Final answer:
Dominant traits are expressed in individuals with homozygous dominant (AA) and heterozygous (Aa) genotypes, while recessive traits are only expressed in homozygous recessive (aa) genotypes. Homozygous refers to having two identical alleles, and heterozygous means having one dominant and one recessive allele.
Step-by-step explanation:
In genetics, a dominant trait is one that is expressed in both the homozygous dominant genotype (AA) and the heterozygous genotype (Aa). A dominant allele masks the presence of the recessive allele in an organism's phenotype, meaning that the recessive trait is not visibly expressed. Conversely, a recessive trait will only be observed in individuals that are homozygous recessive (aa), as the presence of a dominant allele (A) would overshadow the recessive allele (a).
An individual with two identical alleles, either both dominant (AA) or both recessive (aa), is considered to be homozygous. Those with one dominant and one recessive allele (Aa) are referred to as heterozygous. In Mendelian genetics, the dominant trait will be expressed in both homozygous dominant and heterozygous individuals, meaning they will have different genotypes but the same phenotype, while the recessive trait will only manifest in homozygous recessive individuals.