In humans, Pseudohypertrophic Muscular Dystrophy is a condition in which the nerves waste away during early life, resulting in death by the early teens. This lethal disease is due to a recessive sex-linked gene. A couple has five children - three boys, and two girls. The oldest boy has the disease. You are their family geneticist and they come to you for advice. What could you tell them about the chances of their other two boys and their two girls also having this disease? (HINT: You must determine the parent genotypes and then show a Punnett square. Use that as your source for advice giving.) • parents = • 10 year old boy = %3D • female children male children

In humans females possess two X chromosomes and males possess one X chromosome and one Y chromosome.

Given it is a sex linked recessive disorder.It should be X-linked disorder. It is not Y-linked .If it is Y-linked,then male parent might be affected and won't exist at all ,since this is a lethal disorder. Also, X chromosome of the male parent is not affected,it is a normal one.

Therefore genotype of male parent is XY.

It's affect is seen only in the absence of dominant allele. One affected X chromosome is enough to have it's effect in males because males have only one copy of X chromosomes. Two X chromosomes need to be affected to see it's effect in female individuals.