Explain why an organism with a homozygous dominant genotype has the same phenotype as an organism with a heterozygous genotype.

Answer 1

An organism's genotype refers to the genetic makeup or the combination of alleles it possesses for a certain gene or trait. On the other hand, an organism's phenotype refers to the physical characteristics or traits that are expressed as a result of its genotype.

In the context of genetics, a homozygous dominant genotype means that an organism carries two copies of the dominant allele for a specific gene, while a heterozygous genotype means that an organism carries one copy of the dominant allele and one copy of the recessive allele for the same gene.

In some cases, the presence of a dominant allele can override the expression of the recessive allele, resulting in the same phenotype for both homozygous dominant and heterozygous genotypes. This phenomenon is referred to as complete dominance.

For example, consider a gene that determines flower color in a certain plant species. Let's say that the dominant allele (A) leads to the expression of a red flower color, whereas the recessive allele (a) results in a white flower color.

If an organism has a homozygous dominant genotype (AA), it means that it possesses two copies of the dominant allele (AA). As the dominant allele is capable of overriding the recessive allele's expression, the organism will have the phenotype of red flowers.

On the other hand, if an organism has a heterozygous genotype (Aa), it means that it carries one copy of the dominant allele (A) and one copy of the recessive allele (a). Again, due to complete dominance, the presence of the dominant allele (A) will determine the phenotype, resulting in red flowers.

Therefore, even though the genotypes differ (AA vs. Aa), both organisms will exhibit the same phenotype (red flowers) because the dominant allele's expression masks the recessive allele's expression.