Download Blueprint of Life

Blueprint of Life – Syllabus
1. Evidence of evolution suggests that the mechanisms of inheritance,
accompanied by selection, allow change over many generations.
DP1 “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
Changes in physical conditions in the environment
 These include natural conditions, such as temperature and the availability of
water.
 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. Food
was nutritious and abundant; there was no need for specialised grinding
teeth.
 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.
Changes in chemical conditions in the environment
 Chemicals that can affect the evolution of species include salts and elements,
such as iron. For example, many parts of Australia have soils that have a high
salinity. There are a range of salt tolerant plants that have evolved to inhabit
those areas. The animals that feed from these plants have also evolved to
inhabit those areas.
 The sheep blowfly, Lucilia cuprina, is a major problem to the Australian sheep
industry. It stresses, weakens and can be lethal to sheep when larvae, laid by
females, burrows into wounds and wet wool. Chemicals, such as dieldrin and
organophosphates, have been used extensively to control the blowfly.
However, genetic resistance has occurred within the fly population that has
made these chemicals ineffective. Withholding a particular insecticide for a
time allowed the resistance of this particular blowfly population to drop.
Continued use of the insecticide has resulted in the mutation of a modifier
gene that increases and maintains the resistance. Thus, the insecticides can
never be effective again, regardless of the number of blowfly generations
that pass.
Competition for resources
 This occurs within a species and between species. If a new species is
introduced into an area then the competition may lead to different species
using different resources.
 Resources can include food, space or mates. If populations that live in the
same area could specialise on slightly different resources or breed at
different times, they would avoid direct competition.
 Some species of fruit fly have evolved into different species with each
confined to a different type of fruit tree. This is possible if there are different
flowering and fruiting times on each tree type suited for different breeding
cycles in the fruit flies. Eventually, two distinct species can result.
DP2 “describe, using specific examples, how the theory of evolution is supported
by the following areas of study:”
Palaeontology
 The fossil record provides a time line of evolution of life engraved in the
order in which the fossils appear in rock layers. Some parts of the fossil
record show a gradual change in life forms over millions of years.
 Of particular interest are transitional fossils that have characteristics
belonging to ancestral and descendant groups. The most famous transitional
form is Archaeopteryx. This is a fossil first thought to be a therapsid reptile.
Its reptilian features include teeth and a reptilian-like skeleton. However,
Archaeopteryx also had feathers and a wishbone sternum used to attach
flight muscles. This provides evidence of an evolutionary pathway from
dinosaurs to birds.
Biogeography
 Charles Darwin and Alfred Russell Wallace both observed the distribution of
species into different biogeographic regions and saw this as major evidence
to support the theory of evolution. They argued that animals in different
regions had come from ancestors in that region and had adapted over time to
the conditions there. Special Creation, the prevailing religious-based
explanation of the time, did not explain why islands with similar conditions
did not contain the same flora and fauna. Darwin proposed that migration
and evolution were much more satisfactory explanations for the unique flora
found in places such as Australia.
Comparative embryology
 There is an obvious similarity between embryos of fish, amphibians, reptiles,
birds and mammals. A comparison of embryos of vertebrates shows that all
have gill slits, even though they do not remain later in life, except in fish. This
indicates a fundamental step that is common to all vertebrates and supports
the idea of a common ancestor.
Comparative anatomy
 Anatomical structures on different organisms that have the same basic plan
but perform different functions are called homologous structures.
Homologous structures are evidence for evolution. The structures are shared
by related species because they have been inherited in some way from a
common ancestor.
 An example of an homologous structure is the pentadactyl limb found in
amphibians, reptiles, birds and mammals. The basic plan consists of one bone
in the upper limb, two in the lower limb leading to five fingers or toes. 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.
Biochemistry
 Recent advances in technology have allowed comparison of organisms on a
molecular basis rather than simply comparing structures. This was previously
impossible between such distantly related organisms as an orchid and a
mouse.
 The study of amino acid sequences shows that more closely related species
share more common sequences than do unrelated species. Particular
evidence has been derived from the amino acid sequence in haemoglobin,
showing that humans and rhesus monkeys share all but eight amino acid
sequences whereas there are 125 amino acid differences between humans
and lampreys. This supports the fossil, embryological and anatomical
evidence that humans are more closely related to rhesus monkeys than they
are to lampreys.
