Question

Consider the following pedigree of a rare X-linked recessive disease. a) If individuals A and B have a child, what is the probability that the child will have the disease? b) If individuals C and D have a child, what is the probability that the child will have the disease? c) If the first child of C and D is normal, what is the probability that their second child will have the disease? d) If the first child of C and D has the disease, what is the probability that their second child will have the disease?

Answer 1

a) Male gamets X^c Y Female gamets X^c X Disease is X - linked recessive, therefore, 50% chance of having diseased child 25% chance of a carrier female child b) rightarrow D can be XX(normal) or X^c X rightarrow she is normal, then all carrier of her child are normal rightarrow But, if she is a carrier of diseases gene then probability will be All normal rightarrow 50% male child diseased rightarrow 50 % female child may be carrier of diseases but not diseased female child rightarrow in probability, 25% or 1/4, child have the chance of disease c) If the first child of C and D is normal, The probability of second child have disease 1/4 or 25% d) If the first child of C and D has disease, then also the probability of second child have disease is 1/4 or 25%