Question

sickle - cell anemia is a genetic disease caused by a recessive allele. sickle - cell anemia affects the hemoglobin in red blood cells, making them the shape of crescents instead of discs. the disease can cause pain and damage blood vessels. a genetic counselor meets with a man and a woman that both are carriers of sickle - cell anemia. carriers have one copy of the sickle - cell allele and one copy of the allele for making normal hemoglobin. what is the probability that the couple would have a child that was also a carrier for sickle - cell anemia? 0% 25% 50% 75% 100% done

Explanation:

Step1: Set up Punnett - square

Let the normal allele be $A$ and the sickle - cell allele be $a$. Both parents are carriers with genotype $Aa$.

Step2: Fill in Punnett - square

The possible gametes from each parent are $A$ and $a$. The Punnett - square has 4 possible combinations: $AA$, $Aa$, $aA$, $aa$.

Step3: Determine carrier genotypes

Carriers have the genotype $Aa$. Out of the 4 possible genotypes in the Punnett - square ($AA:Aa:aA:aa = 1:2:1$), 2 out of 4 are carriers ($Aa$ and $aA$ which are equivalent).

Step4: Calculate probability

The probability of having a carrier child is $\frac{2}{4}=0.5$ or 50%.

Answer:

C. 50%