DP3 “explain how Darwin/Wallace's theory of evolution by natural selection and
isolation accounts for divergent evolution and convergent evolution”


Divergent evolution occurs when closely related species experience quite
different environments and as a result vastly different characteristics will be
selected. The species, over time, will evolve differently and will eventually
appear quite different. For example, elephants are large plains-dwelling
animals that are closely related to a small guinea pig-like animal called a
hyrax. Hyraxes live amongst rocky outcrops on mountains. Comparison of
skeletons indicates the close relationship between the two groups.
Convergent evolution occurs when two relatively unrelated species develop
similar structures, physiology or behaviours in response to similar selective
pressures from similar environments. For example, dolphins (mammals) and
sharks (cartilaginous fish) have evolved a streamlined body shape and fins
that enable them to move efficiently through their aquatic environment, yet
they are only remotely related as vertebrates. Communal social behaviour
has developed independently in ants, termites and bees.
SC DP1 “plan, choose equipment or resources and perform a first-hand
investigation to model natural selection”
Stick bird
Toothpicks are mixed and scattered randomly over a measured grassed area. Stick
birds (students) are later brought to that area and remain outside a 'fence'. They are
told to prey on the 'worms' in the field (collect as many toothpicks as they can) in a
given time. After 3 minutes, the 'stick-birds' are driven from the field by the 'farmer'
(teacher). They escape back to the classroom.
Tally and compare the numbers of green and cream toothpicks recovered. Calculate
percentages recovered of each colour.
SC DP2 “analyse information from secondary sources to prepare a case study to
show how an environmental change can lead to changes in a species”
Starting information: Possible case studies of changes in a species
Changes in physical conditions in the environment
The teeth of kangaroos have evolved in response to changes in physical conditions in
Australia over the last 25 million years.
Changes in chemical conditions
Chemicals, such as dieldrin and organophosphates, have been used extensively to
control the sheep blowfly, Lucilia cuprina. Genetic resistance has occurred within the
fly population in response to these chemicals.
Competition for resources
Some species of fruit fly have evolved into different species with each confined to a
different type of fruit tree.
SC DP3 “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”
Perform a first-hand investigation by observing a range of vertebrate forelimbs to
compare their structures. Use at least three different types of vertebrates.
SC DP4 “use available evidence to analyse, using a named example, how advances
in technology have changed scientific thinking about evolutionary relationships”
Until the 1950s, the relationships between organisms were worked out by
similarities in anatomical features. At this time, it became possible to analyse protein
sequence data and DNA sequence data. Proteins, such as haemoglobin, could now
be compared and similarities worked out based on biochemical similarity. If the rate
of change is approximated, it is possible to work out a molecular clock that estimates
the time since two organisms shared a common ancestor.
SC DP5 “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”
By the beginning of the 19th century, a great deal of evidence was available to the
scientific community that supported evolution. What was missing was a plausible
mechanism to explain how evolution was occurring. Charles Darwin and Alfred
Wallace independently arrived at evolution as a result of natural selection. Darwin
gathered evidence after sailing on the HMS Beagle to South America and the
Galapagos Islands. By the early 1840s, he had documented the main points of his
theory.
Wallace was a British naturalist working in Indonesia in the mid-1850s. In 1858,
Wallace sent a copy of his work to Darwin. Darwin's colleagues encouraged him to
publish The Origin of Species at the same time and so receive the credit for his years
of work and insight. The Origin of Species included overwhelming evidence to
support Darwin's conclusions. Even though the Darwin/Wallace theory of natural
selection caused a furore amongst Victorian society in England when published,
scientific thinking was gaining respectability and becoming an important mechanism
for change.
The theory of evolution has encountered opposition since it was first introduced.
This is because it can be seen as a threat to religious and social beliefs.
2. Gregor Mendel’s experiments helped advance our knowledge of the
inheritance of characteristics.
DP1 “outline the experiments carried out by Gregor Mendel”
Genetics is the study of heredity. Heredity is the transfer of characteristics from one
generation to the next. Its origins can be attributed to Gregor Mendel. Mendel was
an Austrian monk born 1822. He studied the inheritance of characteristics in pea
plants.
He bred two groups of pea plants, over many generations until the offspring showed
no variation from the parents.
DP2 “describe the aspects of the experimental techniques used by Mendel that led
to his success”
He bred two groups of pea plants, over many generations until the offspring showed
no variation from the parents. This ensured he had pure-breeding plants. This group
became known as the P generation.
He crossed these two groups by manually transferring pollen grains from one flower
to another. He prevented self-pollination by removing the stamens of one pea plant.
