Originally Posted by

**deathstarx** Hi there! Hope you all could help me out with the following problems (4 in total):

1. It is known that a certain disease is caused by a gene mutation but is recessive in nature. This means that if B is a normal gene, and b is the disease gene, only people with genotype bb will get the disease. It is also known that in a certain population 2.25% of the population has the disease. Assume that the population is in a Hardy-Weinberg equilibrium. If 2 carriers (Bb gene combi) have children, their children have a 1 in 4 chance of contracting the disease.

Given that a man and his wife do not have the disease, what is the probability that at least one of his first two children will have the disease?

*I chose to do it this way:*

(.25)(.25^2 + (.25x.75x2))

Is this right? My reasoning was that there are 3 types of couples: BB BB, Bb Bb, and BB Bb. So there is a 1 in 4 chance that we have the Bb Bb couple (the others will not have children who have the disease...at most only carriers). Then with regards to the carrier couple, there are 2 scenarios...1 where both children have the disease and the other where only 1 has it.