gcseprep.com · web viewa mutation of this gene forms a recessive allele which, when translated,...

Topic 8 – Origins of Genetic Variation

Q1.

Poliomyelitis is a serious disease that can lead to muscle weakness, paralysis and death. There is no cure.

Poliomyelitis is caused by poliovirus.

The first poliovirus vaccine was tested in a study using 1.8 million children.

These children were divided into three groups.

Children in group 1 were treated with the vaccine.

(i) Devise suitable treatments for the children in group 2 and group 3.

(2).............................................................................................................................................

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(ii) There are three types of poliovirus: PV1, PV2 and PV3. Each type causes poliomyelitis.

The table shows the results of the study for each type of poliovirus for children in group 1.

A few children had a severe allergic reaction to the vaccine.Comment on the extent to which this study supports the widespread use of this vaccine.

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Q2.

The retina is the light sensitive structure in the eye.

Red-green colour vision is controlled by a single gene located on the X chromosome.

Colour blindness is caused by a recessive allele for the red-green colour vision gene.

The diagram shows the inheritance pattern of colour blindness for a family.

(i) Explain how the diagram shows that red-green colour blindness is caused by a recessive allele.

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(ii) Use a genetic diagram to determine the probability that the next child of individuals 6 and 7 is a male who is colour blind.

(3)

Answer ...........................................................

(Total for question = 5 marks)

Q3.

Tomato plants and potato plants are both affected by a fungal disease called blight.

In 2014, a study was carried out to compare the yield of potatoes genetically modified (GM) for blight resistance with the yield of non-modified (non-GM) potatoes.

The study was carried out using 96 plants of each variety, equally divided between six different plots.

The graph shows the results of this study.

(i) Calculate the percentage change in yield due to blight resistance in plot 2.

(2)

Answer ........................................................... %

(ii) The raw data for potato yield in this study are shown in the table.

A Student's t-test was used to compare the potato yields.

State a suitable null hypothesis for this test.

(1).............................................................................................................................................

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(iii) Calculate the t value for the data to compare GM with non-GM potato yields, using the formula:

(3)

Answer ...........................................................

(iv) The table shows the critical values of t with 10 degrees of freedom.

Use your value of t to test the validity of the null hypothesis.(3)

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Q4.

The ability to taste phenylthiocarbamide (PTC) depends on a single gene.

This gene has two alleles. One is a dominant, tasting allele (T), and the other is a recessive, non-tasting allele (t).

In a survey, it was found that 64% of people could taste PTC.

(a) The Hardy-Weinberg equation is

(p + q)2 = 1

Use this equation to calculate the proportion of the population who would be TT, Tt and tt.

(4)

(b) There is no known selective advantage for being able to taste PTC.

(i) Describe two conditions under which these proportions remain the same over many generations.(2)

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(ii) In native American populations 98% of individuals can taste PTC.In native Australian population 58% of individuals can taste PTC.State why these two populations have different frequencies of the T allele.

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Q5.

The diagram shows four varieties of rabbit.

Fur colour in rabbits is controlled by four different alleles:

· the allele for brown fur, C, is dominant to all other alleles· the allele for chinchilla fur, cch, is dominant to the alleles for Himalayan and albino· the allele for Himalayan fur, ch, is dominant to the allele for albino· the allele for albino fur, c, is recessive to all other alleles

(i) Describe how new combinations of alleles are produced in meiosis.

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(ii) State all the possible genotypes of a rabbit with brown fur.

(1) .............................................................................................................................................

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(iii) Two parent rabbits with brown fur were mated. Two of the F1 offspring had chinchilla fur.

The F1 rabbit offspring with chinchilla fur were mated.The F2 generation consisted of some rabbits with chinchilla fur and the rest having Himalayan fur.Use genetic crosses to deduce the genotypes of the two parent rabbits with brown fur.

(3)

Answer ...........................................................


Q6.

A defect in the cone cells of the retina can result in colour blindness.

