Populations (A Level only) (AQA A Level Biology)

Exam Questions

2 hours15 questions
1a2 marks

Define the term species.

1b2 marks

Give two examples of sequencing data that can be compared to establish whether or not organisms are of the same species.

1c1 mark

The killer whale, Orcinus orca, has been observed by scientists to live in groups known as ecotypes. Two ecotypes, known as ‘transient’ and ‘resident’ killer whales both live in the North Pacific. 

Although their habitats overlap, the two ecotypes are considered to be different orca populations. Suggest one reason why this might be the case.

1d1 mark

Some scientists believe that resident and transient orca ecotypes, and many other orca ecotypes around the world, should be reclassified as different subspecies.

Suggest one reason why accurate classification of organisms is important.

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2a1 mark

Define the term gene pool.

2b2 marks

The number of times that an allele occurs within a gene pool is known as the allele frequency.

State and explain one reason why the frequency of an allele might change over time.

2c1 mark

Different alleles in a population lead to the presence of different phenotypes. 

State why it is easier to calculate a phenotype frequency than an allele frequency.

2d2 marks

In a population of cattle, 12 individuals are white, 15 are red, and 28 are roan.

Calculate the frequency of the red phenotype.

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3a1 mark

State what the Hardy Weinberg equation is used for.

3b3 marks

The Hardy Weinberg principle states that the genetics of a population will remain constant from one generation to the next provided that certain conditions, or assumptions, are met.  

State three of the assumptions made by the Hardy Weinberg principle.

3c1 mark

One of the Hardy Weinberg equations is given below.

p + q = 1

State what is represented by p in this equation.

3d2 marks

In a population of species X, the frequency of the recessive allele is 0.21.

Use the equation provided in part c) to calculate the frequency of the dominant allele.

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4a2 marks

Figure 1 below shows changes in the frequency of the allele (Hbs) that causes a disorder known as sickle cell disease between 1960 and 2000. 

Figure 1

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Calculate the percentage increase in the frequency of the Hbs allele between 1960 and 2000.

4b2 marks

The Hbs allele is recessive to the normal allele, HbA

Use Figure 1 to calculate the frequency of the HbA allele in 1960. Both Hardy Weinberg equations are provided below.

p + q = 1

p2 + 2pq + q2   = 1

4c2 marks

Heterozygous individuals, with the genotype HbA HbS, effectively have a normal phenotype.


Use a Hardy Weinberg equation provided in part b) and Figure 1 to calculate the percentage of individuals that are heterozygous for sickle cell disease in 1980.

4d1 mark

In order to apply the Hardy Weinberg principle to a population, there are several assumptions that must be made about that population.

Use your knowledge of the Hardy Weinberg principle and information from Figure 1 to state whether or not the Hardy Weinberg principle can be applied to the population in Figure 1. Explain your answer.

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5a1 mark

Define the term allele frequency.

5b2 marks

One of the Hardy Weinberg equations is shown below.

p2 + 2pq + q2 = 1      

State the meaning of the terms p2  and 2pq in the Hardy Weinberg equation.

5c2 marks

Tay Sachs disease is a recessive condition in which the central nervous system is damaged. Although extremely rare in the general population, Tay Sachs is more common within Ashkenazi Jewish communities, affecting 1 in 3500 individuals.

Use the equation provided in part b) to calculate the percentage of the Ashkenazi Jewish population that are carriers of the allele for Tay Sachs disease.

5d2 marks

In the general population 1 in 320 000 individuals are born with Tay Sachs disease.

Calculate how many times higher the frequency of the Tay Sachs allele is in the Ashkenazi Jewish community in comparison to the general population.

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1a2 marks

The anticoagulant rodenticide Rattex (which contains the active ingredient brodifacoum) is used around homes and farms in British Columbia, to kill rats and mice. Brodifacoum inhibits a gene (VKOR) which is involved in reducing vitamin K. This prevents blood clotting factors from being activated resulting in internal hemorrhaging in animals two to three days after consumption. 

As studies had shown that non-target organisms were at risk of poisoning, ecologists collected data to determine the effect Rattex (brodifacoum) could have on the population of domestic chickens. In their investigation the ecologists noted that some chickens were resistant to brodifacoum as they had the allele BR.

Chickens have three possible genotypes:
BRBR resistant to brodifacoum

BRBV resistant to brodifacoum

BVBV susceptible (not resistant) to brodifacoum

Chickens, with the genotype BRBR, require very large amounts of vitamin K or within a few days they will die of internal hemorrhaging. 

The ecologists studied a population of 160 chickens, feeding them a diet containing sufficient concentration of vitamin K. In this population, 36 had the genotype BRBR, 118 had the genotype BRBV  and 6 chickens had the genotype BVBV.

Calculate the actual frequency of the allele BR in this population. Show your working.

1b1 mark

To determine if the use of Rattex (brodifacoum) could have an effect, the diet of the chickens was then changed to include only a small amount of vitamin K. The chickens were also given Rattex. 

How many chickens out of the population of 160 would be likely to die within a few days?

1c3 marks

Scientists found that in a population of chickens not exposed to Rattex, 64% were resistant to the rodenticide (brodifacoum).


