Question

Lesch-nyhan syndrome is an x-linked, rare, recessive disease caused by a mutation in the gene encoding for hypoxanthine-guanine phosphoribosyltransferase (HPRT1). A woman’s maternal grandfather suffered from lesch-nyhan syndrome. She is concerned her male child could have lesch-nyhan syndrome. Genetically, what is the chance that this child has lesch-nyhan syndrome?

a.) 0

b.) 1/8

c.) 1/4

d.) 1/16

e.) 1/2

Answer 1

Ans: option c. (1/4)

Explanation: It is given that disease is rare , so, we will consider that woman's maternal grandmother and husbands of woman and her mother are normal.

Now, Maternal Grand father affected so genotype = xY, Genotype of maternal grand mother = XX

hence, Genotype of woman's Mother = xX ,

Now, Genotype of woman's Father = XY

Genotype of woman = xX or XX

Son will be affected only if x is tranfered from women.

So, probability of transfer of x from women to son = 1/4