Practice question

Presence of all dominant phenotypes in F1 generation indicates each offspring inherited at least one dominant allele from parents. Cross between homozygous dominant AA and homozygous recessive aa obligately produces heterozygotes Aa for monohybrid trait, all dominant phenotypically despite carrying recessive allele genotypically. Other crosses such as both heterozygous produce recessive segregants, and both homozygous dominant produce no recessive tester. Uniform dominant F1 therefore signals parental genotypes were contrasting pure-breeding lines, typical starting point for Mendel monohybrid experiments establishing dominance relationship and segregation in subsequent F2.