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BIOLOGY, M6 2024 HSC 18 MC

The following diagram models a population of glowworms in an isolated cave. The letter \(B\) and \(b\) represent the alleles for a gene in an individual.
 

Which row of the table correctly identifies the process and reason for the change in the gene pool?

\begin{align*}
\begin{array}{l}
\rule{0pt}{2.5ex}\textbf{}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex} \ \rule[-1ex]{0pt}{0pt}& \\
\rule{0pt}{2.5ex}\textbf{A.}\rule[-1ex]{0pt}{0pt}\\
\textbf{}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{B.}\rule[-1ex]{0pt}{0pt}\\
\textbf{}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{C.}\rule[-1ex]{0pt}{0pt}\\
\textbf{}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{D.}\rule[-1ex]{0pt}{0pt}\\
\textbf{}\rule[-1ex]{0pt}{0pt}\\
\textbf{}\rule[-1ex]{0pt}{0pt}\\
\end{array}
\begin{array}{|l|l|}
\hline
\rule{0pt}{2.5ex}\textit{Process} \rule[-1ex]{0pt}{0pt}& \textit{Reason} \\
\hline
\rule{0pt}{2.5ex}\text{Gene flow} & \text{Change in frequency} \\
& \text{of the \(b\) allele due to a mutation} \rule[-1ex]{0pt}{0pt}\\
\hline
\rule{0pt}{2.5ex}\text{Genetic drift} & \text{Change in frequency} \\
& \text{of the \(b\) allele due to random events} \rule[-1ex]{0pt}{0pt}\\
\hline
\rule{0pt}{2.5ex}\text{Gene flow} & \text{Introduction of more \(b\) alleles due } \\
& \text{to new members moving into the population} \rule[-1ex]{0pt}{0pt}\\
\hline
\rule{0pt}{2.5ex}\text{Genetic drift} & \text{Introduction of more \(b\) alleles due } \\
& \text{to this allele being more advantageous} \rule[-1ex]{0pt}{0pt}\\
\hline
\end{array}
\end{align*}

Show Answers Only

\(B\)

Show Worked Solution

→ The diagram shows genetic drift, where the \(b\) allele becomes fixed in the population over time through random chance events in a small, isolated population (as indicated by the cave setting).

→ The context of an isolated cave means that the changes could not have been the result of natural selection or gene flow from outside populations.

\(\Rightarrow B\)

♦♦ Mean mark 33%.

BIOLOGY, M6 2024 HSC 9 MC

The diagram shows a section of a chromosome in an insect. It represents three genes amongst non-coding DNA. The crosses mark locations of four separate mutations.
 

Which location could produce a new allele for eye colour?

  1. \(P\)
  2. \(Q\)
  3. \(R\)
  4. \(S\)
Show Answers Only

\(C\)

Show Worked Solution

→ Since \(R\) is located within the gene region for eye colour, a mutation at this location could alter the DNA sequence of this gene and produce a new allele for eye colour,.

→ Mutations at other locations (\(P, Q\) and \(S\)) are either in non-coding regions or different genes.

\(\Rightarrow C\)

BIOLOGY, M6 2020 VCE 27*

Tasmanian devils (Sarcophilus harrisii) were originally broadly distributed across Australia. When sea levels rose 12 000 years ago, an island, now referred to as Tasmania, was formed. The small number of Tasmanian devils on Tasmania was cut off from the Australian mainland populations. The population in Tasmania showed less genetic variation than the mainland populations. Mainland populations became extinct approximately 3000 years ago.

Over the last 20 years, the total Tasmanian devil population on Tasmania has halved. Many of the deaths have been the result of Tasmanian devil facial tumour disease (DFTD). Scientists have taken some Tasmanian devils that do not have DFTD to mainland Australia to set up a conservation program. The scientists have shown that greater genetic diversity among offspring in this program is observed when the Tasmanian devils are kept in isolated male-female pairs rather than in larger groups.

