What does a homozygous organism possess?

A homozygous organism possesses two identical alleles for a gene. This means that both copies of a particular gene—the one inherited from each parent—are the same. For example, if we consider a gene that affects flower color, a homozygous organism could have two alleles for purple flowers (PP) or two alleles for white flowers (pp). This uniformity in the genetic makeup can lead to consistent expression of traits, as there is no variability caused by different alleles.

In contrast, an organism with two different alleles for a gene is considered heterozygous, which introduces variation in trait expression because the different alleles may produce different effects depending on their dominance relationships. Having one allele for a trait would represent a different genetic scenario, often referred to as a hemizygous state in instances like sex-linked traits, particularly in males. Lastly, indicating that an organism has only dominant alleles does not accurately define homozygosity, as homozygous conditions can involve two recessive alleles as well. Thus, the defining feature of a homozygous organism is the presence of two identical alleles for a specific gene.