What is the expected phenotypic ratio of a monohybrid cross in complete dominance?

What is the expected phenotypic ratio of a monohybrid cross in complete dominance?

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

Answer: (B)

In a monohybrid cross exhibiting complete dominance, the expected phenotypic ratio is 3:1. This ratio arises when two parent organisms are crossed, with one being homozygous dominant for a trait (AA) and the other being homozygous recessive (aa). The offspring, or F1 generation, in this cross will all display the dominant phenotype (Aa). When these F1 individuals (Aa) are self-crossed, the resulting offspring (F2 generation) can be represented in a Punnett square. The combinations of alleles result in one homozygous dominant (AA), two heterozygous (Aa), and one homozygous recessive (aa). Therefore, the phenotypes observed are three individuals exhibiting the dominant trait (AA and Aa) and one showing the recessive trait (aa), yielding the phenotypic ratio of 3 dominant to 1 recessive: 3:1. This understanding of dominance and the resulting ratios is crucial in predicting genetic outcomes in breeding experiments and is a foundational concept in Mendelian genetics.

In a monohybrid cross exhibiting complete dominance, the expected phenotypic ratio is 3:1. This ratio arises when two parent organisms are crossed, with one being homozygous dominant for a trait (AA) and the other being homozygous recessive (aa). The offspring, or F1 generation, in this cross will all display the dominant phenotype (Aa).

When these F1 individuals (Aa) are self-crossed, the resulting offspring (F2 generation) can be represented in a Punnett square. The combinations of alleles result in one homozygous dominant (AA), two heterozygous (Aa), and one homozygous recessive (aa). Therefore, the phenotypes observed are three individuals exhibiting the dominant trait (AA and Aa) and one showing the recessive trait (aa), yielding the phenotypic ratio of 3 dominant to 1 recessive: 3:1.

This understanding of dominance and the resulting ratios is crucial in predicting genetic outcomes in breeding experiments and is a foundational concept in Mendelian genetics.