Giving reasons, describe if the conservation program for Tasmanian devils is an example of

  1. allopatric speciation   (1 mark)

  2. selective breeding   (1 mark)

  3. natural selection   (1 mark)

Show Answers Only

i.    Allopatric speciation – No

→  Involves the formation of new species due to geographic isolation whereas the program focuses on preserving the existing Tasmanian devil species.
 

ii.   Selective breeding – Yes

→ Scientists are intentionally choosing which Tasmanian devils to breed together based on their genetic diversity.
 

iii.  Natural selection – No

→ Natural selection is the differential survival and reproduction based on inherited traits.

→ The program involves intentional breeding decisions by scientists.

Show Worked Solution

i.    Allopatric speciation – No

→  Involves the formation of new species due to geographic isolation whereas the program focuses on preserving the existing Tasmanian devil species.
 

ii.   Selective breeding – Yes

→ Scientists are intentionally choosing which Tasmanian devils to breed together based on their genetic diversity.
 

iii.  Natural selection – No

→ Natural selection is the differential survival and reproduction based on inherited traits.

→ The program involves intentional breeding decisions by scientists.

BIOLOGY, M6 2023 HSC 32

The mountain pygmy possum (Burramys parvus) is restricted to four regions in Australia's alpine zone. The species is listed as critically endangered with less than 2000 adults remaining. The range of the mountain pygmy possum has contracted due to a gradually warming climate.
 

Loss and degradation of these habitats have affected local populations. The graph shows changes in the Mt Buller population following recent bushfires and the introduction of male pygmy possums from Mt Bogong.
 

Evaluate how bushfires and the introduction of males from other locations have affected the population size and gene pool of the Mt Buller pygmy possum population.  (7 marks)

Show Answers Only

→ Environmental factors can play extremely large roles in the population and hence gene pool of the pygmy possums in Mt Buller.

→ This can be seen especially between 1996-2007, where three bushfires throughout those years caused the population to drop from 90 to less than 10. This is because bushfires not only kill individual possums, but also destroy their habitat, reducing shelter, food and water sources for the survivors.

→ This catastrophic drop in population significantly reduced the alleles present in the Mt Buller gene pool. The “new” survivor gene pool would see some alleles potentially disappear while others appear more frequently in individuals.

→ This may have led to genetic drift (bottleneck effect) in this population where the low diversity of alleles in the population led to a further reduction in the population between 2002–2007.

→ To counteract this reduction in population and gene pool size, 6 male possums were introduced from a nearby population in 2007. This was done again in 2012, and despite there being another bushfire in 2011, the population increased to 150 by 2015.

→ The introduction of these males in 2007 almost doubled the known population at the time, but just as importantly diversified the gene pool, an effect helped by the isolation of the two populations.

→ This increase in genetic diversity also improves a species’ ability to adapt to the drier and hotter climates being experienced.

→ It is evident that both the bushfires and the introduction of males played different but very important roles in the population size and gene pool of the Mt Buller pygmy possum population.

Show Worked Solution

→ Environmental factors can play extremely large roles in the population and hence gene pool of the pygmy possums in Mt Buller.

→ This can be seen especially between 1996-2007, where three bushfires throughout those years caused the population to drop from 90 to less than 10. This is because bushfires not only kill individual possums, but also destroy their habitat, reducing shelter, food and water sources for the survivors.

→ This catastrophic drop in population significantly reduced the alleles present in the Mt Buller gene pool. The “new” survivor gene pool would see some alleles potentially disappear while others appear more frequently in individuals.

→ This may have led to genetic drift (bottleneck effect) in this population where the low diversity of alleles in the population led to a further reduction in the population between 2002–2007.

→ To counteract this reduction in population and gene pool size, 6 male possums were introduced from a nearby population in 2007. This was done again in 2012, and despite there being another bushfire in 2011, the population increased to 150 by 2015.

