Question

9. Zoe is heterozygous for both an X-linked mutation that causes hemophilia and for a lethal X-linked mutation in a gene whose product is essential in every cell (every cell expressing this mutation will die). These two deleterious mutations are located on the same X (the other X is wild type for these genes). a. Do you expect Zoe to have more sons or more daughters (on average)? Why? b. Zoe has two children (a son and a daughter). Do you expect either of them to have hemophilia? Why or why not? 10. Androgen Insensitivity Syndrome results from a recessive mutation in the X-linked gene that encodes the receptor for testosterone. The cells of XY individuals carrying this mutation are essentially "testosterone blind". If a woman heterozygous for this mutation has children with a normal man, what fraction of her children will be phenotypically female? Of those, what fraction will be fertile?

Please make sure to explain thoroughly. I need to master concepts. Thumbs up will be given!

Answer 1

1) females are XX and males are XY, males inherit the X chromosome from the mother.

Zoe has a lethal mutation in one of her X chromosomes, so all those sons who inherit the x chromosome with the lethal mutation are not viable ( all-male embryos developing from the egg will express the lethal gene, so is not viable, since there is only one X chromosome with mutation).

girls inherit X chromosome from both father and mother, the father could survive up to reproduction means he does not carry the lethal allele, so the daughters can be either homozygous for the normal allele or heterozygous for the lethal mutation, so all the daughters will survive.

so Zoe is likely to have more daughters than sons.

b) the lethal allele is located on the X chromosome with the mutant allele for hemophilia, the sons of Zoe does not inherit the lethal allele, if the recombination has occurred between the X chromosomes, it is possible for the son to get X chromosome with allele for hemophilia and the normal allele for the other gene., those sons will be hemophilic.

nothing is said about the phenotype of her husband let`s assume he is normal, then the daughter cannot be hemophilic, because they will get normal allele from father via X chromosome.

Son can be Hemophilic if recombination occurs between the X chromosomes.

2) her husband has to be normal.

let the alleles be XA- normal allele, Xa- recessive allele results in androgen insensitivity.

XAXa * XAY

	XA	Xa
XA	XAXA ( normal female)	XAXa ( normal female)
Y	XAY ( normal male)	XaY ( phenotypically female, genotypically male)

the proportion of phenotypically females= number of phenotypical females/total number=3/4

the proportion of sterile phenotypically female progenies= number of sterile female/number of phenotypically female

= 1/3