Question

1. the pedigree below tracks the presence of attached earlobes through a familys generation.

having attached earlobes is an autosomal recessive trait.

what is the probability that offspring x will have unattached earlobes?

a. 0%
b. 25%
c. 50%
d. 75%

Explanation:

Step1: Determine the genotypes

Since attached earlobes is an autosomal - recessive trait (let the recessive allele be \(a\) and the dominant allele be \(A\)). Individuals with attached earlobes have genotype \(aa\).
Individual \(III - 5\) has attached earlobes (\(aa\)). Individual \(III - 6\) has unattached earlobes. But to have a child with the possibility of attached or unattached earlobes, individual \(III - 6\) must be a carrier (\(Aa\)) because if \(III - 6\) was \(AA\), all offspring would have unattached earlobes.

Step2: Use Punnett square

The cross is \(aa\times Aa\). The possible gametes from \(aa\) is \(a\), and from \(Aa\) are \(A\) and \(a\).
The Punnett square is:

	\(A\)	\(a\)

The probability of \(Aa\) (unattached earlobes) is \(\frac{1}{2}\), and the probability of \(aa\) (attached earlobes) is \(\frac{1}{2}\)

Answer:

C. 50%