→ The introduction of these males in 2007 almost doubled the known population at the time, but just as importantly diversified the gene pool, an effect helped by the isolation of the two populations.

→ This increase in genetic diversity also improves a species’ ability to adapt to the drier and hotter climates being experienced.

→ It is evident that both the bushfires and the introduction of males played different but very important roles in the population size and gene pool of the Mt Buller pygmy possum population.

BIOLOGY, M6 SM-Bank 25

Over time, the South African cheetah population has suffered drastic reduction due to periodic droughts, disease and hunting. Currently, only small, isolated populations of cheetahs exist in the wild.

Explain, in terms of genetic diversity, why cheetah populations are now on the verge of extinction.  (3 marks)

Show Answers Only

→ The cheetah population has suffered a severe bottleneck. This means that (by chance) certain alleles may be over- or under-represented in the surviving population, and some (potentially ‘fitter’) alleles may have been lost altogether.

→ This reduces genetic variability and means that the small surviving population’s gene pool is not representative of the original population.

→ If the environment suddenly changes, the selection pressures on the cheetahs will also change. Having a limited gene pool may mean the population cannot adapt to the changing conditions and are therefore at increased risk of extinction.

Show Worked Solution

→ The cheetah population has suffered a severe bottleneck. This means that (by chance) certain alleles may be over- or under-represented in the surviving population, and some (potentially ‘fitter’) alleles may have been lost altogether.

→ This reduces genetic variability and means that the small surviving population’s gene pool is not representative of the original population.

→ If the environment suddenly changes, the selection pressures on the cheetahs will also change. Having a limited gene pool may mean the population cannot adapt to the changing conditions and are therefore at increased risk of extinction.

BIOLOGY, M6 SM-Bank 24

In 1950 , the myxoma virus was released into Australian pest rabbit populations to reduce their numbers. The resulting disease, myxomatosis, initially wiped out 95% of the rabbit population; however, it quickly became less effective as a population control measure.

This graph shows the frequency of myxomatosis resistance in Australia's rabbit population from 1949 to 1956.
 

Use evidence from the graph and the principles of natural selection to explain how myxomatosis became ineffective as a population control measure.  (3 marks)

Show Answers Only

→ The introduction of the myxoma virus conferred a selective advantage on the myxomatosis-resistant phenotype.

→ Myxomatosis-resistant rabbits had an increased chance of surviving to reproduce and pass on the trait.

→ This led to an increase in the frequency of this phenotype in the population from approximately 9% in 1950 to approximately 96% in 1953 .

→ After 1953, most of the remaining rabbits possessed the myxomatosis-resistant phenotype, so the disease was no longer effective at reducing rabbit numbers.

Show Worked Solution

→ The introduction of the myxoma virus conferred a selective advantage on the myxomatosis-resistant phenotype.

→ Myxomatosis-resistant rabbits had an increased chance of surviving to reproduce and pass on the trait.

→ This led to an increase in the frequency of this phenotype in the population from approximately 9% in 1950 to approximately 96% in 1953 .

→ After 1953, most of the remaining rabbits possessed the myxomatosis-resistant phenotype, so the disease was no longer effective at reducing rabbit numbers.

BIOLOGY, M6 2014 HSC 33d

The data compare a segment of the eye control gene in mice to the equivalent gene segment in a range of different species. The expression of these genes is necessary for eye development to begin.
 

Note: grey highlighted bases are the same as those in the mouse gene.

  1. With reference to the data in the table, explain why it is possible for different gene sequences to produce the same protein.   (2 marks)

  2. Discuss ONE strength and ONE limitation of using the data shown to determine the evolutionary relationships between these species.   (4 marks)

Show Answers Only

“

Show Worked Solution

i.   Explanation

→ Differences in base sequences can still code for the same amino acid, and therefore the same protein will be produced. This is often referred to as a silent change.

