by the temperature they were incubated at during
embryonic development
o Eggs incubated at cooler temperatures turn into females, while warmer eggs turn into males
Sandaggers Wrasse
 Fish live in groups consisting of a single male with attendant females and juveniles
 In the presence of a male, all juvenile fish grow into females (due to certain chemicals released by the male)
 When the male dies, the dominant female undergoes physiological changes to become the male for the group
IDENTIFY DATA SOURCES AND PERFORM A FIRST-HAND INVESTIGATION TO DEMONSTRATE THE EFFECT OF
ENVIRONMENT ON PHENOTYPE
4.
The structure of DNA can be changed and such changes may be reflected in the
phenotype of the affected organism
PROCESS INFORMATION FROM SECONDARY SOURCES TO DESCRIBE AND ANALYSE THE RELATIVE IMPORTANCE OF
THE WORK OF:
– JAMES WATSON
– FRANCIS CRICK
– ROSALIND FRANKLIN
– MAURICE WILKINS
IN DETERMINING THE STRUCTURE OF DNA AND THE IMPACT OF THE QUALITY OF COLLABORATION AND
COMMUNICATION ON THEIR SCIENTIFIC RESEARCH




It was Wilkins’s idea to study DNA by X-ray crystallographic techniques.
Rosalind Franklin and Maurice Wilkins used X-ray crystallography to obtain an X-ray diffraction pattern of the
DNA molecule
o Rosalind Franklin assumed she’d be the only one working on DNA, but Wilkins assumed that she was to
assist in his work. Communication between the two was difficult, and probably slowed their progress
o Rosalind Franklin’s advances in X-ray diffraction techniques showed us the shape of DNA molecule; two
strands linked to form a tightly linked pair
 Franklin produced an extremely fine beam of x-rays, and arranged finer DNA fibres than ever
before in parallel bundles
o Rosalind Franklin suspected that all DNA was helical, but did not want to announce this finding until she
had gathered more evidence of this result. Wilkins showed her results to Watson and Crick without her
knowledge or consent
James Watson and Francis Crick had a close working relationship, and persisted even after the first failed model,
and being told to stop DNA research
o They published an accurate and successful double helix model of DNA, after examining:
 Franklin/Wilkins’ work
 Chargaff’s research finding that there are equal amounts of the four bases in DNA
 Linus Pauling’s discovery that some proteins have helical shapes
o In their model, two chains twisted into a double helix of alternating sugar/phosphate units linked by
pairs of four bases. Adenine always pairs with thymine; cytosine always pairs with guanine
Rosalind Franklin died of ovarian cancer. Watson, Crick and Wilkins received the Nobel Prize in
medicine/physiology for their determination of DNA’s structure
DESCRIBE THE PROCESS OF DNA REPLICATION AND EXPLAIN ITS SIGNIFICANCE
DNA Replication:
 DNA double helix is unwound by an enzyme
 DNA replication begins with separation of its two strands, so that the strands unzip to form a replication fork
o These parent strands will form the template for synthesis of complementary strand
o Binding proteins prevent strands from rejoining
 A complementary copy of each exposed strand is constructed by adding new nucleotide units (catalysed by
DNA polymerase)



The leading strand strand is built as a continuous strand
The lagging strand is
built by linking DNA
fragments (called
Okizaki fragments)
together
The two new doublestranded molecules
are called chromatids
Significance of DNA
Replication:
 Is that identical
copies of genes can
be made, and hence genetic information can be passed on to offspring.
 DNA replication is necessary for mitosis and meiosis to occur
o Mitosis (producing new cells with all the necessary genetic information) is needed for growth of an
organism, and repair
o Meiosis is needed for sexual reproduction. Self-replication is a necessary pre-requisite of life
OUTLINE, USING A SIMPLE MODEL, THE PROCESS BY WHICH DNA CONTROLS THE PRODUCTION OF POLYPEPTIDES




