Final answer:
In a monohybrid cross with two heterozygous parents (Aa x Aa), the genotype ratio in the F1 offspring is 1:2:1 for AA: Aa: aa, and the phenotype ratio for a dominant-recessive trait is 3:1. The gametes produced by each parent will be 50% A and 50% a.
Step-by-step explanation:
Monohybrid Cross: Genotype and Phenotype Ratios
During a monohybrid cross involving two heterozygous (Aa) parents, the offspring (F1 generation) will exhibit a genotype ratio of 1:2:1 (AA: Aa: aa). This is because each parent can contribute either an A or a allele, resulting in these possible combinations. Consequently, the phenotype ratio for a trait that follows a simple dominant-recessive inheritance will be 3:1, with three-quarters expressing the dominant trait and one-quarter expressing the recessive trait assuming A is dominant over a.
The gametes produced by each parent will have either the A allele or the a allele. Considering a single trait and assuming each parent is Aa, the gametes will be 50% A and 50% a. When these gametes combine during fertilization, they can give rise to offspring with one of the three genotypes: AA, Aa, or aa.
For example, using pea plants with yellow seeds being dominant over green, when a homozygous YY plant (yellow seeds) is crossed with a homozygous yy plant (green seeds), all F1 offspring have the genotype Yy and display the yellow seed phenotype, representing a complete dominance scenario. Similarly, a cross between Yy (yellow seeds) parents will result in a 3:1 phenotypic ratio in the F2 generation (yellow to green seeds), given that the yellow seed trait is dominant.