→ A change producing a different amino acid can have no effect on the protein if the amino acids are chemically similar. For example leucine and isoleucine are so similar that a change in DNA sequence resulting in this change will have no effect on the protein it codes for. This is called a neutral change.


♦♦ Mean mark (i) 40%.

ii.   Strengths

→ Despite having different sequences, each polypeptide chain/protein it is a part of will go on to initiate eye development.

→ This provides evidence that a once common ancestor had the eye development gene similar to that of all species, providing evidence of their close ancestry.

→ The average rate of mutation can also be used as a measure of time since divergence from the common ancestor. For example, species 2 may have more recently diverted as it has a genetic similarity of 85% when compared to species 4, which only has 71.66% similarity.
  

Limitations

→ The study only shows the relationship of one gene which is very small in comparison to the whole genome. This is a weak comparison as the rest of the genome may have intense variation and just studying this gene could provide false information.

→ Studying only one gene also increases the risk of encountering back mutations, mutations of a variation which revert back to the original sequence, making the species seem more closely related. This can also give false information about evolutionary relationships and ancestry.


♦♦ Mean mark (ii) 41%.

BIOLOGY, M6 2014 HSC 7 MC

Which of the following is essential in any model of natural selection?

  1. High reproductive rates
  2. Random selection of prey
  3. A population of predators
  4. Differences in the population
Show Answers Only

`D`

Show Worked Solution

→ For natural selection to be selective, there must be distinctive characteristic differences within the population which allows certain individuals to be favoured.

`=>D`

BIOLOGY, M6 2019 HSC 26

The map shows the percentage of adult indigenous populations able to digest lactose.
 

The ability to digest lactose is due to the presence of an enzyme (lactase) which can metabolise the sugar (lactose) present in milk. The gene responsible for producing lactase is usually permanently switched off at some time between the ages of 2 and 5 years. However, some people remain able to digest lactose throughout their lives.

With reference to evolution and DNA, provide possible reasons for the distribution shown in the map.   (5 marks)

Show Answers Only

→ The ability to digest lactose is most likely due to a mutation where the gene is not shut off after age 5, and the body continues to produce lactase.

→ The differentiation in the graph above can also be viewed as the frequency of this mutation in certain areas.

→ In areas such as Europe, where over 90% of the adult indigenous population can digest lactose, this mutation is highly prevalent, suggesting it may have played a role in survival advantage.

→ In these areas, milk may make up a high portion of the diet and therefore the ability to digest lactose would prove advantageous and the resulting selective pressure would see it passed on (natural selection).

→ The opposite is true when looking at countries such as Australia where < 20% of indigenous adults can digest lactose.

→ We can deduce that milk is not essential to their traditional diet as the mutation is negligible and not passed on (i.e. it doesn’t constitute a survival advantage).

Show Worked Solution

→ The ability to digest lactose is most likely due to a mutation where the gene is not shut off after age 5, and the body continues to produce lactase.

→ The differentiation in the graph above can also be viewed as the frequency of this mutation in certain areas.

→ In areas such as Europe, where over 90% of the adult indigenous population can digest lactose, this mutation is highly prevalent, suggesting it may have played a role in survival advantage.

→ In these areas, milk may make up a high portion of the diet and therefore the ability to digest lactose would prove advantageous and the resulting selective pressure would see it passed on (natural selection).

→ The opposite is true when looking at countries such as Australia where < 20% of indigenous adults can digest lactose.

→ We can deduce that milk is not essential to their traditional diet as the mutation is negligible and not passed on (i.e. it doesn’t constitute a survival advantage).


♦♦ Mean mark 33%.

BIOLOGY, M6 2019 HSC 13 MC

Genetic drift is a gradual change in

  1. the alleles of an individual due to mutation.
  2. allele frequency in a population due to chance.
  3. the genes of a population due to natural selection.
  4. gene frequency in a population due to natural selection.
Show Answers Only

`B`

Show Worked Solution

By Elimination

→ C and D both refer to natural selection, another mechanism of change within a population, but one that caters towards certain phenotypes or genotypes. (eliminate C and D)

→ A does not refer to a population, but the genotype of an individual (eliminate A)

→ Genetic drift is the reduction or change in allele frequency in a population due to a random chance event that does not favour certain individuals for survival (e.g. a natural disaster).

