Question

what should you expect to observe from a dihybrid cross of two individuals with different alleles for each characteristic?
a. an ( f_{2} ) generation that shows only the dominant phenotype for each trait
b. an ( f_{1} ) generation that shows only the dominant phenotype for each trait
c. an ( f_{2} ) generation that shows only the dominant phenotype for each trait, but an ( f_{1} ) generation that includes both phenotypes
d. ( f_{1} ) and ( f_{2} ) generations that show only the dominant phenotype for each trait

Explanation:

When two individuals with different alleles for each characteristic (e.g., \(AaBb\times AaBb\)) are crossed in a dihybrid cross:

• According to Mendel's laws, in the \(F_1\) generation (first - filial generation), assuming complete dominance, all offspring will show the dominant phenotype for each trait. For example, if \(A\) is dominant over \(a\) and \(B\) is dominant over \(b\), the \(F_1\) generation from \(AA BB\times aa bb\) (parental cross) will be \(Aa Bb\) (showing dominant phenotypes for both traits).
• In the \(F_2\) generation (second - filial generation, obtained by self - crossing \(F_1\) individuals like \(Aa Bb\times Aa Bb\)), using the Punnett square or the product rule (\((3:1)\times(3:1) = 9:3:3:1\) phenotypic ratio), there will be a variety of phenotypes. But the \(F_1\) generation (from a cross like \(AA BB\times aa bb\)) shows only the dominant phenotype for each trait.

Answer:

B. An \(F_1\) generation that shows only the dominant phenotype for each trait