The offspring became known as the F1 generation(first filial generation). Mendel
then allowed the F1 generation to interbreed to obtain the F2 generation.
Why was he Successful?
Mendel designed his experiments in such away to ensure successful accurate results.
1. He studied a large number of characteristics in the plants.(Form of
repetition/reliability)
2. He carried out a large number of crossed.
3. He used pure-breeding lines. (Form of accuracy)
4. He made exact counts of characteristics. (Form of accuracy)
He studied separate identifiable characteristics that occurred in pairs.
DP4 “distinguish between homozygous and heterozygous genotypes in
monohybrid crosses”
When both alleles are the same e.g. BB (both dominant) this is called homozygous
When the alleles are different not carrying the same information e.g. Bb this is called
heterozygous.
BB = homozygous dominant
Bb = heterozygous
bb = homozygous recessive
DP5 “distinguish between the terms allele and gene, using examples”
Hair colour is gene, brown is the allele.
DP6 “explain the relationship between dominant and recessive alleles and
phenotype using examples”
Dominant allele means it will show through in the persons physical appearance
Recessive allele will turn up only if no dominant allele is present.
Dominant alleles are always shown as a capital letter e.g. B = black
Recessive alleles are always shown as a lower case letter e.g. b = blonde
Genotype – This is a persons genetic makeup (use letters big B, little b)
Phenotype – This is your physical appearance (physical description 50% of babies will
have brown hair) If dominant will show through, if not dominant it will not show
through unless there is 2 recessive alleles.
DP7 “outline the reasons why the importance of Mendel’s work was not
recognized until some time after it was published”
Mendel Ignored:
- lack of formal education/scientific training
- lack of public understanding
- isolated
- timing coincided with Darwin (was overshadowed by evolution)
- publication (published in a very small scientific journal with very small
audience)
SC DP1 “perform an investigation to construct pedigrees or family trees, trace the
inheritance of selected characteristics and discuss their current use”
A pedigree is a family tree showing a line of descent. It can be used to trace the
occurrence of inherited traits in parents and offspring through a number of
generations.
By convention, circles represent females and squares, males. A line between a
square and a circle represents a union and a line down indicates offspring from the
union.Filled in symbols represent individuals displaying the phenotype being studied.
For example:
Pedigrees are valuable tools in genetic counselling. It allows a pattern of inheritance
to be traced throughout generations of a family. This can allow identification of the
genetic disease and advice can be made available on the probability of a couple
having an affected child. Cystic fibrosis is an example of a recessive genetic disease.
Huntington's chorea is an example of a dominant genetic disease.
SC DP2 “solve problems involving monohybrid crosses using Punnett squares or
other appropriate techniques”
A monohybrid cross involves the inheritance of one characteristic. All problems apply
Mendel's basic laws of inheritance. The following is typical of a problem that uses
Punnett squares to solve problems involving monohybrid crosses.
SC DP3 “process information from secondary sources to describe an example of
hybridisation within a species and explain the purpose of this hybridization”
Hybridisation means the breeding of two different types of plants or animals. For
example, a mule is the result of the union between a horse and a donkey, two
different species. The resulting animal has desirable characteristics from both
parents but all mules are sterile and cannot produce any offspring. Hybridisation also
occurs between different varieties or breeds within a species, such as dog, cattle or
sheep breeds. Many, probably most agricultural animals and plants are the result of
hybridisation. This results in offspring with desirable characteristics e.g. cross
breeding cattle to produce better meat or to be tick resistant and Triticale a grain
that is a cross between wheat and rye, two different species. Hybridisation is a good
way of producing new commercial plants and animals.
3. Chromosomal structure provides the key to inheritance.
DP1 “outline the roles of Sutton and Boveri in identifying the importance of
chromosomes”
Boveri and Sea Urchins
Betwenn 1896 and 1904, he carried out experiments on sea urchin eggs, studying
the behavior of the cell nucleus and chromosomes during meiosis and after
fertilization. Sea urchin eggs were ideally suited for study because they could be
easily fertilized in a laboratory and have a quick (48 hour) time frame for larval
development.
Boveri's findings
It was already known at the time that each species of living organism has a set
number of chromosomes and that, during fertilisation, an egg cell and a sperm cell
fuse. Boveri's experimental work with sea urchins showed that the nucleus of the
egg and sperm each contribute the same amount (50%) of chromosomes to the
zygote (fertilised egg), making a connection between chromosomes and heredity.
