Polycystic disease (PKD)is an autosomal dominant disease. Symptoms of the disease do not usually present until age 40-50, but it can now be diagnosed earlier using genetic testing.
A woman, whose mother died of PKD, marries a man wo has no history of PKD in his family. The woman is pregnant with their third child. Their first child, a boy, has PKD. Their second child, a daughter, does not. What are the chances that this child will have PKD?
PKD is an autosomal dominant. Hence let us consider the allele that causes PKD to be 'P' and the wild type recessive allele to be 'p'. A cross between the PKD woman who has the genotype Pp as the womans mother died of PKD and their first child is PKD child but second child is normal. The fathers genotype will be pp. Hence a cross between them will result in the following phenotypes:
P | p | |
p |
Pp PKD child |
pp Normal child |
p |
Pp PKD child |
pp Normal child |
Hence the phenotype of PKD child to normal child is 1:1 and hence the probability that the 3rd child will be PKD child is 50%.
If you have any query kindly comment before giving thumbs up. Thank you.
Get Answers For Free
Most questions answered within 1 hours.