Estimate the percentage of chickens that are heterozygous for brodifacoum resistance using the Hardy-Weinberg equation. Show your working.

1d2 marks

If all the susceptible chickens in this population were killed by Rattex, susceptible chickens would still appear in the next generation. 

Use a genetic diagram to explain how.

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2a2 marks

Ecologists studied the shell colour of a population of banded snails (Cepaea nemoralis) at two different sites in a birch woodland. There are two phenotypes, pink and yellow which are determined by a single gene with two alleles. The pink allele (CP) is dominant over the yellow allele (CY).

Explain what is meant by a population. 

2b3 marks

Outline the method ecologists would use to collect sufficient data to determine whether the observable phenotype frequencies for the two shell colours were similar between the two sites in the birch woodland. 

2c2 marks

A  chi squared test was carried out to determine if the observed phenotypic ratio of pink to yellow shell colour was expected (3:1). When the calculated  chi squaredwas looked up in a table it was found to correspond to a probability of more than 0.05.

What conclusion can you draw from this?

2d3 marks

A population of snails sampled from one of the birch woodland sites contained 84% pink shelled snails. 

Use the Hardy-Weinberg equation to calculate the percentage of the snail population that you would expect to be heterozygous for pink shells. Show your working.

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3a1 mark

In a certain species of goat the coat colour is controlled by one gene, this is known as agouti fur. The coat colour may be brown or tan, black or white. The allele for brown, CBis dominant to the other two alleles. The allele for black, CA, is dominant to the allele for white, CW.

Explain what is meant by a recessive allele.

3b3 marks

A cross between two brown-coated goats produced only brown-coated and black-coated goats. Use a genetic diagram to explain why.

3c3 marks

Give three assumptions that must be made when using the Hardy-Weinberg equation.

3d2 marks

In a hilly region in Portugal white-coated goats make up 25 % of the goat population. Assuming the conditions of the Hardy-Weinberg equilibrium apply, calculate the frequency of allele CW in this population. Show your working.

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4a2 marks

In Borneo, the blood type of 300 orangutans were sampled by ecologists. In this population, 81 orangutans had the genotype IAIO, 63 had the genotype IBIO, 153 had the genotype IAIB and 3 had the genotype IOIO

Using the given information, explain the term gene pool.

4b3 marks

Explain what the Hardy-Weinberg principle predicts?

4c2 marks

Calculate the actual frequency of the allele IO

The Hardy-Weinberg equation should not be used in your calculation.

4d1 mark

In another population of 500 orangutans, the frequency of the IO allele was 0.3. 

Determine what the Hardy-Weinberg principle will predict about the frequency of the IO allele after another 5 generations?

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5a2 marks

In Asia, pyrethroids are sprayed insecticides used to kill mosquitoes, to try to control the spread of dengue. Dengue is a virus that is spread by Aedes aegypti mosquitoes. 

The A.aegypti mosquitoes have a gene called voltage-gated sodium channel (VGSC). Scientists studying pyrethroid resistance in mosquitoes discovered that some mosquitoes had an allele of this gene, V1016G minus, which gave them resistance to pyrethroids. The other allele, V1016G plus, did not give resistance.

Scientists investigated the frequency of the V1016G minus allele in a population of A.aegypti mosquitoes in Taiwan over a period of 10 years. Figure 1 below shows the scientists’ results.

Figure 1
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Using the Hardy–Weinberg equation calculate the frequency of mosquitoes that are heterozygous for the V1016G minus gene in this population in 2014. Show your working.

5b4 marks

Figure 2 shows the change in frequency of the V1016G plus in an area in which the pyrethroid insecticides were being used on a weekly basis. Describe and explain the shape of the curve.

Figure 2

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5c2 marks

Research has shown that the use of pyrethroid insecticides close to waterways has caused the numbers of rainbow trout to decrease. Ecologists studied the frequency of two alleles of a gene in a population of rainbow trout. The dominant allele M, codes for an enzyme. The other allele, m, is recessive and does not produce a functional enzyme.

In a population of rainbow trout, the allele frequency for the dominant allele, M, was found to be 0.6.

Calculate the percentage of homozygous dominant rainbow trout in this population. Show your working.

5d2 marks

After 5 years the ecologists repeated their study of the rainbow trout population. They found that the frequency of the dominant allele had decreased.

A statistical test showed that the difference between the two frequencies of the M allele was significant at the p = 0.05 level. Explain what this means.

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1a2 marks

One of the conditions for the Hardy-Weinberg principle is that no mutations arise. State two others.  

1b3 marks

Rabbits can have either black, grey, or white fur. Scientists crossed a grey rabbit with a black rabbit. The female rabbit produced 12 black rabbits, 7 grey, and 5 white. 

Use this information, and a genetic diagram, to show how these offspring were produced. Use the letter ‘C’ to represent the fur colour gene.

1c4 marks

Another group of scientists wanted to calculate the frequency of the heterozygous grey population of rabbits. The Hardy-Weinberg equations can be adjusted as follows:

 

p2 + 2pq + q2 + 2pr + 2qr + r2 = 1.0

p + q + r = 1.0

 

Where r represents the third allele. They found that the percentage of homozygous black rabbits were 64%, and the frequency of the grey allele was 13%. Use this information and formulae provided to calculate the expected frequency of the heterozygous grey phenotype. 

