Here's why:
* Simple dominance: In simple dominance, one allele (the dominant allele) masks the expression of the other allele (the recessive allele).
* Homozygous dominant: This means the organism has two copies of the dominant allele (e.g., AA).
* Heterozygous: This means the organism has one copy of the dominant allele and one copy of the recessive allele (e.g., Aa).
Example:
Let's say the trait is flower color, where "A" represents the dominant allele for purple flowers and "a" represents the recessive allele for white flowers.
* AA: The plant will have purple flowers.
* Aa: The plant will also have purple flowers because the dominant "A" allele masks the "a" allele.
Therefore, both homozygous dominant (AA) and heterozygous (Aa) individuals will have the same phenotype, purple flowers.
It's important to note that this only applies to traits controlled by simple dominance. In other inheritance patterns, such as incomplete dominance or codominance, this rule may not hold true.