Each gene is a certain sequence of bases along a DNA strand, and is the information required to make a
particular polypeptide.
o Each triplet of bases, called a codon, codes for one
amino acid
o 61 different codons specify 20 different amino acids
Messenger RNA (mRNA): a ribonucleic acid which carries
information from DNA in nucleus to ribosomes in cytoplasm
Transfer RNA (tRNA): a ribonucleic acid consisting of a single
strand, which brings amino acids to the ribosome to be linked
together
o A different type of tRNA for each amino acid
 Each tRNA contains an anticodon which is
complementary to a codon on mRNA
Ribosomes: Made up of 2 subunits, and act as site for protein
synthesis in cytoplasm
o 3 binding sites to hold mRNA strand and 2 tRNA
molecules together temporarily
Transcription: process by which information on DNA is copied onto an RNA molecule
1) DNA strand in nucleus unwinds in area of required gene
2) RNA polymerase moves along the strand linking complementary RNA nucleotides
to form the pre-mRNA strand
o Start (AUG) and stop (UAA, UAG, UGA) codons (on RNA) control length of
mRNA strand
o Uracil (U) replaces thymine (T) as the complementary RNA nucleotide of
Adenine (A)
3) After the whole gene is copied, introns (non-coding regions) are spliced from the pre-mRNA and exons (coding
regions) are joined together to form mRNA
4) A poly-A tail, and a methylguanosine chemical cap, are added. The chemical cap assists in binding the mRNA to
ribosomes.
5) Modified mRNA moves from nucleus into cytoplasm
Activation of Amino Acids:
 In cytoplasm, an enzyme attaches amino acids to their respective tRNA molecules
Translation: process by which information on RNA molecule is used to make a new protein
1) mRNA and 2 tRNA molecules attach to ribosome
o mRNA strand binds on to ribosome at the end with start codon AUG
o Anticodon UAC on the tRNA carrying amino acid methionine binds to start codon AUG on mRNA within
the ribosome
o Second tRNA binds to the next mRNA codon
2) The 2 amino acids link by a peptide bond
3) Previous tRNA is released from ribosome, ribosome moves along mRNA
strand one codon at a time, another tRNA binds within the ribosome
and its amino acid links up to the previous. This step is repeated…
4) When a ‘stop’ codon is reached the polypeptide chain is released into
the cytoplasm
5) Further processing is necessary before final protein is formed, as
polypeptide chain is only primary structure
EXPLAIN THE RELATIONSHIP BETWEEN PROTEINS AND POLYPEPTIDES




Polypeptide: a single chain of amino acids
o Many proteins are made up of more than one polypeptide
Polypeptide chain forms primary structure
Folding/arrangement of polypeptide chain forms secondary/tertiary
structures
Joining of multiple polypeptides forms quaternary structure, and makes
a complete protein
PERFORM A FIRST-HAND INVESTIGATION OR PROCESS INFORMATION FROM
SECONDARY SOURCES TO DEVELOP A SIMPLE MODEL FOR POLYPEPTIDE SYNTHESIS
ANALYSE INFORMATION FROM SECONDARY SOURCES TO OUTLINE THE EVIDENCE THAT LED TO BEADLE AND
TATUM’S ‘ONE GENE – ONE PROTEIN’ HYPOTHESIS AND TO EXPLAIN WHY THIS WAS ALTERED TO THE ‘ONE GENE –
ONE POLYPEPTIDE’ HYPOTHESIS


George Beadle’s experiments on Drosophila fruit fly indicated that genes somehow affected eye colour in the fly
o He found that mutant eye colour was caused by a change in one protein
o Concluded that genes must influence heredity chemically (e.g. via proteins)
George Beadle and Edward Tatum used X-rays to produce mutated strains of a bread mould, Neurospora crassa
o Each strain lacked a different enzyme on the metabolic pathway to synthesise the essential amino acid
arginine, and hence could not grow normally
o By growing the different strains with different nutrient combinations, they were able to establish which
enzyme was lacking in each mutant strain
 Also found that each genetic mutation was at a specific locus on mould’s chromosome
o Concluded that different gene loci were associated with the production of each enzyme, leading to ‘one
gene, one enzyme’ hypothesis