1d2 marks

The scientists expected the number of offspring phenotypes predicted to differ from the actual numbers obtained. 

Explain why the actual numbers were different from those expected.  

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2a1 mark

In bird species, females are the heteromorphic sex (ZW) and males are homomorphic (ZZ). The genus Meleagris includes the commonly known turkey. Their feathers can be either brown or bronze in colour. Figure 1 shows the inheritance of feather colour in a group of turkeys. 

 Figure 1

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Use Figure 1 to provide evidence that feather colour is sex-linked. 

2b2 marks

Use Figure 1 to explain the evidence that the brown phenotype is recessive. 

2c2 marks

Turkey 4 was found to be heterozygous. It was further crossed with turkey 3 producing more offspring. Use a genetic diagram to predict the likely ratio of phenotypes expected in these offspring.

2d3 marks

The rate of Feather colour production in one species of turkey is controlled by a pair of codominant alleles which are not sex-linked. The allele RF codes for fast feather production while the allele RS codes for slow feather production. Heterozygous chickens produce feathers at a normal rate.

On a farm, 4% of the chickens had fast feather production. Use the Hardy-Weinberg equation to calculate the percentage of this population that you would expect to produce feathers at a normal rate. 

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3a1 mark

State what is meant by the Hardy-Weinberg principle. 

3b2 marks

Rhagoletis pomonella is otherwise known as the apple maggot fly. Initially, these maggots would lay their eggs on hawthorn fruit. In the 19th century a distinct group of maggots emerged that lay their eggs on apples only. Apples and hawthorn fruit are closely related. 

The inheritance of eye colour in the apple maggot flies was investigated. Two flies with red eyes were crossed. Of the offspring, 304 had red eyes and 96 had black eyes.

Using suitable symbols, state and explain the genotypes of the parents. 

3c2 marks

Apple maggot flies can be either white or cream coloured. Scientists studying a population of apple maggot flies found that 43% were cream coloured, which is the recessive phenotype. Use the Hardy-Weinberg equation to calculate the percentage of apple maggot flies that are heterozygous.

3d3 marks

The Hardy-Weinberg equation makes many assumptions about a given population.

Suggest three reasons why the frequency of an allele, or phenotype, calculated using the Hardy-Weinberg equation may be inaccurate. 

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4a3 marks

The Galapagos Islands are a group of small islands 600 miles off the coast of South America. They are the site of Charles Darwin's famous study of finches. The islands are home to many endemic species of animals and plants which means they are not found anywhere else. 

Scientists studying the islands found the prevalence of one species of finch, Geospiza fortis. They discovered a gene, called ALX1, which codes for facial features such as beak shape. This particular species of finch may have blunt or pointed beaks. The scientists found that the blunt beak was better suited for cracking open tough seed coverings. They discovered that the blunt beak was recessive and investigated the frequency of this gene variant within a population. Figure 1 shows the scientists results.

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85% of finches possessed blunt beaks in 2010. Use Figure 1 to calculate the frequency of the heterozygous phenotype in 2010.

4b2 marks

On one island there were 500 finches in the total population. In this population, 300 hadlong beaks with the genotype BLBL, 150 had medium length beaks with the genotype BLBS, with the remainder having BSBS

Use these figures to calculate the actual frequency of the BS allele. 

4c3 marks

Use your answer to part b) and the Hardy-Weinberg equation to calculate the number of finches that would be expected to have the phenotype BLBS.

4d2 marks

Scientists use statistical tests to determine the significance of the data. 

State which statistical test scientists should use for this data. 

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5a2 marks

Malaria is caused by a parasite that attacks red blood cells, producing repeated bouts of serious illness and often causing death. The allele for normal haemoglobin in red cells is HbA. In the West African country of Burkina Faso, 20% of people are heterozygous for a different allele, HbC, which has no effect on their health. People homozygous for HbC suffer a very mild anaemia. Figure 1 shows how the HbC allele affects the chance of getting malaria.

Figure 1

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The HbC allele is increasing in frequency in parts of Africa, such as Burkina Faso. Suggest an explanation for this.

5b2 marks

Scientists investigated the frequency of homozygous HbA individuals in different parts of the world. Table 1 shows their results in Europe and Asia. 

Table 1

Population

Frequency of the HbA HbA Genotype

European

0.97

Asian

0.31

Using Table 1, calculate the frequency of heterozygous genotype in Asia. 

5c3 marks

Figure 2 shows the prevalence of malaria and the frequency of the HbC allele. Those individuals homozygous with HbC HbC develop mild anaemia. Scientists concluded that the HbC allele is more prevalent in areas with higher risk of mortality from malaria. 

Figure 2

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Use the information in Figure 1 to evaluate their conclusion. 

5d2 marks

In a village with a population of 500, there were 8 people who were homozygous for the Normal adult haemoglobin sickle–cell allele and 96 who were heterozygous. 

Calculate the frequency of the HbC allele in the village. 

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