His experiments showed:

when a normal egg and sperm fused, the resulting offspring showed
characteristics of both parents

if the nucleus of only one parent was present, the larvae resembled that parent,
but showed abnormalities. When an egg, whose nucleus had 'been removed,
was fertilised with a sperm, the resulting sea urchin larvae showed
characteristics similar to the male parent. However, they were smaller, had only
half the normal number of chromosomes and showed some abnormalities.
From this he deduced that:
—a complete set of chromosomes (that is, chromosomes in pairs) is needed for
normal development
—the inheritance 'factors' are found on chromosomes within the nucleus—that is,
chromosomes are the carriers of heredity.
Sutton and grasshoppers
Walter Sutton (1877-1916), an American cytologist, studied meiosis in cells of
grasshoppers (Brachystola magna). In contrast to the eminent Boveri, Sutton
was a young, unknown graduate student who produced remarkable and detailed
drawings of his findings in cytology. As a result of his observations, he made the
connection between the behaviour of chromosomes during meiosis and Mendel's
laws of heredity. His independent findings (1902-4), together with those of
Boveri (1902), formed the basis of the chromosome theory of inheritance.
Suttons Findings
Sutton's observations of meiosis in grasshoppers revealed that:
 chromosomes occur in distinct pairs, visible during meiosis in grasshopper cells;
one chromosome of each pair is paternal and the other maternal (today
termed homologous pairs) and the chromosomes in each pair have the same
size and shape
 during meiosis (reduction division), the chromosome number of a cell is halved:
the chromosomes in each pair of chromosomes separate (just like Mendel's
factors segregate—his law of dominance and segregation) and each gamete
receives one chromosome from each pair
 fertilisation restores the full number of chromosomes in the zygote.
He concluded that chromosomes were the carriers of heredity units and
behaved in the same manner as Mendel's 'factors of inheritance' (genes).
In addition, Sutton stated that:
 Chromosomes arrange themselves independently along the middle of the cell
just before it divides—that is, they assort independently of each other
during segregation, like Mendel's factors (evidence for Mendel's law of
independent assortment)
 Chromosomes are units involved in inheritance. Sutton, like Boveri, also
believed that several Mendelian`factors' must be present in one chromosome
and could therefore be inherited as a unit. (This'is what we term 'linkage'
today. It will be dealt with in more detail on page 173—sex-linkage).
DP2 “describe the chemical nature of chromosomes and genes”
Chromosomes are compact tread-like molecules made up of 40% DNA and 60%
histone protein. Chemically each gene is made up of a portion or section of DNA that
codes for particular information. DNA consists of sugar phosphate and nitrogen
bases arranged in nucleotides.
DP3 “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.”
DP4 “explain the relationship between the structure and behaviour of
chromosomes during meiosis and the inheritance of genes”

Chromosomes are made of DNA. Genes are coded within the DNA on the
chromosomes. During division each chromosome (which therefore includes the
genes) makes a complete copy of itself. The new chromosome is attached to the
original chromosome by a centromere. In the initial division of meiosis the
homologous chromosomes line up in matching pairs and one of each pair of
homologous chromosomes moves into a new cell. Next the duplicated
chromosomes separate to single strands resulting in four sex cells that are
haploid, (ie contain half the chromosome number of the original cell).

The genes are located on the chromosomes. They are duplicated during the first
stage of meiosis and are then randomly assorted depending on which
chromosomes from each pair enters which new haploid cell during the first and
second division.
DP5 “explain the role of gamete formation and sexual reproduction in variability of
offspring”



Gamete formation results in the halving of the chromosome number (n)
(diploid to haploid) and sexual reproduction results in combining gametes
(haploid to diploid) to produce a new diploid organism (2n). The processes
involved in forming this new organism result in variability of the offspring.
Gametes are formed during the process of meiosis. In meiosis there are two
stages that lead to variability. These are:
o random segregation of individual chromosomes with treir associated
genes ie, different new combinations of the original maternal and
paternal chromosomes and
o the process of crossing over where the maternal and paternal
chromosomes of each pairmay exchange segments of genes making
new combinations of genes on the chromosomes.
In sexual reproduction each female or male cell produces 4 sex cells
(gametes) from the process of meiosis. Each of these sex cells is haploid (has
half the normal chromosome number) and has a random assortment of
genes from the parent. The genes (Mendel's alleles) are separated and the
sex cells have a random assortment of dominant and recessive genes. More
variability is introduced depending on which sex cells are successful in
fertilisation. The resulting embryo has a completely different set of genes
from either of the parents.
