VCE Unit 3 & 4 biology - Home



POPULATION GENETICS

Question 1

Genetic drift is:

a) Most evident in large populations

b) The gene flow between populations

c) Random changes in the gene pool of a population

d) The gradual change in phenotypic frequency resulting from natural selection

Question 2

A population of birds was described as being in genetic equilibrium for a gene locus determining beak colour. It would be reasonable to suggest that:

a) There was gene flow occurring between this population and an adjacent population

b) There was selection against one of the beak colours in this population

c) The birds in the population were mating at random

d) The population was small

Question 3

The variation in allele frequencies between several isolated populations can be due to genetic drift. Genetic drift is likely to be observed when:

a) There is gene flow

b) The mutation rate is high

c) There are strong selective pressures

d) A population is reduced to a few individuals

Question 4

The frequencies of the phenotypes of the MN blood group were measured in a European population. Of 100 individuals, 40 were blood type M, 20 were blood type MN and 40 were blood type N. From this data it is possible to conclude that:

a) The frequency of the N allele is 0.3

b) The frequency of the M allele is 0.5

c) There are 60 M alleles in this population

d) There is a total pool of 100 alleles at this locus for this population

Question 5

In some autosomal recessive conditions in humans, the homozygous recessive genotype results in death before reproductive age. Despite this the allele for the recessive trait is maintained in the population. Maintenance of this allele in the population is most likely the result of:

a) Mutation

b) Migration between populations

c) The heterozygote being biologically fitter than either of the homozygous genotypes

d) Individuals with the homozygous dominant genotype leaving more offspring in each generation

Question 6

Genetic drift

a) Is the result of selection

b) Only occurs in large populations

c) Results from a sudden increase in population size

d) Is a chance loss of an allele from a population

Question 7

In phlox plants a gene locus produces the enzyme alcohol dehydrogenase. There are 2 alleles at this locus A1 and A2, each producing a different form of the enzyme. A heterozygote can produce both forms of the enzyme. Fifty plants were samples to see which enzyme was produced. The results are shown below.

[pic]

From the data above it is possible to conclude that:

a) The total number of A2 alleles is 30

b) The frequency of the A1 allele is 0.3

c) The frequency of the A2 allele is 0.5

d) There are a total of 50 alleles in this population

Question 8

All the alleles in a population are referred to as the:

a) Phenotypic family

b) Proteome

c) Gene pool

d) Genotype

Question 9

The founder effect and bottleneck are examples of:

a) Gene flow

b) Speciation

c) Genetic drift

d) Selection pressures

Question 10

For allele frequencies to remain constant in a population it is essential that:

a) Mutations occur

b) Genetic drift occurs

c) Mating occurs at random in the population

d) There is regular migration into the population

Question 11

Which of the following is true of a mutation that produces an allele that is dominant?

a) It would be expected to cause death

b) It would be expected to spread more quickly through a population than a recessive mutation

c) It could give an observable phenotype in a heterozygous genotype

d) It could give an observable phenotype only in a homozygous genotype

SHORT ANSWER QUESTIONS

Question 1

Explain what is meant by the founder effect in the context of population genetics.

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Question 2

Warfarin is a poison used to control rat populations. The diagram below shows changes in the proportion of rats resistant to warfarin in a particular population, over a period of about 4 years. High levels of warfarin were used on this population during Year 2 but poisoning stopped at the end of this period. Rats are reproductively mature at an age of 3 months and can breed about every 3 weeks.

[pic]

Explain the process which led to the increase in the percentage of resistant rats during year 2

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Using the data in the graph, explain what can be concluded about the selective advantage to a rat of being warfarin resistant compared to being non resistant in an environmental without warfarin.

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Question 3

Rock wallabies, Petrogale lateralis pearsonii, on Pearson Island off the coast of South Australia have had no genetic contact with mainland rock wallabies since they were isolated by rising sea levels at the end of the last glacial period, around 10 000 years ago.

Scientists have taken blood samples from the wallabies and compared the distribution of unique DNA sequences called microsatellites, which are scattered across the wallabies’ chromosomes. These microsatellites give a measure of the population’s genetic diversity, or lack of it. In this case the microsatellite data showed that the Pearson Island population has low genetic diversity.

The scientists concluded that the Pearson Island population of rock wallabies has been through a genetic bottleneck. A genetic bottleneck is an example of genetic drift.

Explain how a genetic bottleneck may lead to a decrease in genetic diversity.

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Despite the Pearson Island rock wallabies’ lack of genetic diversity, the population size has been maintained over many generations. In fact, the wallabies appear to be thriving. Suggest one reason for the wallabies’ success despite the lack of genetic diversity within the population.

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The population of rock wallabies on Pearson Island is most closely related to small populations of rock wallabies in southern Western Australia. Some scientists argue that some individuals from the southern Western Australian populations should be released onto Pearson Island.

Give one reason for this suggestion.

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