Altered to ‘one gene, one protein’ hypothesis because some genes produced proteins which were not enzymes,
e.g. keratin, haemoglobin
Altered to ‘one gene, one polypeptide’
o The enzymes that Tatum and Beadle studied consisted of one polypeptide, but many proteins are made
up of more than one polypeptide
 Polypeptide: a single chain of amino acids
o Therefore, one gene is a portion of DNA specifying a single polypeptide chains. Several genes may be
required to specify a complete enzyme or other protein
PROCESS INFORMATION TO CONSTRUCT A FLOW CHART THAT SHOWS THAT CHANGES IN DNA SEQUENCES CAN RESULT IN
CHANGES IN CELL ACTIVITY
1) Changes in DNA sequence
2) Polypeptide chain is formed via transcription/translation with changes in amino acid sequences
3) Final protein has a changed primary structure
4) Arrangement of amino acids determines forces and bonding between polypeptide chains, so protein’s shape is altered
5) Protein’s function depends on its shape, so malformed protein may function incorrectly or not function at all
6) Proteins are vital to cell activity. Incorrectly functioning protein will result in changes in cell activity.
_________________
 If there is a simple substitution for a single base pair on a strand of DNA such as a G-C replaced by A-T, this will
result in a different amino acid codon forming a different polypeptide.
 If one base pair is lost from the sequence there will be a shift along the DNA molecule, producing vastly
different polypeptides. E.g. loss of thymine shown below

Cell activity is controlled by enzymes. Enzymes are formed from chains of polypeptides. If the chain of amino
acids forming the polypeptide is not in the right sequence, then the enzyme formed will not be functional, and
cell activity will be affected.
EXPLAIN HOW MUTATIONS IN DNA MAY LEAD TO THE GENERATION OF NEW ALLELES





Mutations: changes in DNA information on a chromosome
Any change in the base sequence in DNA results in changes to the polypeptides that are produced and is a
source of new alleles.
To produce changes in alleles, the mutation must occur in the sex cells of the organism which are then passed
on to the next generation.
Point mutation: change in a single nucleotide
Substitution: one base is replaced by another base



Deletion: one or more bases are lost from a chromosome
Insertion: an extra base inserted into the DNA
Frameshift: insertion or deletion of a base changes codon sequence along DNA strand, drastically changing the
polypeptide produced






Duplication: extra copy made of a sequence on same chromosome
Amplification: many extra copies of a sequence are found on a chromosome
Inversion: DNA sequence breaks and reattached the wrong way around
Translocation: a piece of DNA from one chromosome joins on to another chromosome
Position effect: when a changed DNA sequence affects genes near it
Aneuploidy: abnormal chromosome number
o A pair of chromosomes may fail to separate during meiosis (nondisjunction)
 On fertilisation, there will be either too many or too few chromosomes
o E.g. Down syndrome
Polyploidy: one or more extra sets of chromosomes
o All duplicate chromosomes may fail to separate during mitosis
 Resulting cell has double the normal chromosome number
o If it occurs in the zygote, whole new organism will be polyploid
o Polyploid fruits/flowers are usually larger than normal and plants grow more vigorously

