Question

The pedigree above shows the inheritance history of a trait that is known to be due to a sex- linked allele. a) is the allele responsible for the trait recessive or dominant? Explain your reasoning. (2 marks b) What is the chance that the fifth (5) child born to III-11 and 111-12 will be affected? (1 mark) c) What is the chance that the sixth (6) child born to III-11 and III-12 will be a female carrier? (1 mark) Display Settings Focus -- here to search O

Answer 1

Ans. a

Allele is X-linked recessive for trait because the two normal parents i.e. 1 and 2 or 4 and 5 are having affacted offspring which is only possible when Male is healthy and female is carrier.

Ans. b

III - 12 will be carrier because their son (IV-6) is affacted which is only possible when mother having mutant allele.

Now 5th child may be male or female but the it will decided by the X gene from mother that child is affacted or not. 1/2 chances will there to be affacted child.

Ans. c

6th child to be born girl child will be 1/4

1/2 chances to be girl child and further 1/2 chances will there that gamete with X chromosome having normal gene will fuse with fathers X chromosome bearing gamete.