DP6 “describe the inheritance of sex-linked genes, and genes that exhibit codominance and explain why these do not produce simple Mendelian ratios”
Mendel was fortunate in his choice of factors as they all showed dominant/recessive
characteristics. However, sex-linked genes and genes that are co-dominant do not
display the phenotype ratioos predicted by Mendel's laws.
An example of sex-linked inheritance is red-green colour blindness in humans. The
gene is carried on the X chromosome and there is no corresponding gene on the Y
chromosome. Therefore 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 the father would have to be colour blind and the
mother either colour blind or be a carrier for colour blindness. As you would expect
the sex of offspring to be 50% male and 50% female the occurrence of colour
blindness is higher in males than would be expected from a simple pair of dominant
and recessive genes. Take the cross between a normal female XN XN and a colourblind male X n Y.
All offspring have normal sight. But if the female is a carrier for colour blindness and
crosses with a normal male then 50 % of the males will be colour blind and none of
the females.
Human blood types are another example of co-dominance. Human blood types give
different results from Mendelian ratios. When a homozygous male with AA alleles
crosses with a homozygous female with BB alleles then all of the offspring will be a
different phenotype from the parents (group AB).
DP7 “describe the work of Morgan that led to the understanding of sex linkage”
Thomas Hunt Morgan studied the fruit fly, Drosophila melanogaster, in genetic
experiments. After a year of breeding flies, looking for new characteristics, Morgan
found a male fly with white eyes in his breeding stock. The normal or ‘wild’ eye
colour is red. The white-eyed individual was probably a mutant.
He mated this white-eyed male with a red-eyed female and all F1 had red eyes,
showing that red eyes are dominant over white.
When Morgan crossed two of the F1 generation the offspring had a phenotypic ratio
of 3 red-eyed offspring : 1 white-eyed offspring. However, the white-eyed trait was
only present in the males, with half the males having white eyes and half having red
eyes
DP8 “explain the relationship between homozygous and heterozygous genotypes
and the resulting phenotypes in examples of co-dominance”
In genetic traits that show co-dominant inheritance, heterozygous individuals show
both the dominant and recessive trait in their phenotype.
Examples:
– AB blood group in humans
– Roan cattle (referred to as red alleles if it crossed with a white cattle you get
patched red and white cows, both show through in phenotype)
– Andalusian chickens (black feathers crossed with white feathers appears to
be blue, both show through in phenotype)
Give the genotypic ratio of a cross between two roan cattle
Gametes
R
W
1 RR : 1 WW : 2 RW
R
RR
RW
W
RW
WW
Give the phenotypic ratio of the cross between a roan cow and a white bull.
Gametes
W
W
1 Roan : 3 White
R
RW
WW
W
WW
WW
Give the phenotypes and genotypes of the offspring between 1 pink snapdragon and
1 red snapdragon.
Gametes
R
R
RR
R
RR
Phenotypes are 50% red and 50% pink
Genotypes are 50% RR and 50% RW
W
RW
RW
DP9 “outline ways in which the environment may affect the expression of a gene in
an individual”
- The appearance of an individual is not based solely on their genetic information.
The environment of the organism also plays a part.
- Hydrangeas are plants that have different flower colour (pink or blue) depending
on the pH of the soil they are grown in. In acid soils (less than pH 5) Hydrangeas
are blue. In soils that have a pH greater than 7 Hydrangeas are pink. The pH has
an effect on the availability of other ions in the soil and it is these ions that are
responsible for the colour change.
Sex Linkage Patterns
X-Linked recessive:
 All the sons of an affected female will be affected
 All the daughters of an affected male will be carriers
 All children of two affected parents will have the trait
 In a large sample, more males than females will show the trait
X-Linked dominant:
 A male with the trait passed it onto all of his daughters and none of his sons
 A female with the trait may pass it onto her daughters and sons
 Every affected person has at least one person with the trait
 In a large sample size, there are more affected females than males
SC DP1 “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”
Use plasticine or pipe cleaners to model the process of meiosis to demonstrate
crossing over, segregation of chromosomes and the production of haploid gametes.
Or use prepared slides showing meiosis.
SC DP2 “solve problems involving co-dominance and sex linkage”
1. A man with haemophilia marries a woman with no family history. What % chance
do they have of having a haemophiliac child?
Alleles
X
X
h
h
X
XX
XXh
Y
XY
XY
2. A woman who carries the gene for haemophilia marries a man without
haemophilia. What % chance of a haemophiliac child?
