Question

You are studying YFD (your favorite disease). While looking at a pedigree you notice that one of five children have symptoms of YFD, yet neither parent has the disease. What can you conclude about YFD?

1) The trait is X-linked
2) The trait is autosomal dominant
3) The trait is autosomal recessive
4) We do not have enough data to conclude anything

Answer 1

YFD is likely an autosomal recessive trait since only one child out of five is affected and neither parent shows symptoms of the disease, suggesting both parents are carriers of a recessive allele. Option 3.

Step-by-step explanation:

Given the pedigree where only one of five children shows symptoms of Your Favorite Disease (YFD) and neither parent has the disease, we can deduce that YFD is likely an autosomal recessive trait. For a recessive trait to be expressed, an individual must inherit two copies of the recessive allele, one from each parent.

If the trait was autosomal dominant, we would expect to see the disease in one of the parents, since only one copy of a dominant allele is needed for the trait to be expressed.

Regarding X-linked inheritance, if the trait were X-linked and recessive, we would expect to see a difference in the distribution between males and females affected, with males being more likely to be affected.

This is because males have only one X chromosome; thus, a single recessive allele on the X chromosome would result in the trait's expression. However, since the disease is not showing a sex bias and none of the parents show the trait, this reduces the likelihood of it being X-linked.

So Option 3 is correct.