`=>B`


♦♦ Mean mark 38%.

BIOLOGY, M6 2019 HSC 3 MC

The diagram shows the impact of birds feeding on a population of beetles over time.
 

Which of the following accounts for the change in the beetle population?

  1. Mutation
  2. Gene flow
  3. Genetic drift
  4. Environmental pressure
Show Answers Only

`D`

Show Worked Solution

→ The diagram shows the process of natural selection.

→ The environmental pressure of a predator eliminates individuals from a population based on phenotype.

`=>D`

BIOLOGY, M6 2022 HSC 32

Researchers have identified a gene that determines the inflammatory response of lung cells to infection with a virus. An allele of this gene is associated with increased inflammation and increased chance of death from the virus.

The table shows the percentage presence of the allele in people with different ancestries.
 

Explain how mutation, natural selection, genetic drift and gene flow could have led to these differences in the gene pools of populations with differing ancestry.  (7 marks)

Show Answers Only

Mutation

→ A mutation is a mechanism of change which permanently alters DNA, changing genotype and phenotype of the ‘host’.

→ In this case, a mutation has occurred which has altered the gene responsible for the inflammatory response in the lungs in response to a virus, making death more common for people who contract the virus as the gene is now faulty.

→ Other mechanisms of variation such as natural selection, gene flow and genetic drift, are responsible for the allele frequency distribution.
 

Natural selection

→ Refers to the process where selection pressures such as predators, climate, or in this case the lung virus, favour certain individuals, which then means that their alleles can be carried into further generations.

→ It is highly likely that the virus was never present in South Asia, hence the high frequency in South Asian people (60.3%); the allele was negligible.

→ The virus most likely was present in Europe, Africa and East Asia (<15%) and was responsible for almost eliminating the allele in these populations.
 

Gene flow

→ Gene Flow is the movement of alleles into new populations, usually via migration.

→ Interbreeding between the migrated individual in the new population with the allele, in conjunction with processes such as natural selection can cause the allele to be prominent in the new population.

→ The allele could have originated in South Asia, and gene flow may be responsible for the other frequencies, especially in Europe.
 

Genetic drift

→ This occurs when populations experience drastic changes in allele frequencies due to random chance events.

→ These events, such as a natural disaster or re-establishing a new population, can eliminate or change the allele frequency and do not cater towards any genotype. 

→ It is possible genetic drift is responsible for the comparatively high allele frequency in South Asia, or the relatively low frequency in Africa and East Asia.

Show Worked Solution

Mutation

→ A mutation is a mechanism of change which permanently alters DNA, changing genotype and phenotype of the ‘host’.

→ In this case, a mutation has occurred which has altered the gene responsible for the inflammatory response in the lungs in response to a virus, making death more common for people who contract the virus as the gene is now faulty.

→ Other mechanisms of variation such as natural selection, gene flow and genetic drift, are responsible for the allele frequency distribution.
 

Natural selection

→ Refers to the process where selection pressures such as predators, climate, or in this case the lung virus, favour certain individuals, which then means that their alleles can be carried into further generations.

→ It is highly likely that the virus was never present in South Asia, hence the high frequency in South Asian people (60.3%); the allele was negligible.

→ The virus most likely was present in Europe, Africa and East Asia (<15%) and was responsible for almost eliminating the allele in these populations.
 

Gene flow

→ Gene Flow is the movement of alleles into new populations, usually via migration.

→ Interbreeding between the migrated individual in the new population with the allele, in conjunction with processes such as natural selection can cause the allele to be prominent in the new population.

→ The allele could have originated in South Asia, and gene flow may be responsible for the other frequencies, especially in Europe.
 