Alleles
X
Xh
X
XX
XXh
Y
XY
XhY
 25% chance of a haemophiliac child.
3. A haemophiliac male marries a carrier female. What % chance of a haemophiliac
child?
Alleles
X
Xh
Xh
XXh
Xh Xh
Y
XY
XhY
 50% chance of a haemophiliac child
4. A woman with haemophilia marries a normal man. What % chance of a
haemophiliac child?
Alleles
Xh
Xh
h
X
XX
XXh
Y
XhY
XhY
 50% chance of haemophiliac child. If a woman has haemophilia all of her sons
will have it, if a man has haemophilia he has inherited it from Mum.
SC DP3 “identify data sources and perform a first-hand investigation to
demonstrate the effect of the environment on phenotype”
Studies on identical twins separated at birth are useful to determine how much the
phenotype is determined by the environment. Identical twins have the same
genotype, so any differences in phenotype could be determined by the environment.
Other studies that are useful are long-term studies on height of individuals. For
example, Japanese people who grew up in America on average were taller than
Japanese people who grew up in Japan. Better nutrition was responsible for the
Japanese people to reach their genetic potential. This has been shown in an increase
in the height of the average Japanese person over the last fifty years as nutrition has
improved.
4. The structure of DNA can be changed and such changes may be reflected in the
phenotype of the affected organism.
DP1 “describe the process of DNA replication and explain its significance”
Steps:
1. Double helix unwinds
2. The two strands begin to separate
3. Free nucleotides attach to the exposed bases (maintaining base pairing rule
A-T, T-A, G-C, C-G)
4. Weak hydrogen bonds bands reform between the bases and the strands
begin to ‘re-zip’
5. Each DNA molecule re-twists back into the double helix
Significance:
Mitosis:
It is significant because you do not want any change, you want the new cell to do it’s
intended job, whether it be a skin cell, nerve cell etc.
Meiosis:
Ability to exactly copy information to be passed onto offspring, to make sure they
receive the correct phenotypic characteristics.
DP2 “outline, using a simple model, the process by which DNA controls the
production of polypeptides”
DNA stores genetic information. The sequence of bases determines the sequence of
amino acids in protein molecules. The smallest unit that can code for an amino acid
is a codon, or triplet of bases. For example, the DNA code CCA codes for an amino
acid called glycine. Protein synthesis involves the transcription of the code from DNA
to mRNA and then the translation of the code from mRNA to tRNA.
The first step in polypeptide synthesis involves the unwinding of the DNA, and the
copying of one strand by mRNA. Once the mRNA has the code for the protein, it
moves from the nucleus into the cytoplasm.
In the cytoplasm the mRNA moves to a ribosome where it binds to the ribosome at
the end with a ‘start’ codon. In translation, a tRNA in the cytoplasm moves to the
codon on the ribosome. At one end of the tRNA there is an anticodon that matches
the codon of the mRNA, and at the other end of the tRNA is an amino acid. Once the
first amino acid is attached, the second tRNA brings in its amino acid to attach to the
next codon and this slowly builds up the sequence of amino acids.
Note: mRNA does not have a T it has a U
DNA
A
T
G
C
C
T
G
A
C
A
T
G
mRNA U
A
C
G
G
A
C
U
G
U
A
C
tRNA
A
U
G
C
C
U
G
A
C
A
U
G
Codon = block of 3
Anticodon = Codon but once it is tRNA
DP3 “explain the relationship between proteins and polypeptides”
A protein is made up of one or more polypeptides. A polypeptide is made up of a
chain of many amino acids.
DP4 “explain how mutations in DNA may lead to the generation of new alleles”
 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.
DP5 “discuss evidence for the mutagenic nature of radiation”
Evidence for radiation as a mutagen:
 Marie Curie
- Worked with radioactive substances
- Died of cancer
 Chernobyl –
- Leaking of radioactive waste
- Cancer, birth defects
 Rosalyn Franklin
- Worked with X-Rays
- Died of cancer
 Hiroshima
- Radiation from bombs
- Cancers, birth defects
 Beadle and Tatum
- X-rays bread mould
- Mould mutated and was unable to produce a specific enzyme
 Skin Cancer
- UV radiation
- Skin cancer rates
Chemicals:
- Agent Orange
- Nicotine
- Benzene
- Asbestos
DP6 “explain how an understanding of the source of variation in organisms has
provided support for Darwin’s theory of evolution by natural selection”
 One of the foundation pillars for the theory of evolution is the variation that
occurs among individual members of a species. The basis of this variation is
the genetic makeup of the individuals in a species. It is this variation that
selection acts upon. Mutation of DNA provides a source of new variations
thus supporting Darwin's theory of evolution.
