In 1995, doctors reported a Chinese family in which retinitis pigmentosa (progressive degeneration of the retina leading to blindness) affected only males. All six sons of affected males were affected, but all of the five daughters of affected males (and all of the children of these daughters) were unaffected. a. What is the likelihood that this form of retinitis pigmentosa is due to an autosomal mutation showing complete dominance? b. What other possibilities could explain the inheritance of retinitis pigmentosa in this family? Which of these possibilities do you think is most likely?

In Y linked diseases, it has parental transmission from the fathers to the sons, since they have XY in the 23rd pair. So, they never transmit the Y chromosome to the daughters (XX), and they will not transmit it to their offspring. I think this is the most likely answer.

In the case of recessive X linked traits, woman have two copies of the X chromosome, so even if they have a mutation in one of the alleles, they will not develop the disease, since they have a normal copy of the gene (they become healthy carriers). Males only have one X chromosome, so they don´t have the possibility of harboring a normal allele and they will develop the disease.