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HSC YEAR 12 BIOLOGY
BLUEPRINT OF LIFE
First I would like to say that this document should be used as a guideline in building your
own syllabus answers, rather than copied and memorised. The latter strategy will work
against you in exams...
Outline the impact on the evolution of plants and animals of:
o changes in physical conditions in the environment
o changes in chemical conditions in the environment
o competition for resources
Changes in the physical conditions in the environment
These include natural conditions such as temperature and water availability.
Pepper moths vary in colour, either pale or dark. Pale moths survive and dominate the
population when the trees remain unpolluted due to their camouflage. However when trees
darken due to pollution, conditions becomes favourable for dark moths, which survive and
dominant the population over time.
Changes in the chemical conditions in the environment
These include the use of DDT and changes in salt level.
DDT was used to kill off mosquitoes in attempt to control malaria. However some
mosquitoes had variations that arose from mutations. Such variation includes resistance to
DDT. These mosquitoes survived the spraying, to reproduce, passing on its genetic
resistance to its off springs. These resistant mosquitoes soon dominate the population and
DDT lost its effectiveness.
Competition for resources can occur within and between species
Resources include food, water, space and mates.
Competition for resources can have an evolutionary impact if resources are limited. Unfit
organisms will face extinction in favour of the species with better adaptive variation. E.g.
feral cats and foxes in Australia are extinct due to competition with introduced species.
Describe, using specific examples, how the theory of evolution is supported by the
following areas of study:
o palaeontology, including fossils that have been considered as transitional forms
o biogeography
o comparative embryology
o comparative anatomy
o biochemistry
Palaeontology is the study of fossils. Fossils are preserved remains of dead organisms.
Fossils show gradual evolutionary changes over time, from simple to very complex
organisms. Fossils of the horse show a gradual increase in size, reduced number of toes
and larger cheek span. Transitional forms are fossils of organisms that are intermediate
forms between major groups of organisms. This shows evolutionary changes. E.g. the
Archaeopteryx was an organism with reptilian teeth and tail but also had feathers of birds.
This supports the evolution of reptiles to birds.
Biogeography is the study of distribution of organisms. These patterns of distribution show
that species that has originated from the same ancestor, when isolated had become new
species. E.g. the unique fauna of Australia. This gives support for theory of evolution.
Comparative embryology shows the embryos of different species in its early stages shows
many similarities. Humans, fish, cats all have gill slits in their early stages. This is evidence
for common ancestry and is a support for theory of evolution.*
Comparative anatomy shows that basic structures of different organisms are very similar
while they perform different tasks. E.g. the forelimbs of humans, cats, and whales. They are
similar in structure, one bone in the upper part, two in the lower limb, leading to the five digits.
(Pentadactyl limb)This suggests that these homologous structures have been derived from a
common Ancestor, supporting the theory of evolution.
Biochemistry is the study of DNA, RNA and amino acid sequencing. This study shows that
many organisms process similar basic molecules derived from a common Ancestor,
supporting the theory of evolution.
(*The fact that different organisms shared common Ancestor shows all organisms have
developed from previous organisms and that all living things from all domains of life have a
common ancestor in some initial form of primitive life. I.e. evolution has taken place over
time.)
Explain how Darwin/Wallace’s theory of evolution by natural selection and isolation
accounts for divergent evolution and convergent evolution
Natural selection is a gradual process where environmental pressures act upon gene pool of
populations, selecting those individuals with the best adaptive variations to survive,
reproduce and slowly have their favourable characteristics dominate the population over
time. Unfit organisms that do not reproduce, has it genes removed from the gene pool.
Convergent evolution is where distantly related organisms evolve to be similar over time due
to similar environmental pressures. I.e. dolphin and sharks are similar in that they both have
streamline bodies. Here Natural selection acted upon different genetic material but selected
similar adaptive variations due to similar environments. Hence these organisms evolve to be
very similar over time.
Divergent evolution is where closely related organisms evolve to be very different over time
due to isolation in different environments. I.e. Darwin's finches have various sized beaks due
to different environmental resources. Here Natural selection acted upon similar genetic
material but selected different adaptive variations due to different environments. Hence
these organisms evolve to be very different over time.
Outline the experiments carried out by Gregor Mendel
Mendel worked with garden pea plants to investigate the nature of inheritance. He identified
7 traits in the pea plant that had alternative forms. He then crossed pure breeding plants that
had alternative forms of each trait (e.g. tall with short plants) to form the F1 generation where
only the dominant trait appeared in the phenotype. (E.g. only tall plants). He then self
fertilised the F1 generation to produce the F2 generation where the recessive trait
reappeared in the ratio of 1:3 (recessive: dominant)
He concluded that:
1. Inheritance is not simply a blend of characteristics.
2. Inheritance is controlled by a pair of factors
3. There was a dominant/ recessive relationship among the factors.
4. Factors are separated when sex cells are formed. (Mendel's law of segregation)
5. Offspring receives one factor randomly from each parent during fertilisation. (Mendel's law
of independent assortment)
Mendel was successful because:
1. He used large number of pea plants and repeated the experiments many times to ensure
statistical accuracy, and reliability of his results.