Genetic drift

→ This occurs when populations experience drastic changes in allele frequencies due to random chance events.

→ These events, such as a natural disaster or re-establishing a new population, can eliminate or change the allele frequency and do not cater towards any genotype. 

→ It is possible genetic drift is responsible for the comparatively high allele frequency in South Asia, or the relatively low frequency in Africa and East Asia.


♦♦♦ Mean mark 32%.

BIOLOGY, M6 2020 HSC 29

Explain how TWO processes that affect the gene pool of populations can lead to evolution.   (5 marks)

Show Answers Only

→ A gene pool is the total genetic diversity of a population. It includes various genotypes and phenotypes which are a result of variability within offspring, the individual and the population. This process as a whole can be referred to as evolution.

 
Gene Flow

→ The movement of alleles in or out of a population, usually as a result of migration.

→ For example, immigration of an animal into a population as a result of environmental pressures or predators can result in the introduction of that animal’s unique phenotype into the gene pool of the population.

 
Genetic Drift

→ The change in allele frequency as a result of a random event.

→ For example, an earthquake or other natural disaster eliminates organisms regardless of their genotype. The remaining individuals will then carry a small sample of the alleles present in the original population, some which might be eliminated.

 
Other answers could include

→ Mutation

→ Natural Selection

→ Sexual reproduction

Show Worked Solution

→ A gene pool is the total genetic diversity of a population. It includes various genotypes and phenotypes which are a result of variability within offspring, the individual and the population. This process as a whole can be referred to as evolution.

 
Gene Flow

→ The movement of alleles in or out of a population, usually as a result of migration.

→ For example, immigration of an animal into a population as a result of environmental pressures or predators can result in the introduction of that animal’s unique phenotype into the gene pool of the population.

 
Genetic Drift

→ The change in allele frequency as a result of a random event.

→ For example, an earthquake or other natural disaster eliminates organisms regardless of their genotype. The remaining individuals will then carry a small sample of the alleles present in the original population, some which might be eliminated.

 
Other answers could include

→ Mutation

→ Natural Selection

→ Sexual reproduction


Mean mark 53%.

BIOLOGY, M6 2020 HSC 10 MC

A farmer intends to artificially inseminate cows with semen from a bull which has been chosen based on characteristics of colour and muscle mass.

The farmer does not know that the bull is heterozygous for a rare recessive allele not previously present in the farmer's cow population.

The introduction of this recessive allele to the population of cows is an example of

  1. gene flow.
  2. genetic drift.
  3. natural selection.
  4. selective breeding.
Show Answers Only

`A`

Show Worked Solution

→ The introduction of the allele in this fashion was a form of gene immigration (gene flow).

→ It is not the result of a random chance event (genetic drift) nor was it selected by breeders or environmental pressures.

`=>A`

♦ Mean mark 50%.

BIOLOGY, M5 2021 HSC 26

Zebra populations are suffering from a reduction in their gene pools due to habitat destruction and increasing isolation. This has led to an increase in the number of offspring born with coat patterns different to that of their parents. An example is shown.

Explain possible reasons for the increase in these offspring.   (4 marks)

Show Answers Only

A reduction in gene flow occurs when populations become smaller and more isolated. This results in the accumulation of mutations and a reduction in the gene pool due to inbreeding.

Many of these mutations are recessive, and the repeat inbreeding expresses these mutations in offspring that receive two copies.

This effect will occur more often as inbreeding increases, with a greater percentage of zebra offspring appearing different from their parents.

Show Worked Solution

→ A reduction in gene flow occurs when populations become smaller and more isolated. This results in the accumulation of mutations and a reduction in the gene pool due to inbreeding.

→ Many of these mutations are recessive, and the repeat inbreeding expresses these mutations in offspring that receive two copies.

→ This effect will occur more often as inbreeding increases, with a greater percentage of zebra offspring appearing different from their parents.

♦ Mean mark 46%.