Question

Hemophilia A is caused by an X-linked recessive mutation. A man with hemophilia A is a sickle cell carrier. He has children with a woman who is a carrier of the sickle cell trait; she does not have hemophilia A, but her father did. What is the chance that they have a daughter who carries the hemophilia A mutation and does not carry the sickle cell mutation?

1/8

2/16

4/16

1/4

3/16

1/16

3/8

9/16

Answer 1

Sickle cell anaemia is an autosomal recessive disease so carriers will be heterozygous .Genotype of the man will be X^hYSs and the genotype of the woman he married will be XX^hSs.She is a carrier for hemophilia as she had a hemophilic father whose X chromosome would have borne the trait.

The genotypes of the children would be

	XhS	Xhs	YS	Ys
XhS	XhXhSS	XhXhSs	XhYSS	XhYSs
Xhs	XhXhSs	XhXhss	XhYSs	XhYss
XS	XhXSS	XhXSs	XYSS	XYSs
Xs	XhXSs	XhXss	XYSs	XYss

If the daughter doesn't carry the sickle cell mutation at all then she will have the genotype SS, and if she carries the hemophilia mutation she can be either heterozygous X^hX (carrier) or hemophilic X^hX^h. So the chance is 2\16.