2. Pea plants were easy to grow and reproduced quickly, this allow him to collect results
within his life time.
3. He controlled the fertilisation process by transferring pollen by hand, and then covering
the flowers with plastic bags and he also made sure he used pure breeding plants in the
start
4. He studied many easily identified traits that had alternative forms, one at a time.
5. He used mathematics to analyse his results.
His work was ignored because:
Mendel was a monk and not a part of the scientific community
Not much was known about genetics at the time
He had only presented his work to very few people
Distinguish between homozygous and heterozygous genotypes in monohybrid
crosses
Heterozygous and homozygous refers to the combination of alleles in the genotype. E.g. if
plant is homozygous for plant height its phenotype is either tall (TT genotype) or short (tt
genotype) or if the plant is heterozygous for height, its phenotype is tall (genotype Tt)
Distinguish between the terms allele and gene, using examples
A gene is a part of the chromosome; it is a short length of DNA that codes for a particular
characteristic. Alleles are alternatives of a gene, the variations that a gene may have. E.g.
there is a gene for heights in humans; the alleles are tall (T) or short (t).
Outline the roles of Sutton and Boveri in identifying the importance of chromosomes
Boveri worked with sea urchin eggs to show that not all chromosomes of all organisms were
the same. He also showed that a full set of chromosomes was needed for normal growth
and reproduction.
Sutton worked with grasshoppers to show that chromosomes were distinct objects with
distinct structures. He explained that the characteristics and behaviours of homologous pairs
of chromosomes were independent and was the mechanism for Mendel's experimental
observations and result.
From the results they gathered, both scientists concluded that chromosomes were carriers of
genes.
Describe the chemical nature of chromosomes and genes
Chromosomes consist of 60% protein called histone and 40% DNA. Chromosomes are
carrier of genes which are short lengths of DNA and thus have the same composition as
DNA. DNA consists of joining nucleotides molecules each made up of connecting
nitrogenous bases, deoxyribose sugars, and phosphates.
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
DNA is a double stranded nucleic acid twisted into a helix. It is shaped like a twisted ladder.
Join phosphate groups and deoxyribose sugars form the backbone of the ladder. While
complementary nitrogenous base pairs (a-t c-g) joining to each other and sugars via
hydrogen bonds forms the rugs of the ladder. A unit of phosphate, sugar and base is known
as nucleotide.
Explain the relationship between the structure and behaviour of chromosomes during
meiosis and the inheritance of genes
Meiosis is the nuclear division of diploid cells to form sex cells used in reproduction. Initially
the chromosomes replicate. In the first division, the homologous chromosomes pair up and
may exchange chromosomal segments. This is crossing over and it results in new
combination of alleles on the chromosomes. Random segregation follows, where one of
each pair of homologous chromosomes moves independently and randomly into a new cell,
allowing many possible combinations of genes in daughter cells. In the second division the
chromosomes separate into single strands to form 4 genetically different haploid daughter
cells.
Explain the role of gamete formation and sexual reproduction in variability of offspring
Outline ways in which the environment may affect the expression of a gene in an
individual
Gamete formation through meiosis results in halving the chromosome number in cells
(diploid to haploid). Sexual reproduction unites gametes to form a new haploid organism.
This organism is not genetically identical due to:
Crossing over during meiosis - where pairs of homologous chromosomes exchange
chromosomal segments. This results in new combinations of alleles on the chromosomes.
Random segregation during meiosis - where one of each pair of homologous chromosomes
moves independently and randomly into a new cell, allowing many possible combinations of
genes in daughter cells.
Sexual reproduction - more variations arise due to the fact that the gametes involved in the
fertillisation are determined by chance.
Environment - the environment can affect the phenotype expressed by masking or
enhancing a gene from revealing. Identical gene does not always result in identical
phenotypes. e.g. 2 identical height genes in identical twins do not mean both individuals will
have the same height due to variations in their diets and health. Some plants such as
hydrangeas can produce different coloured flowers depending upon the pH of the soil.
Difference in pH changes the availability of aluminium ions present in the soil and this
causes the colour change. The environment may also contain mutagens that can cause
changes in chromosome number and changes in DNA base sequence, inducing new alleles
in organisms.
