Exam 9: Inheritance

Haemophilia is a defect in blood clotting. It is a recessive trait that has arisen from a mutation of a gene on the X-chromosome. A boy with haemophilia has parents who have normal blood clotting. If the parents have another child what is the probability it will be normal?

In tomato plants, a gene controlling fruit shape has 2 alleles: O (round) and o (oval). A gene controlling inflorescence (position of the flowers) has two alleles: S (simple) and s (compound). A pure-breeding plant with oval fruit and simple inflorescence is crossed to a pure-breeding plant with round fruit and compound inflorescence. All the offspring have round fruit and simple inflorescence. The offspring are then crossed to plants with oval fruit and compound inflorescence. The phenotypes of this second generation are Oval simple 200 Round compound 190 Oval compound 50 Round simple 60. Which statement about the genes is true?

Red-green colour-blindness in humans is a recessive X-linked trait. A man and a woman with normal vision have a colour-blind son. What is the probability that their next child will also be a colour-blind son?

In a flowering plant, a mutation in a gene controlling flower structure results in flowers with extra petals. A mutation in another gene results in no flowers (flowerless). Both mutant phenotypes are recessive, and the two genes assort independently. If a plant heterozygous for both mutations self-fertilises, which of the following ratios would you expect in the offspring?

Which of the following is a description of codominance?