What is the definition of a homozygous organism?

• A. An organism with two different alleles for a trait
• B. An organism that has two identical alleles for a trait
• C. An organism that has only one allele for a trait
• D. An organism that has no alleles for a trait

Answer: (B)

A homozygous organism is defined as one that possesses two identical alleles for a specific trait. This means that both alleles inherited from each parent are the same, which can be either dominant or recessive. For example, if an organism has two dominant alleles (AA) or two recessive alleles (aa) for a particular gene, it is classified as homozygous for that trait. This genetic uniformity can significantly influence the expression of traits and is essential for understanding inheritance patterns, particularly in breeding and genetics.

In contrast, the other options describe different genetic conditions. An organism with two different alleles for a trait is known as heterozygous. An organism that has only one allele for a trait would suggest incomplete dominance or might indicate a lack of genetic variation influencing that trait. An organism with no alleles for a trait is not possible in typical genetics since traits are defined by the presence of alleles. Thus, the definition of homozygous focusing on identical alleles is clearly the key point, solidifying the understanding of genetic terminology.