A monohybrid cross involves one trait and typically yields which phenotypic ratio for a single-gene trait?

A monohybrid cross involves one trait and typically yields which phenotypic ratio for a single-gene trait?

• A. 3:1
• B. 1:1
• C. 9:3:3:1
• D. 2:1

Answer: (A)

In a monohybrid cross for a single gene with two alleles, when both parents are heterozygous, the dominant trait is expressed in about three of the four offspring and the recessive trait in about one. This comes from the possible offspring genotypes: AA, Aa, Aa, and aa. The dominant phenotype appears in AA and Aa (three occurrences), while the recessive phenotype appears only in aa (one occurrence). So the typical outcome is three showing the dominant trait for every one showing the recessive trait. If you start with true-breeding lines (AA and aa) and cross them, the first generation is all Aa, and crossing two such offspring yields the same 3:1 phenotypic pattern in the next generation. Note this three-to-one pattern relies on complete dominance; other inheritance patterns can shift the ratio.

In a monohybrid cross for a single gene with two alleles, when both parents are heterozygous, the dominant trait is expressed in about three of the four offspring and the recessive trait in about one. This comes from the possible offspring genotypes: AA, Aa, Aa, and aa. The dominant phenotype appears in AA and Aa (three occurrences), while the recessive phenotype appears only in aa (one occurrence). So the typical outcome is three showing the dominant trait for every one showing the recessive trait. If you start with true-breeding lines (AA and aa) and cross them, the first generation is all Aa, and crossing two such offspring yields the same 3:1 phenotypic pattern in the next generation. Note this three-to-one pattern relies on complete dominance; other inheritance patterns can shift the ratio.