What does it mean if an organism is homozygous?

An organism is described as homozygous when it possesses two identical alleles for a specific gene. This can occur for any gene locus where the organism inherits the same variant (allele) from both parents. For example, if both alleles for a trait are the same, such as two copies of the dominant allele (AA) or two copies of the recessive allele (aa), that organism is considered homozygous for that gene.

Being homozygous can significantly affect the organism's phenotype, as the identical alleles will express either a dominant or a recessive trait consistently. This uniformity can lead to predictable outcomes in traits being studied in genetics, making it an important concept in understanding heredity and the expression of traits. The other options focus on different genetic configurations or concepts that do not align with the specific definition of homozygosity.