Radiation:
 Ultraviolet radiation can cause deletion (bases in DNA strands to be lost)
o To repair this, enzymes in organism’s body may randomly incorporate bases into the gap, resulting in a
mutation
o Also may cause thymine bases in same DNA strand to link together, which means replication cannot
occur normally, causing cell death
 Other forms of radiation may break up DNA strands, or even break up whole chromosomes
o Results in mutation or cell death, depending on amount of damage to genetic material
Chemicals:
 Tautomeric shift: Chemicals may alter double bonds and position of hydrogen atoms in DNA, causing changes in
chemical shapes of bases
o Changed bases do not pair as usual during replication, resulting in production of a mutated DNA strand
 Some mutagens are carcinogens and may cause cancers
 Deamination: DNA base has amino group in its molecule replaced by a different group
o On replication, usual pairings do not occur, resulting in a mutated DNA strand
_________________________
 Induced mutation
o Plants are often deliberately exposed to mutagens, and scientists look for desirable changes in the
offspring, such as resistance to specific diseases
DISCUSS EVIDENCE FOR THE MUTAGENIC NATURE OF RADIATION
Mutagen: a natural or human-made agent which can alter the structure or sequence of DNA. Mutagens can be
carcinogens (cancer causing) or teratogens (birth defects causing)
 Most of the first generation of scientists who worked with radiation died of cancer, e.g. Marie Curie died of
leukaemia
 Hermann Muller received the Nobel Prize for showing that genes had the ability to mutate when exposed to Xrays
o Employed X-rays to produce point mutations in fruit fly Drosophila



o Discovered that rate of mutation increased linearly with amount of radiation received
Beadle and Tatum used X-rays to produce mutations in bread mould, to formulate their “one gene, one
polypeptide” hypothesis
Chernobyl nuclear accident has caused an estimated 32 000 deaths already
o Research indicates that incidence of cancer caused by radiation-induced mutation from Chernobyl is
expected to peak in 2005
o It is estimated that there is a 100 times increase in mutation rate among the descendents of victims of
the Chernobyl nuclear accident
Atomic bombs dropped on Hiroshima and Nagasaki released radiation. There was a tenfold increase in cancer
deaths directly after the bombs were dropped.
EXPLAIN HOW AN UNDERSTANDING OF THE SOURCE OF VARIATION IN ORGANISMS HAS PROVIDED SUPPORT FOR
DARWIN’S THEORY OF EVOLUTION BY NATURAL SELECTION

Sources of variation:
o Mutations in chromosomes and genes
o Random and independent segregation of chromosome pairs in meiosis
o ‘Crossing over’ of pieces of homologous chromosomes during meiosis
o Random fusion of gametes in sexual reproduction



This genetic variation is expressed in phenotype of an organism
Some phenotypes survive and reproduce better that others in a given environment
As a result of natural selection, individuals with particular genotypes become more common
o Increased understanding of sources of variation among individuals in a species, has supported Darwin’s
theory of evolution by showing us how the ‘variation in a population’ which is a fundamental postulate
for Darwin’s theory, has come about.
o Increased knowledge of genetics (how characteristics are passed on to offspring on chromosomes) has
also supported Darwin’s theory of evolution

Prolonged isolation and exposure to different selection pressures, may result in such different genotypes that
breeding between the two groups cannot occur successfully (2 species formed)
o Geographic isolation: e.g. a mountain range separates the two groups
o Behavioural isolation: organisms do not breed even if they occupy the same region, due to different
courtship patterns, mating calls, etc.
Genetic drift occurs when random changes occur in the types/frequencies
of genes in a small, isolated population, leading to evolution of new
species
Founder effect: genetic drift where a very small population becomes
geographically isolated from original population, leading to a loss of
genetic variation (see image)


DESCRIBE THE CONCEPT OF PUNCTUATED EQUILIBRIUM IN EVOLUTION AND HOW IT DIFFERS FROM THE GRADUAL
PROCESS PROPOSED BY DARWIN

Darwin’s theory of evolution: populations change gradually over time
o In fossil record, we should expect to see a long sequence including intermediate forms, recording
gradual change from ancestor to descendent
o But fossil record shows periods of genetic stability followed by episodes of mass extinctions and rapid
change


