A prospective groom, who is healthy, has a sister with cystic fibrosis (CF), an autosomal recessive disease. Their parents are normal. The brother plans to marry a woman who has no history of CF in her family. What is the probability that they will produce a CF child? They are both Caucasian, and the overall frequency of CF in the Caucasian population is 1/2500—that is, 1 affected child per 2500. (Assume the population meets the Hardy-Weinberg assumptions.)

Explanation:

From the given information:

Since the parent are normal; Let assume that their trait is Pp

The affected sister  will be recessive in nature, so the trait will be pp

Now, the husband who is the groom will be a carrier with a probability of 2/3 since her sister is affected.

Also, the wife will be carrying a heterozygous trait since she is normal as well.

However, using Hardy-Weinberg assumption:

q = 0.02

Recall that:

Thus,

2pq = 0.0392

Finally, the required probability that there will be an affected offspring amongst the family is:

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.