(a) Which is the visual pigment found in cone cells?

(1)

A iodopsin

B opsin

C retinol

D rhodopsin

(b) The table below shows the distribution of different cones involved in colour blindness.

(i) The population of London is 12 million, of which 55% are men.Calculate the number of men in London who are colour blind.

(3)

Answer ...........................................................

(ii) The allele for one defect in cone cells is recessive and carried on the X chromosome.Explain why more men than women are colour blind.

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(iii) L-cones respond to long wavelengths of light.M-cones respond to medium wavelengths of light.S-cones respond to short wavelengths of light.The visible light spectrum is shown below.

Analyse the data to explain why red/green colour blindness is the most common throughout the population.

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Q7.

The diagram shows four varieties of rabbit.

Fur colour in rabbits is controlled by four different alleles:

· the allele for brown fur, C, is dominant to all other alleles· the allele for chinchilla fur, cch, is dominant to the alleles for Himalayan and albino· the allele for Himalayan fur, ch, is dominant to the allele for albino· the allele for albino fur, c, is recessive to all other alleles

The fur colour of animals can be affected by natural selection.

Compare and contrast stabilising selection with disruptive selection.

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Q8.

In the fruit fly, Drosophila, the allele for normal wings (N) is dominant to the allele for vestigial (small) wings (n).

The allele for red eyes (R) is dominant to the allele for sepia eyes (r).

In an investigation, students crossed homozygous parent flies. Flies with normal wings and red eyes were crossed with flies with vestigial wings and sepia eyes.

All the F1 offspring of this cross had normal wings and red eyes.

Flies from this F1 generation were crossed and the phenotypes of their offspring (F2 generation) were counted.

The results for the F2 generation are shown in the table.

The students thought that the genes for wing length and eye colour were on different chromosomes.

* In Drosophila, the allele for grey bodies (G) is dominant to the allele for black bodies (g).

In a second investigation, students crossed homozygous parent flies. Flies with normal wings and grey bodies were crossed with flies with vestigial wings and black bodies.

All the F1 offspring had normal wings and grey bodies.


The results are shown in the table.

Explain the results of this second investigation.

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Q9.

Sickle cell anaemia is caused by a mutation in the β-globin gene which codes for part of haemoglobin.

The diagram shows the first 10 amino acids in this part of haemoglobin, in a healthy person and in a person with sickle cell anaemia.

The allele that leads to sickle cell anaemia is known as HbS.

From 1990 to 1996, all newborn infants in California were screened for the presence of the HbS allele.

The data in the table show the ratio of individuals with and without the HbS allele, in various ethnic groups.

A chi squared test was used to analyse the raw data.

The null hypothesis was: "There is no difference between the frequency of the HbS allele in African Americans and in all other ethnic groups combined."

The calculated value of chi squared was 450 615.

The table shows some critical values for the chi squared distribution, with one degree of freedom.

Malaria is a major cause of death in Africa.

Assess the effect that this might have on the frequency of the HbS allele in African populations.

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Q10.

The stems of tomato plants can be green or purple, hairy or smooth.

The allele for purple stems (P) is dominant to the allele for green stems (p). The allele for hairy stems (H) is dominant to the allele for smooth stems (h).

Two tomato plants, heterozygous for both stem characteristics, were crossed.

Draw a genetic diagram to show the expected ratio of phenotypes of the plants obtained from this cross.

(4)

Q11.

There are many disorders that affect the health of people.

The graph shows the number of people in the world who die each year from different health disorders.

* Some health disorders, such as sickle cell anaemia, have a genetic basis.

People who are at risk of these disorders can be identified using genetic tests.

Hospital managers need to predict the future cost of treating people with health disorders.

It has been claimed that the Hardy-Weinberg equation (p + q = 1 or p2 + 2pq + q2 = 1) could be used to predict the number of people who would need treatment for health disorders.

Discuss the validity of this claim.

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Q12.