Eldridge and Gould’s theory of ‘punctuated equilibrium’ proposes that there have been periods of rapid
evolutionary change followed by long periods of stability/equilibrium
o If an environment remains stable, there would be little change in organisms. Natural selection only
occurs when conditions change.
How ‘punctuated equilibrium’ works
o When rapid change occurs in an environment, organisms either move out of the area or die
o Small isolated pockets of organisms may survive near or away from disturbed environment
o Small populations change at faster rate that large populations, resulting in ‘sudden’ appearance of new
species
PROCESS AND ANALYSE INFORMATION FROM SECONDARY SOURCES TO EXPLAIN A MODERN EXAMPLE OF ‘NATURAL’
SELECTION
Amongst large numbers of bacteria offspring, some individuals may carry genes that give them resistance to antibiotics.
These individuals are then able to survive and reproduce with reduced competition from other members of the same
species. Each generation will produce a higher percentage of individuals containing the resistant genes. The initial use of
an antibiotic results in good protection from bacteria. Over time the chemicals become less and less effective.
Chemicals, such as dieldrin and organophosphates, have been used extensively to control the sheep blowfly. However,
genetic resistance has occurred within the fly population that has made these chemicals ineffective. Continued use of
the insecticide has resulted in the mutation of a modifier gene that increases and maintains the resistance.
5.
Current reproductive technologies and genetic engineering have the potential
to alter the path of evolution
IDENTIFY HOW THE FOLLOWING CURRENT REPRODUCTIVE TECHNIQUES MAY ALTER THE GENETIC COMPOSITION OF
A POPULATION:
–
ARTIFICIAL INSEMINATION
–
ARTIFICIAL POLLINATION
–
CLONING



Artificial insemination: injection of male semen into a female
o Sperm is collected from a male with desirable characteristics, easily transported over large distances
and used to inseminate many females and produce many offspring
o Allows for the desirable characteristics from a male to be very efficiently brought into a population,
resulting in fast changes in the genetic composition of the population
Artificial pollination: dusting fertile stigmas with pollen from plants with desired characteristics
o Allows genetic changes to quickly become widespread within populations, as desirable characteristics
are spread through the population much faster than by natural breeding methods
Cloning: producing genetically identical organisms
o Provides genetic copies of animals with desired features more rapidly
than by traditional breeding techniques, and hence quickly alters the
genetic composition of the population favourably
o Whereas desirable characteristics may be lost in some offspring of
artificial insemination/pollination due to random segregation and
crossing over, cloning ensures that offspring produced have the
desired trait
o Over generations, genetic variability within the species is reduced
PROCESS INFORMATION FROM SECONDARY SOURCES TO DESCRIBE A METHODOLOGY USED IN CLONING

Plants may be cloned by tissue culture
1) Tissue is taken from the root tip
2) Cells are broken free in a blender
3) Cells are grown in a nutrient-rich medium, where they become unspecialised cells called calluses
 Composition of medium is altered depending on what type of plant
4) Treatment with appropriate plant hormones causes the calluses to develop into seedlings, and then into
mature, genetically identical plants

Animals (e.g. Dolly the sheep) may be cloned using nuclear transfer technology
1) Nucleus from a body cell of organism to be cloned is inserted into an egg cell with nucleus removed
 An electrical stimulus is used to fuse nucleus with an enucleated egg cell and to stimulate cell
division
2) At a certain stage in cell division, the embryo is implanted into a female ‘surrogate mother’
3) Embryo develops and ultimately forms a new organism which is genetically identical to the individual
that contributed the nucleus
OUTLINE THE PROCESSES USED TO PRODUCE TRANSGENIC SPECIES AND INCLUDE EXAMPLES OF THIS PROCESS AND
REASONS FOR ITS USE


Biotechnology: the use of various techniques to change living organisms at a molecular level
Transgenic organism: an organism which has some of its DNA from another species
o


