In a monohybrid cross between two homozygous parents (one dominant and one recessive), what is the expected phenotype of the F1 offspring?

• A. All offspring will display the dominant phenotype and be uniform.
• B. All offspring will display the recessive phenotype.
• C. The offspring will show a 3:1 ratio of dominant to recessive phenotypes.
• D. Half of the offspring will display the dominant phenotype, and half will display the recessive phenotype.

Answer: (A)

Verified step by step guidance

1. Identify the genotypes of the two homozygous parents. One parent is homozygous dominant (e.g., \(AA\)) and the other is homozygous recessive (e.g., \(aa\)).
2. Determine the genotype of the F1 offspring by performing the cross: \(AA \times aa\). Each offspring receives one allele from each parent, so all F1 genotypes will be heterozygous (\(Aa\)).
3. Recall that in a monohybrid cross, the dominant allele masks the recessive allele in heterozygous individuals, so the phenotype of \(Aa\) will be the dominant trait.
4. Conclude that since all F1 offspring have the genotype \(Aa\), they will all display the dominant phenotype and be uniform in appearance.
5. Understand that this result differs from a typical 3:1 ratio, which appears in the F2 generation after crossing two heterozygous F1 individuals.