Question

In a cross of a homozygous dominant parent and a homozygous recessive parent, what is the ratio of offspring that will exhibit the recessive phenotype

Answer 1

In a cross between a homozygous dominant parent and a homozygous recessive parent, all F1 offspring will show the dominant phenotype. Therefore, the ratio of offspring exhibiting the recessive phenotype is 0:1 in the F1 generation, with none displaying the recessive trait.

Step-by-step explanation:

In a cross between a homozygous dominant parent and a homozygous recessive parent, all of the offspring in the first generation (F1) will exhibit the dominant phenotype. This is because the presence of even one dominant allele masks the expression of the recessive allele. However, in this scenario, the offspring would all be heterozygous carriers of the recessive trait.

When considering the ratio of offspring exhibiting the recessive phenotype, it's important to note that in such a cross, none of the F1 generation will show the recessive phenotype, since they are all heterozygous (carrying one dominant and one recessive allele). Therefore, the ratio of offspring that will exhibit the recessive phenotype in the F1 generation is 0:1 (or simply 0%, since none will display the recessive trait).

If these heterozygous F1 offspring were then to be crossed with each other (self-crossed), the resulting F2 generation would follow a 3:1 phenotypic ratio, with three quarters showing the dominant phenotype and one quarter showing the recessive phenotype, as per Mendelian genetics.

Answer 2

Assuming complete dominance, *none* of the offspring will exhibit the recessive phenotype. If A is dominant to a, then the cross between a homozygous dominant parent (AA) and a homozygous recessive parent (aa) would produce offspring all sharing the same genotype (Aa, or all heterozygous).

Because A is assumed to be completely dominant over a, only those individuals with the aa genotype would exhibit the recessive phenotype.