Question

assume a phenotype is determined by one gene with a dominant allele and a recessive allele. if one parent is homozygous recessive and the other is heterozygous, what is the probability that an offspring will have the recessive phenotype?
○ 100%
○ 50%
○ 25%
○ 0%
○ 75%

Explanation:

Step1: Define alleles

Let the dominant allele be \(A\) and the recessive allele be \(a\). One parent is homozygous recessive (\(aa\)) and the other is heterozygous (\(Aa\)).

Step2: Set up Punnett square

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

	\(a\)	\(a\)
\(a\)	\(aa\)	\(aa\)

Step3: Calculate probability

Out of 4 possible offspring genotypes (\(Aa,Aa,aa,aa\)), 2 are \(aa\) (recessive phenotype). Probability \(=\frac{2}{4} = 0.5 = 50\%\)

Answer:

B. 50%