DP7 “describe the concept of punctuated equilibrium in evolution and how it
differs from the gradual process proposed by Darwin”
 Punctuated equilibrium differs from Darwin's gradual evolution in that
evolution is seen as long periods where there is little change in organisms,
followed by a shorter period where there are rapid changes. Evolution is a
sudden process rather than slow gradual change. The evidence for this comes
from the fossil record where there are mass extinctions of organisms
followed by the appearance of new species.
SC DP1 “perform a first-hand investigation or process information from secondary
sources to develop a simple model for polypeptide synthesis”
You could choose to perform a first hand investigation using beads and plasticine to
model polypeptide synthesis. Include in your model the transfer of information from
DNA to messenger RNA (mRNA). You will also need to make a model of transfer RNA
and of several amino acids. Alternatively, you could process information from an
animation, such as those indicated below. When doing this activity, evaluate the
relevance of first-hand and secondary information in relation to the understanding
of the process of polypeptide synthesis.
SC DP2 “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”
Beadle and Tatum used bread mould to investigate nutritional mutations. Using Xrays, they produced mould that was unable to produce a specific amino acid. The
mould was unable to grow unless the amino acid was added. They showed that
genes controlled biochemical processes. Their hypothesis was that for each gene
there was one enzyme or protein. The enzymes that they studied consisted of one
polypeptide but many enzymes consist of chains of polypeptides. Therefore, the
hypothesis has been changed to the “one – gene one – polypeptide” hypothesis.
SC DP3 “process information to construct a flow chart that shows that changes in
DNA sequences can result in changes in cell activity”
SC DP4 “process and analyse information from secondary sources to explain a
modern example of ‘natural’ selection”
Some organisms, such as bacteria and insects, produce large numbers of offspring.
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. This has been the story for antibiotics since they were first used. The initial
use of an antibiotic results in good protection from bacteria. Over time the chemicals
become less and less effective. A case study provides a good example of how natural
selection occurs. A similar situation occurs in the resistance of insects to insecticides.
Selecting those individuals that are able to survive and reproduce increases the
frequencies of those genes in the population. This is “survival of the fittest” where
the fittest are those that have a natural resistance to a selecting factor, which in the
case of bacteria described above, is antibiotics.
SC DP5 “process information from secondary sources to describe and analyse the
relative importance of the work of:
o James Watson
o Francis Crick
o Rosalind Franklin
o Maurice Wilkins
in determining the structure of DNA and the impact of collaboration and
communication in scientific research”
James Watson – Worked together with Crick in finding the Double Helix
Francis Crick – Worked together with Watson in finding the Double Helix
Maurice Wilkins – Worked together with Franklin with photographs – stole Franklins
Photo 51
Rosalind Franklin – Worked together with Wilkins with photographs
The communication between Watson/Crick and Wilkins was important because
without Wilkins giving them the photograph their timeframe in discovering the
double helix would be extremely held back. Also if Franklin and Wilkins were working
in the same place and they both knew what each other worked on, so if Wilkins
never worked with Franklin, he never would have found the photograph to give to
Watson/Crick and they progress would have been delayed.
5. Current reproductive technologies and genetic engineering have the
potential to alter the path of evolution.
DP1 “identify how the following current reproductive techniques may alter the
genetic composition of a population:”
o artificial insemination
o artificial pollination
o cloning
In the case of all the technologies mentioned, the donor gametes or body cells have
been carefully selected for predetermined characteristics – or artificially selected. In
most cases, one exemplary donor contributes all the genetic material and this results
in uniform offspring. Over generations, genetic variability within the species has
been reduced.
DP2 “outline the processes used to produce transgenic species and include
examples of this process and reasons for its use”
 Transgenic organisms contain a gene (transgene) from another species. This
is acheived through recombinant DNA technology. Recombinant DNA
technology manipulates DNA by the use of restriction enzymes, ligases and
PCR (polymerase chain reaction). Restriction enzymes are used to cut DNA in
specific places. These enzymes are also known as gene scissors or gene
shears. Different restriction enzymes cut DNA in specific parts. The cut ends
are known as 'sticky ends'. Ligases are used to repair and strengthen DNA
especially after it has been cut by restriction enzymes. PCR is used to produce
many copies of the recombinant DNA formed by the previous processes.
