17 Inherited change Exam-style questions. AQA Biology

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1 1 Two genes in a mouse interact to control three possible coat colours: grey, black and brown. The two genes are located on separate chromosomes. Each gene has two alleles: A is dominant to a and B is dominant to b. a Define the terms. i Gene ii Allele The table below shows four genotypes and phenotypes of mice. Genotype AABb Aabb aabb aabb Phenotype grey grey black brown b Give the phenotype you would expect from each of the following genotypes: i AABB, ii AaBb, iii AAbb, iv aabb c An AABB male was crossed with an aabb female. i Give the genotype of their offspring (F 1 ). ii A female from the F 1 offspring was crossed with a brown male. Give the ratio of phenotypes for this cross. This resource sheet may have been changed from the original 1

2 2 The diagram shows the inheritance of cystic fibrosis in one family. a Cystic fibrosis is caused by a recessive allele. Explain the evidence for this given in the diagram. b Couple 7 and 8 decide to have another child. What is the probability that this child will be a girl with cystic fibrosis? Complete the genetic diagram to explain your answer. Use the symbols N for the dominant allele and n for the recessive allele. 7 8 Parental phenotypes Unaffected Unaffected Parental genotypes Genotypes of gametes Offspring genotypes Offspring phenotypes Probability of girl with cystic fibrosis (4 marks) AQA Biology, 2010, Unit 4 (Question 6) This resource sheet may have been changed from the original 2

3 3 Coat colour in cats is controlled by two codominant alleles, O which gives an orange coat and B which gives a black coat. These alleles are sex linked. Heterozygous individuals have a coat that is a mixture of orange and black. This is known as tortoiseshell. a The gene for coat colour in cats is only found on the X chromosome. Explain why. b i Give the genotypes of the following cats: black female orange male ii A breeder decided to breed these two cats to get tortoiseshell kittens. The resulting litter had two black kittens and one tortoiseshell kitten. There were no orange kittens. Explain why. 4 Human ABO blood groups are determined by the presence or absence of two antigens (A and B) on the plasma membrane of the red blood cells. The inheritance of these blood groups is controlled by three alleles. I A determines the production of antigen A I B determines the production of antigen B I o determines the production of no antigen Alleles I A and I B are codominant. Allele I o is recessive to both. This resource sheet may have been changed from the original 3

4 The pedigree shows the pattern of inheritance of these blood groups in a family over three generations. a i How many antigen-determining alleles will be present in a white blood cell? Give a reason for your answer. ii Which antigen or antigens will be present on the plasma membranes of red blood cells of individual 5? b If individuals 6 and 7 were to have another child, what is the probability that this child would be male and blood group A? Explain your answer. (3 marks) AQA Biology, 2005, Unit 5 (Question 4) 5 One variety of domestic chicken has either black feathers or barred feathers. This is controlled by a gene on the X chromosome. The recessive allele, b, leads to feathers that are black. The dominant allele, B, leads to barred feathers, that are black with white bars. a A breeder crossed a black female with a barred male. Twelve offspring were produced: 3 barred males, 2 barred females, 4 black males, 3 black females. Complete the genetic diagram to explain this. Use the following symbols This resource sheet may have been changed from the original 4

5 X B an X chromosome with the allele for barred feathers X b an X chromosome with the allele for black feathers Y a Y chromosome In birds, it is the female, XY, which is the heterogametic sex. The male, XX, is homogametic. Parental phenotypes Black female Barred male Parental genotypes Gamete genotypes Offspring genotypes Offspring phenotypes (4 marks) b It is quite difficult to tell the sex of newly hatched chicks. The breeder wished to have an easy method by which he could tell the sex of the chicks. Draw a genetic diagram to explain what colours of adult birds should be crossed to enable him to do this. (3 marks) AQA Biology, 2007, Unit 5 (Question 5) 6 In guinea pigs, hair length and hair colour are controlled by two genes on different chromosomes. The hair may be either long or short and its colour either black or brown. a A male guinea pig and a female guinea pig both had short, black hair. The male was homozygous for hair length, and the female was homozygous for hair colour. Repeated crossings of these two guinea pigs resulted in offspring of four different genotypes, all of which had short, black hair. Complete the genetic diagram to explain these results. Write in the box the symbols you will use to represent the alleles. This resource sheet may have been changed from the original 5

6 Allele for short hair Allele for black hair Allele for long hair Allele for brown hair Male Female Parental phenotypes Short, black hair Short, black hair Parental genotypes Gamete genotypes Offspring genotypes Offspring phenotypes Short, black hair (4 marks) b In another investigation, the same female guinea pig was twice mated with another male which had long, brown hair. Of the 14 offspring, 10 had short, black hair and 4 had long, black hair. The investigators expected equal numbers of offspring with these two phenotypes. They used a χ 2 test to determine whether the observed results fitted the expected 1:1 ratio. i Give a suitable hypothesis for the investigation. ii Complete Table 1 to calculate the value of χ for the results. Phenotype Observed (O) Expected (E) (O E) (O E) 2 ( O E) E 2 Short, black hair 10 Long, black hair 4 2 χ (O E) E 2 Table 1 This resource sheet may have been changed from the original 6

7 iii Use Table 2 to determine whether the null hypothesis is supported by the data. Explain how you arrived at your answer. Degrees of freedom Table 2 Probability value (3 marks) AQA Biology, 2007, Unit 5 (Question 8) This resource sheet may have been changed from the original 7