Question

Question 3 5 marks The following pedigree shows a family affected by a rare late-onset disease which is due to a mutation in a maternally imprinted gene. Individuals in generations I and II are all old enough to display the phenotype and all affected individuals are shown. Since this is a late onset disease, individuals in generation III are not yet old enough to display the phenotype, and therefore there are no affected individuals marked in this generation yet. The genotype for each individual in the pedigree is shown. B, wild type allele; b, mutated allele. BB Bb I II BB вь BB Bb BB 2 і вь Bb вь BB Bb a) 12 is affected and has 3 children, all of whom are unaffected. For every child (112, 113, 114), explain why they are unaffected. (3 marks) b) When the individuals in generation III are old enough to show a phenotype, which of these 5 children would you expect to be affected? Why? (2 marks)

Answer 1

Here we have to consider two things ie. Maternally & imprinted. Maternally imprinted genes are paternally expressed.

A) In generation ll

2, and 4 are not affected becuase they are receiving the imprinted b gene from mother. The imprinted gene will not be expressed. 3 is not receiving b from mother, it has B wild gene from mother.

B) In generation lll

1 and 2 will be affected because they have received b from father which is not imprinted (paternally expressed). Where as 3, 4 and 5 will not be affected becuase they receive b from mother and it will be imprinted.(not expressed).