Question

chantal has gauchers disease, a recessive disorder where glucocerebroside builds up to dangerous levels in organs and cells. people with gauchers disease experience bruising, fatigue, anemia and enlargement of the liver and spleen. chantals parents are healthy. they wish to have another child. what is the probability that a second child will also have gauchers disease? multiple choice 1/4 1/3 3/4 2/3

Explanation:

Step1: Determine parents' genotypes

Since Chantal has the recessive disorder and her parents are healthy, both parents must be carriers. Let the normal - allele be $A$ and the disease - causing allele be $a$. So the parents' genotypes are $Aa$.

Step2: Set up Punnett - square

When two carriers ($Aa\times Aa$) have a child, the possible genotypes of their offspring are determined by a Punnett - square. The possible gametes from each parent are $A$ and $a$. The combinations in the Punnett - square are $AA:Aa : Aa:aa=1:2:1$.

Step3: Calculate probability

The genotype for having Gaucher's disease is $aa$. From the Punnett - square, the probability of getting an $aa$ genotype is $\frac{1}{4}$. Each pregnancy is an independent event, so the probability that a second child has the disease is also $\frac{1}{4}$.

Answer:

A. $\frac{1}{4}$