With the help of the given pedigree, find out the probability for the birth of a child having no disease and being a carrier (has the disease mutation in one allele of the gene) in the F3 generation.
Show Hint
Draw a Punnett square for the F2 parents (Aa x aa) to visualize the probabilities of the F3 offspring's genotypes.
The affected male (shaded square) has the genotype aa because the disease is autosomal recessive. An individual with the "aa" genotype will show the disease, as two copies of the recessive allele are needed to express the trait.
The female is a carrier, so her genotype must be Aa, meaning she carries one allele for the disease (a) but has one normal allele (A), making her asymptomatic but capable of passing the "a" allele to her children.
Step 2: Genotypes of F3 Generation (Offspring)
Let's consider the possible genotypes of their children (F3 generation). We can use a Punnett square to predict the potential outcomes of the offspring's genotypes.
Punnett Square:
The father with genotype aa can only pass on the a allele to his children, while the mother with genotype Aa can pass on either the A or the a allele. The following genotypes are possible for their children:
Aa (carrier, no disease) — if the child inherits the A allele from the mother and the a allele from the father.
aa (affected, has the disease) — if the child inherits the a allele from both parents.
Therefore, the probability of an offspring being a carrier (Aa) is 1/2, and the probability of an offspring being affected (aa) is also 1/2.
Step 3: Probability of a Carrier in F3
The question asks for the probability that a child from this couple (F3 generation) will be a carrier (Aa).
From the analysis above, we can see that the offspring have a 50% chance of being a carrier (Aa), which means the probability of a child being a carrier is 1/2.
Step 4: If the Question Asks About Gender-Specific Probabilities
If the question specifically asks about the probability of having a daughter who is a carrier, the probability remains the same at 1/2 for that particular child. The gender of the child does not affect the autosomal inheritance pattern in this case because the trait is autosomal (not linked to sex chromosomes).
However, if the question asked for a more specific scenario, such as the probability of a daughter being a carrier and eventually becoming affected (with multiple conditions), the calculation might change, but the basic principle would remain the same.
Final Answer
The probability of any child being a carrier (Aa) is 1/2.
If the question asks specifically about a daughter, the probability of her being a carrier is still 1/2 for that child.
