Question

question 7
which of these crosses will produce only heterozygous offspring?
aa x aa
aa x aa
aa x aa
aa x aa

Explanation:

Step1: Analyze \(AA\times Aa\)

Parents: \(AA\) (gametes \(A\)) and \(Aa\) (gametes \(A\) and \(a\)). Offspring genotypes: \(AA\) (\(A\times A\)) and \(Aa\) (\(A\times a\)). So, not all heterozygous.

Step2: Analyze \(Aa\times Aa\)

Parents: \(Aa\) (gametes \(A\) and \(a\)). Using Punnett square: \(AA\) (\(A\times A\)), \(Aa\) (\(A\times a\)), \(aA\) (\(a\times A\)), \(aa\) (\(a\times a\)). Genotypes: \(AA:Aa:aa = 1:2:1\). Not all heterozygous.

Step3: Analyze \(AA\times aa\)

Parents: \(AA\) (gametes \(A\)) and \(aa\) (gametes \(a\)). Offspring: \(Aa\) (\(A\times a\)) only. All heterozygous.

Step4: Analyze \(Aa\times aa\)

Parents: \(Aa\) (gametes \(A\) and \(a\)) and \(aa\) (gametes \(a\)). Offspring genotypes: \(Aa\) (\(A\times a\)) and \(aa\) (\(a\times a\)). Not all heterozygous.

Answer:

\(AA\times aa\)