A genetically modified organism (GMO) is not a transgenic species unless it is able to pass on its genetic
modification to the next generation (reproduce)
Transformation: when transfer of DNA occurs between species
Hybridisation: the production of an individual resulting from 2 genetically unlike parents
Steps in production of transgenic species:
1) A useful gene, and chromosome it’s on, are identified
2) The gene is isolated from its DNA strand using restriction enzymes
3) Recombinant DNA may be made by combining DNA from different species via annealing
4) Promoter DNA sequences for regulation may have to be added for the gene to work
5) Multiple copies of the gene may be made by Polymerase Chain Reaction (PCR)
6) Gene is inserted into the cell of another organism





Isolating genes using restriction enzymes
o Special restriction enzymes (restriction endonucleases) found in bacteria are used to ‘cut’ a useful gene
out of its DNA strand
o Each type of restriction enzyme cuts at a specific point in a sequence of nucleotides
 Cut ends are known as ‘sticky ends’
Making recombinant DNA by annealing
1) DNA strands from 2 different organisms are cut using same restriction enzyme, and then DNA pieces
from each are mixed together
2) Matching sticky ends will be attracted to each other and connect up
3) DNA ligases are added to annealed DNA fragments to seal and strengthen the bonds of new
recombinant molecules
Addition of promoter sequences
o An isolated gene cannot function; it needs a promoter sequence
attached to ensure that the gene will work
o Promoter sequences on DNA strand regulate when the gene is
active, how much protein is made, and in which cells the gene
will function
Polymerase Chain Reactions (PCR) to make copies of genes
 For large scale genetic engineering, many copies of
useful genes must be made
1) DNA molecule containing required gene, DNA polymerase, and a
large quantity of the 4 nucleotide bases and
‘primers’ are mixed together
2) Mixture is heated at 98⁰C for 5 minutes to separate
the 2 DNA strands
3) Mixture is cooled to 60⁰C. Primers anneal to ends of
separate DNA strands. DNA polymerase catalyses
synthesis of complementary DNA strands, resulting
in double the original number of DNA molecules
4) Repeated cycles of heating and cooling (every 2
mins) produces large quantities of required DNA
Inserting genes into bacteria using plasmids
 Plasmids (small circular pieces of DNA in
bacteria) can be used as vectors to transfer
genes into bacteria
1) Same restriction enzyme splits human chromosome
with required gene and the bacterial plasmid with a
gene for antibiotic resistance. The required human gene joins with plasmid via annealing and DNA
ligases. Many copies of the gene are made with PCR.
2) Treating bacteria with cold calcium chloride and heat softens bacterial wall, allowing plasmid to
penetrate some of the bacteria. Bacteriophages (viruses that infect bacteria) can also be used as vectors
to insert genes into bacteria.
3) The bacteria are cloned rapidly in a medium with antibiotic. Since the bacteria which took up copies of
the plasmid have antibiotic resistance from the same plasmid, only these bacteria will survive. In effect,
the antibiotics select only the transgenic bacteria.
4) Bacteria are cultured, and hormones produced by modified bacteria are harvested and used to treat
people
o Human genes that code for production of insulin and human growth hormone have been inserted into
bacteria
 Insulin treats people with insulin-dependent diabetes
 Human growth hormone treats children with specific growth defects
 Ti (tumour inducing) plasmid insertion: Inserting genes into plant cells using a soil bacterium
o Agrobacterium tumefaciens naturally causes disease by inserting a plasmid into a plant cell
1) Recombinant plasmid introduced into Agrobacterium
2) Co-culture of transformed Agrobacterium with isolated plant cells, yields transformed plant cell
3) Plant cells grow into a callus in nutrient medium, and callus yields healthy plantlets with new
traits
 Microinjection: Genes can be transferred into animal cells using very fine glass micropipettes
 Particle guns can be used to shoot DNA-coated microscopic gold/tungsten pellets directly into cells
