Mendelian Link Practice Test

In a monohybrid cross, the expected phenotypic ratio is indeed 3:1. This ratio arises from crossing two heterozygous individuals for a single trait, where one allele is dominant and the other is recessive.

To illustrate this, consider a trait where the dominant allele is represented by "A" and the recessive allele by "a." If you cross two individuals that are both heterozygous (Aa x Aa), the possible combinations of alleles in the offspring can be visualized using a Punnett square. The outcome shows that there are four possible genotypes: AA, Aa, Aa, and aa.

- The dominant phenotype (AA and Aa) appears in three out of the four offspring.

- The recessive phenotype (aa) appears in one out of the four offspring.

Thus, when considering observable traits (phenotypes), three offspring will display the dominant trait, and one will display the recessive trait, resulting in a ratio of 3:1 for the phenotypes. This foundational concept in genetics highlights how dominant traits can overshadow recessive traits in the offspring of heterozygous parents.

The other ratios listed correspond to different genetic crosses or scenarios: 1:1 is seen in