Populations (A Level only) (AQA A Level Biology): Exam Questions

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 B^R.

Chickens have three possible genotypes:

B^RB^R resistant to brodifacoum

B^RB^V resistant to brodifacoum

B^VB^V susceptible (not resistant) to brodifacoum

Chickens, with the genotype B^RB^R, 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 B^RB^R, 118 had the genotype B^RB^V  and 6 chickens had the genotype B^VB^V.

Calculate the actual frequency of the allele B^R in this population. Show your working.

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. 

Out of the population of 160, calculate the number of chickens that would be likely to die within a few days.

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

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

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

Use a genetic diagram to show how this could occur.

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 (C^P) is dominant over the yellow allele (C^Y).

Define the term population. 

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. 

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

State what can be concluded from this.

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.

In a species of goat coat colour is controlled by one gene. Coat colour may be brown, black or white. The allele for brown, C^B, is dominant to the other two alleles. The allele for black, C^A, is dominant to the allele for white, C^W.

Define the term recessive in the context of alleles.

A cross between two brown-coated goats produced only brown-coated and black-coated goats. Draw a genetic diagram to explain this outcome.

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

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.

In Borneo the blood type of 300 orangutans were sampled by ecologists. In the orangutan population 81 orangutans had the genotype I^AI^O, 63 had the genotype I^BI^O, 153 had the genotype I^AI^B and 3 had the genotype I^OI^O. 

With reference to the given information, define the term gene pool.

State what is predicted by the Hardy-Weinberg principle.

Calculate the frequency of the allele I^O in the orangutan population. 

Note that the Hardy-Weinberg equation should not be used in your calculation.

In a population of 500 orangutans the frequency of the I^O allele was 0.3. 

State what the Hardy-Weinberg principle will predict about the frequency of the I^O allele after another 5 generations.

Pyrethroids are sprayed insecticides used to kill mosquitoes. These insecticides are used in parts of Asia to control the spread of dengue, a virus that is transmitted by Aedes aegypti mosquitoes. 

The A. aegypti mosquito has 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

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.

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.

Figure 2

Describe and explain the shape of the curve.

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.

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.

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

State two other conditions.  

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 to draw a genetic diagram that shows how these offspring were produced. Use the letter C to represent the fur colour gene.

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. 

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.  

In birds females are heteromorphic (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

Use Figure 1 to justify the statement that 'feather colour is sex-linked'. 

Use Figure 1 to justify the statement that 'brown phenotype is recessive'. 

Turkey 4 was found to be heterozygous. It was further crossed with turkey 3 producing more offspring.

Draw a genetic diagram to predict the likely ratio of phenotypes expected in these offspring.

The rate of feather production in one species of turkey is controlled by a pair of codominant alleles which are not sex-linked. The allele R^F codes for fast feather production while the allele R^S 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. 

State what can be estimated using the Hardy-Weinberg principle. 

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

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

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

Apple maggot flies can be either white or cream coloured. Scientists studying a population of apple maggot flies found that 43 % were cream coloured; this is the recessive phenotype.

Use the Hardy-Weinberg equation to calculate the percentage of apple maggot flies that are heterozygous.

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

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

Scientists studying a species of Galapagos finch, Geospiza fortis, discovered a gene, ALX1, which codes for beak shape. This particular species of finch may have blunt or pointed beaks.

The scientists discovered that the allele for blunt beaks was recessive and they investigated the frequency of this allele within a population. Figure 1 shows their results.

Figure 1

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

On an island in the Galapagos there were 500 finches in a population. In this population, 300 had long beaks with the genotype B^LB^L, 150 had medium length beaks with the genotype B^LB^S, with the remainder having short beaks, B^SB^S. 

Use these figures to calculate the frequency of the B^S allele. 

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 B^LB^S.

Susceptibility to the disease malaria varies according to an individual's haemoglobin genotype. The allele for normal haemoglobin is Hb^A. In the West African country of Burkina Faso, 20 % of people are heterozygous for the haemoglobin gene and have the genotype Hb^AHb^C. People with the genotype Hb^CHb^C suffer a very mild form of anaemia.

Figure 1 shows how the Hb^C allele affects the chance of getting malaria.

Figure 1

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

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

Table 1

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

Figure 2 shows the prevalence of malaria and the frequency of the Hb^C allele. Individuals with the genotype Hb^CHb^C develop mild anaemia. Scientists hypothesised that the Hb^C allele is more prevalent in areas with higher risk of mortality from malaria. 

Figure 2

Use the information in Figure 1 to evaluate their hypothesis. 

In a village with a population of 500, there were 8 people who were homozygous for the normal adult haemoglobin allele and 96 who were heterozygous at this gene locus. 

Calculate the frequency of the Hb^C allele in the village.