 Once the recombinant DNA is produced there are processes used to insert
the DNA into the host species. These processes include microinjection, Ti
plasmid insertion, gene gun and electroporation.
 In microinjection a fine glass needle is used to insert the recombinant DNA
into the nucleus of the host cell.
 Ti (tumour inducing) plasmid insertion uses a bacterium called Agrobacterium
tumefaciens. These bacteria produce crown gall in plants by inserting some of
their own DNA into the host DNA causing the plant to produce a gall in which
the bacteria live. The ability of the bacteria to insert DNA is used to transfer
DNA into the host species.
 The gene gun blasts small metal pieces coated with DNA into the nucleus of
the host cell.
 Electroporation uses electric pulses to create small pores in the nuclear
membrane through which DNA is inserted.
 Examples of transgenic species are genetically engineered salmon which have
the gene coding for the protein, bGH (bovine growth hormone), and potato
plants which have a pea gene for lectin inserted.
DP3 “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”


Reproductive technologies, such as cloning, and the engineering of transgenic
species have the potential to both increase and decrease genetic diversity.
By moving genes from species to species, the genetic diversity is being
increased. Crops, such as rice, have been genetically engineered to suit a
particular climate and topography, making then resistant to herbicides and
pesticides commonly used in a particular region.
Transgenic animals present greater problems with lower success rates so far.
One important use is seen to be the preservation of numbers of endangered
species. The first cloned endangered mammal was a guar (an endangered
wild ox from SE Asia), but unfortunately it did not survive. It is hoped that
reproductive technologies such as cloning and sperm and embryo banks can
be used to preserve stocks of threatened species.
SC DP1 “process information from secondary sources to describe a methodology
used in cloning”
Recently, plants have been cloned using tissue culture propagation. Tissue from the
roots is taken and the root cells separated. These cells are then grown (cultured) in a
nutrient-rich medium where they become unspecialised. The unspecialised cells are
called calluses. After treatment with the appropriate plant hormones, the calluses
are able to develop into seedlings, that go on to grow into fully mature plants. These
plants are genetically identical to the original ‘parent’ plant. Rare orchids have been
cultured and grown in this manner. A more recent example, has been the cloning of
tissue from the Wollemi Pine. This rare pine, thought to be extinct but now has been
discovered in the Blue Mountains region of NSWand successfully cloned. These
cloned offspring are being cultivated in the Royal Botanic Gardens in Sydney and sold
to the public for planting in gardens. Thus, the species, which has few numbers in
the wild, can be preserved.
In animals, progress in cloning species has not been as rapid. Current techniques
require an unfertilised egg to act as a ‘host’ for genetic material from a specialised
cell. The donor egg has had its nucleus physically removed, and the nucleus from a
cell of the species to be cloned is inserted. An electrical stimulus is used to fuse the
nucleus with the egg cell and to stimulate cell division. At a certain stage in cell
division, the embryo is introduced into a surrogate mother where it continues its
development. When born the clone is genetically identical to the animal that
donated the original nucleus. Cloning of animals was first performed with tadpoles
by John Gurdon in the 1970’s. The tadpoles did not survive to grow into adult frogs.
Dolly the sheep was the first successfully cloned mammal in 1997. Since then, other
species have been cloned.
SC DP2 “analyse information from secondary sources to identify examples of the
use of transgenic species and use available evidence to debate the ethical issues
arising from the development and use of transgenic species”
Some ethical issues arising from the development and use of transgenic species
Transgenic organisms are those that have DNA derived from another species
incorporated into their genetic complement. This is done by genetic engineering
techniques. Both plants and animals have been genetically modified to create
‘improved’ strains of a particular species.
The following are two examples:
Genetically engineered salmon:
The gene coding for the protein, bGH (bovine growth hormone), is incorporated into
the genes of salmon.
 Outcome – larger, faster growing fish
 Evaluation – Possible farmed source of fish as food. However, the fish are
kept in ponds that offer no escape to the wild because there is much concern
that they will upset or destroy natural ecosystems.
Potato plants:
A pea gene for lectin has been incorporated into potato plants.
 Outcome – protection against insect attack. Lectin is a protein which
interferes with digestion in insects. It is termed an ‘antifeedant’.
 Evaluation – As potatoes are a staple food source for many populations
throughout the world, it is important to maintain and increase production.
Protection against insect attack improves the success of growing potatoes.
Concerns exist about controlling the ‘escape’ of these transgenic potatoes
into the wild as the technology is only recent and long-term impacts on the
environment have yet to be observed or evaluated.