What does the term heterozygous mean?

The term heterozygous refers specifically to an organism having two different alleles for a given trait. In genetics, alleles are different versions of a gene that can govern specific characteristics. For example, if one allele codes for blue eye color and another for brown eye color, an individual with one of each would be considered heterozygous for that trait. This genetic diversity can lead to variation in traits among individuals and is fundamental in the study of inheritance.

In contrast, having two identical alleles would denote a homozygous condition, which is not characterized as heterozygous. The concept of having no alleles can be misleading, as every trait is typically inherited from parents. More than two alleles for a trait refers to a different concept known as multiple alleles, which is not the same as being heterozygous, as heterozygous specifically involves just two different versions of a gene.