In a single-gene trait with complete dominance, what phenotypic ratio is produced in an Aa × Aa cross?

In a single-gene trait with complete dominance, what phenotypic ratio is produced in an Aa × Aa cross?

• A. 1 dominant : 3 recessive.
• B. 2:2
• C. 3 dominant : 1 recessive.
• D. 1:1

Answer: (C)

In a monohybrid cross with complete dominance, the dominant phenotype appears whenever at least one dominant allele is present. Crossing two Aa individuals means each parent can pass on A or a, producing offspring genotypes AA, Aa, Aa, and aa. The dominant phenotype shows up in AA and Aa (three out of four), while the recessive phenotype appears only in aa (one out of four). So the phenotypic ratio is 3 dominant : 1 recessive.

In a monohybrid cross with complete dominance, the dominant phenotype appears whenever at least one dominant allele is present. Crossing two Aa individuals means each parent can pass on A or a, producing offspring genotypes AA, Aa, Aa, and aa. The dominant phenotype shows up in AA and Aa (three out of four), while the recessive phenotype appears only in aa (one out of four). So the phenotypic ratio is 3 dominant : 1 recessive.