Question

A married couple discovers that there was a case of the X-linked recessive disorder Duchenne Muscular Dystrophy (DMD) in the grandparental generation on both sides of their family. the prdigree is as follows:

i) should the DMD case on the man's side affect the anxiety level of the couple at all? Explain.

ii)What is the probanility that their first child will be a boy with DMD?

8. A married couple discovers that there was a case of the X-linked recessive disorder Duchenne Muscular Dystrophy (DMD) in the grandparental generation on both sides of their family. The pedigree is as follows i) Should the DMD case on the man's side affect the anxiety level of the couple at all? Explain. what is the probability that their first child will be a boy with DMD? ii)

Answer 1

i) The man with the family history of muscular dystrophy is normal. The genotype of males is XY, if he carried a mutant allele for muscular dystrophy it would manifest as disease because males have only one X chromosome. Affected males start showing signs of the disease by the age of 4.The man in this case is at a reproductive age and normal, therefore there is no chance that he is carrying dystrophy causing X^d allele. The genotype of this man is normal XY. Therefore DMD case on man's side should not affect the anxiety level of the couple.

ii) The married couple's child can have muscular dystrophy only when the mother is a carrier because father is already known to be unaffected XY.

First we have to find the probability that the mother is a carrier.

So starting from the grand parental generation First we will calculate the probability that her grandmother is a carrier, then the probability if her mother is a carrier, then the probability that she is the carrier. Next we calculate the probability that the married couple has an affected son if mother is carrier

The probability of all these individual independent eventsoccuring together is the product of individual probabilities. We are not taking grandfather and father into consideration as they are normal and do not carry the disease causing allele.