 Electroporation uses electric pulses to create small pores in the nuclear membrane through which DNA is
inserted
An example of a transgenic species is genetically engineered salmon which have the gene coding for the protein bGH
(bovine growth hormone)
DISCUSS THE POTENTIAL IMPACT OF THE USE OF REPRODUCTION TECHNOLOGIES ON THE GENETIC DIVERSITY OF
SPECIES USING A NAMED PLANT AND ANIMAL EXAMPLE THAT HAVE BEEN GENETICALLY ALTERED
Plant:
 Bacillus thuringiensis (Bt) is a bacterium that produces toxins that kill insects
o Toxins are specific to a few species of insects, and are broken down in sunlight
o Pesticide sprays containing dead Bt bacteria are used successfully on crops
 Genetic engineering: inserting Bt genes that make Bt toxin directly into plants
o These tomatoes, corn, potatoes and cotton produce toxin continuously, so are more resistant to insect
attack
 There are concerns that the target insects will become resistant to Bt chemicals
 If more farmers plant genetically modified crops, then local varieties will die out at an increasing rate
 If Bt cotton become standard cotton crop, then other varieties will be lost, and species itself may become
vulnerable if environmental conditions change
o Large genetic variety is essential for species to survive significant environmental changes
Animals:
 The gene coding for the protein, BGH (bovine growth hormone), has been incorporated into the genes of
salmon.
 Outcome – larger, faster growing fish
 The fish are kept in ponds that offer no escape to the wild because of concern that they will reduce biodiversity
in natural ecosystems
Genetic Diversity:
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Biodiversity is needed to provide clean water, air, productive soil, and recycle matter
Biodiversity is essential to enable new chemical structures to be discovered which will benefit humans (food)
o E.g. Acacia seeds from Australia may enhance diets in Africa
Biological diversity offers great opportunities for discovering living resources essential to human survival
(medicine)
o E.g. Prostaglandin E2, a substance which could treat gastric ulcers, was discovered in gastric-brooding
frogs (thought to be extinct)
*Moving genes from species to species may increase genetic diversity
*Cloning can be used to preserve the numbers of endangered species and thus maintain genetic diversity
However, cloning also reduces genetic diversity as offspring are identical to each other and their parent
organism
ANALYSE INFORMATION FROM SECONDARY SOURCES TO IDENTIFY EXAMPLES OF THE USE OF TRANSGENIC SPECIES
AND…
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Bt cotton which produces a chemical that kills some insects
Blue gene extracted from petunia is introduced into carnation plant cell by recombinant plasmid, to make a blue
carnation: ‘Moondust’
Herbicide tolerant soy bean, corn, potato
o Also higher yielding and lower costing
Transgenic sheep that can secrete the protein alpha-1, used to treat human lung disease
Salmon with bovine growth hormone gene
Potato plants:
 A pea gene for lectin has been incorporated into potato plants.
 Outcome – protects against insect attack. Lectin is a protein which interferes with digestion in insects.
 Evaluation – Protection against insect attack improves the success of growing potatoes. Concerns exist about
controlling the ‘escape’ of these transgenic potatoes into the wild, as they may outcompete other varieties and
reduce genetic diversity
USE AVAILABLE EVIDENCE TO DEBATE THE ETHICAL ISSUES ARISING FROM THE DEVELOPMENT AND USE OF
TRANSGENIC SPECIES
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Effects on transgenic species
o E.g. cows treated with genetically engineered bGH (bovine growth hormone) increase milk production
 Risk of mastitis, infection to the nipple
Moral questions about creating transgenic species
o Lab mice bred to automatically develop diseases for scientific study
o Should we be tampering with nature in this way?
o Is it right to change living organisms for commercial gain?
Concern over return of the eugenics movement
o Selective breeding of desirable traits, similar to actions of Nazi Germans
Genetically engineered organisms may create strains of resistant diseases
Genetically modified foods may cause harm when eaten