Explain how an understanding of the source of variation in organisms has provided
support for Darwin’s theory of evolution by natural selection
Natural selection is a gradual process where environmental pressures act upon gene pool of
populations, selecting those individuals with the best adaptive variations to survive,
reproduce and slowly have their favourable characteristics dominate the population over
time. Unfit organisms that do not reproduce, has it genes removed from the gene pool.
The study of genetics has showed that variations in a population arise from:
- The formation of gametes, where the crossing over and random segregation of
homologous pairs of chromosomes create new combination of genes and alleles in the four
daughter cells.
- The process of sexual reproduction where the gametes involved in fertilisation are
determined by chance
- The environmental effects that can enhance or mask a gene from revealing
- Mutagens that can cause changes in chromosome number and changes in DNA base
sequence
Natural selection can only occur when there are variations among populations. Those with
favourable variations survive. Hence these sources of variation support the theory of natural
selection.
Describe the inheritance of sex-linked genes, and alleles that exhibit co-dominance
and explain why these do not produce simple Mendelian ratios
Explain the relationship between homozygous and heterozygous genotypes and the
resulting phenotypes in examples of co-dominance
Sex-linked genes allow a trait to appear more often in one sex than the other. An example is
red green colour blindness in humans. This gene is carried on the X chromosome and has
no corresponding gene on the Y chromosome. Hence one allele would cause colour
blindness in males, while females needs two. Thus there is a higher probability of males
being colour blinded than females. Sex-linked gene does not display simple Mendelian ratios
since males only have one X chromosome and sex linked genes are not carried on
autosomes.
Co-dominance occurs when both alleles of a heterozygous genotype are expressed in the
phenotype. Hence no allele is dominant and no allele is masked. An example is the human
blood group. there are 3 alleles A, B and O. O is recessive to both A and B, however A and
B are co-dominant and a genotype of AB will form the blood group AB. another example is
found in cattle, cattle may have white or red fur, however red and white are also co-dominant
and a genotype of RW (red and white) will produce a phenotype of roan. Co-dominance
does not show simple Mendelian ratios since there is no dominant/recessive relationship
among the alleles.
Describe the work of Morgan that led to the understanding of sex linkage
Thomas Hunt Morgan worked with fruit flies and identified sex linkage. He crossed white
eyed males with red eyed females to produce the F1 generation where only red eyed flies
appeared. When he interbreeds the F1 generation to produce the F2 generation white eyed
flies reappeared. However these white eyed flies were all males. This suggested that the
white eye gene was carried on the X chromosome and has no corresponding gene on the Y
chromosome. Hence only one allele on the X chromosome would create white eyes in males
while 2 alleles are needed for females. This results in more males with white eyes than
females. This is known as sex linkage.
Describe the process of DNA replication and explain its significance
1. DNA helix is unwind by enzyme helicase
2. The DNA strand unzips forming 2 single strands where the complementary nitrogenous
base pairs are separated.
3. New complementary nucleotides in the nucleus attaches to the 2 single strands to form 2
identical DNA strands. This is catalysed by DNA polymerase.
DNA replication is of major importance since it allows large amount of genetic material to be
copied. Thus it initiates the nuclear division of cells in meiosis and mitosis. Thus DNA
replication is directly responsible for growth and repair of somatic cells and creating
genetically different gametes for sexual reproduction and creating adaptive variations in the
population. This ultimately ensures the survival of species and maintenance of biodiversity
on Earth, without DNA replication all life on earth would cease to exist.
Outline, using a simple model, the process by which DNA controls the production of
polypeptides
Explain the relationship between proteins and polypeptides
This involves 2 stages
Transcription - the DNA helix is unwind by enzyme helicase and partly unzips. It then
transcribes its DNA base code onto a mRNA. The mRNA then migrates from the nucleus to
the cytoplasm and attaches to a ribosome.
Translation - the tRNA has an amino acid attached to every one of its anti codons. The tRNA
then attaches to the mRNA according to matching codons and anti codons. Once attached,
the amino acids on the tRNA will form an amino acid chain with a sequence as instructed by
the DNA. An enzyme then acts upon this amino acid chain to form a polypeptide. One or
more of these polypeptide chains folded forms proteins.
Amino acid chains make polypeptides, one or more polypeptide chains folded makes
proteins.
Explain how mutations in DNA may lead to the generation of new alleles
Mutations are changes in the DNA information on the chromosomes. Mutations arise from
exposure to mutagens and incorrect DNA replications (that does not get repaired, most do)
in meiosis and mitosis, transcriptions and translations. There are 2 types of mutations,
change in chromosome number and change in DNA base sequence. These results in new
polypeptides formed since it’s made as instructed by the DNA base sequence. This new
polypeptide forms new proteins which may change cellular structure and function and may
alter enzyme activity. This leads to new alleles and variations. If this mutation is not lethal
and is advantageous and has occurred in sex cells, it may be passed on to off springs and
slowly dominate and create a generation of new alleles in a population over time.