Cystic fibrosis is a recessive inherited condition where the cells in the lungs produce sticky mucus. This mucus builds up in the airways, causing breathlessness and chest infections.

People with cystic fibrosis often need treatments such as physiotherapy and antibiotics.

The incidence of babies born with cystic fibrosis in Australia is 1 in 2500.

Use the Hardy Weinberg equation, p2 + 2pq + q2 = 1, to calculate the percentage of Australians who are carriers of cystic fibrosis.

(4)

Answer ........................................................... %


Q13.

In the fruit fly, Drosophila, the allele for normal wings (N) is dominant to the allele for vestigial (small) wings (n).

The allele for red eyes (R) is dominant to the allele for sepia eyes (r).

In an investigation, students crossed homozygous parent flies. Flies with normal wings and red eyes were crossed with flies with vestigial wings and sepia eyes.

All the F1 offspring of this cross had normal wings and red eyes.


The results for the F2 generation are shown in the table.

The students thought that the genes for wing length and eye colour were on different chromosomes.

(i) State a null hypothesis for this investigation.

(1) .............................................................................................................................................

(ii) A Chi squared test was carried out to test this hypothesis.

Complete the table.(1)

(iii) Calculate the value of Chi squared using the formula

(1)

Answer ...........................................................

(iv) The table shows some critical values of Chi squared at different degrees of freedom.

Use this table to comment on the results of the investigation.(3)

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Q14.

'DELLA' proteins normally prevent transcription factors from binding to important growth-stimulating genes in the cells of plant stems.

The diagram below shows part of the biochemical pathway leading to the synthesis of an active plant growth substance called gibberellin (GA1). GA1 reduces the effect of 'DELLA' proteins.

(a) The Le-1 gene codes for the enzyme GA20 oxidase. A mutation of this gene forms a recessive allele which, when translated, leads to a single amino acid change in this enzyme. This change significantly reduces the activity of GA20 oxidase.

Explain how a single amino acid change can bring about a change in the structure and activity of GA20 oxidase.

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(b) (i) Explain why homozygous recessive plants will have short stems.

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(ii) An ecological survey of a stable population of one species of plant found that 36% had short stems.

Calculate the percentage of heterozygous individuals in this population. Assume that there are only two alleles for this gene.

(4)

Answer ...........................................................


Q15.

Cystic fibrosis is a recessive inherited condition where the cells in the lungs produce sticky mucus. This mucus builds up in the airways, causing breathlessness and chest infections.

People with cystic fibrosis often need treatments such as physiotherapy and antibiotics.

A woman is a carrier of the cystic fibrosis allele. Her partner does not have cystic fibrosis and is not a carrier.

Use a genetic cross to determine the probability of this woman producing a child who is also a carrier.

(4)

Probability ...........................................................


Q16.

Sickle cell anaemia is caused by a mutation in the β-globin gene which codes for part of haemoglobin.

The diagram shows the first 10 amino acids in this part of haemoglobin, in a healthy person and in a person with sickle cell anaemia.

The allele that leads to sickle cell anaemia is known as HbS.

From 1990 to 1996, all newborn infants in California were screened for the presence of the HbS allele.

The data in the table show the ratio of individuals with and without the HbS allele, in various ethnic groups.

A chi squared test was used to analyse the raw data.

The null hypothesis was: "There is no difference between the frequency of the HbS allele in African Americans and in all other ethnic groups combined."

The calculated value of chi squared was 450 615.

The table shows some critical values for the chi squared distribution, with one degree of freedom.

Explain the conclusion that can be drawn from this chi squared test.

(3).............................................................................................................................................

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Q17.

The graph shows the frequency of a characteristic found in a population of animals.

Which type of selection would create this pattern?

(1) A allopatric selection B directional selection C disruptive selection D stabilising selection

(Total for question = 1 mark)

gcseprep.com · web viewa mutation of this gene forms a recessive allele which, when translated,...

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