Discuss evidence for the mutagenic nature of radiation
A mutagen is any agent that causes a mutation. A mutation is a change in DNA information
on the chromosomes. This leads to new alleles and variations. There variations may be
lethal or non lethal or even advantageous. However most are lethal. Examples of mutagens
are x-rays, atomic bomb radiation, ultraviolet radiation. There are many evidences of
mutagenic effects of these radiations. Early scientist that worked with x-rays when it was first
discovered died of cancers such leukaemia. After atomic bombs were dropped in Hiroshima,
the deaths due to cancers in the area increased. The high incidence of skin cancer in
Australia where people are constantly exposed to UV rays from the sun is also evidence.
However mutagens have also increased our scientific understanding. Such as when Beadle
and Tatum used x-rays to create bread mould which leads to the "One gene, one
polypeptide" hypothesis. These evidence shows that mutagens are usually dangerous and
fatal. It should be handled with care or avoided entirely.
Describe the concept of punctuated equilibrium in evolution and how it differs from
the gradual process proposed by Darwin
The theory of punctuated equilibrium shows that there are short periods of rapid evolutionary
change followed by long periods of no change. This is depicted by fossil evidences of mass
extinction followed by a rise of new organisms over a short period.
It differs from Darwin's theory of gradual evolution where organisms evolve gradually over
time according to the process of natural selection where the fittest survive. The organism are
constantly evolving and changing at a slow rate. Evolution of the horse as depicted by fossil
evidence supports this.
Identify how the following current reproductive techniques may alter the genetic
composition of a population:
o artificial insemination
o artificial pollination
o cloning
Outline the processes used to produce transgenic species and include examples of
this process and reasons for its use
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
Current reproductive technologies used by humans, aims to alter the gene pool of different
organisms to improve their characteristics for human uses and purposes. These
technologies include:
Artificial insemination - Sperm from males with desirable traits are collected and placed
inside females' uterus to unite with females' eggs to cause fertilisation. The growth of the
offspring then occurs as normal inside the female. The offspring is likely to display the
desired traits.
Artificial pollination - Pollen from plants with desirable traits are collected and are dusted
over female stigmas by hand to cause fertilisation. Plastic bags are then used to control the
process. The offspring is likely to display the desired traits.
Cloning - this involves cutting and grafting in plants. In animals, the nucleus of a somatic cell
from a chosen individual is isolated and inserted into an enucleated egg cell. This is then
implanted into a surrogate where normal growth occurs. As a result the offspring will be
genetically identical to the chosen individual.
Production of transgenic organisms - this involves transport of desired genes from one
organism to another totally different organism. When a desired gene is identified and located,
the same restriction enzyme is used to cut the 2 DNA strands of the 2 different organisms.
Then the enzyme ligase is used to repair and recombine the sticky ends of the cut DNA. This
new modified gene is then inserted into a cell of the organism by instruments such as a gene
gun. The organism will display the desired gene as a result. Transgenic species can be
similarly produced by using bacteria that can infect plants with its DNA. The DNA is modified
to include desired genes.
By genetically modifying plants, we can grow plants such as BT cotton which can produce its
own natural pesticide and therefore are pest resistant without the use of human made
pesticide. BT cotton therefore produce higher yield at lower cost, however resistance to BT
may soon occur. Salmons can be modified to include the bGH gene which allows salmons to
grow larger, faster. These results improve econoimical values, increase food production for
humans and reduce pollution.
The genetic information in these reproductive technologies are often used repeatedly on
large number of specimens, to introduce predetermined characteristics that greatly increase
chances of survival. This results in uniform off springs dominating the population over nonmodified individuals, and the lost of genetic variability over time.
The lost of genetic variations renders entire populations susceptible to the same disease,
predator or natural changes in the environment. This drastically increases the risk of reduced
population and lost of biodiversity. The effects of these organisms as food for humans are
also unknown. There is also risk of contamination between genetically modified and
unmodified species which may further accelerate the lost of biodiversity.
The production of transgenic organisms may initially increase the biodiversity as it introduces
new characteristics into organisms. However if only one particular transgenic variety is used,
over time it will most likely dominant the population with the advantages it has with their
transgenic characteristics and again lost of genetic variability will result. Cloning has the
potential to increase the gene pool by reviving extinct organisms such as the Tasmanian
tiger.
These reproductive technologies should be limited in both number and location to reduce
risks, and its progress should be monitored at all times to prevent negative effects.
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