When the alleles of a gene pair are different, how are they described?

When the alleles of a gene pair are different, they are described as heterozygous. This term derives from the Greek prefix "hetero," meaning different, and "zygos," meaning yoke or pair. In a heterozygous configuration, one allele may be dominant while the other is recessive, but what defines this state is the presence of two different alleles at the same locus on homologous chromosomes.

This genetic variation can lead to different expressions of traits or characteristics, depending on the dominance relationships between the alleles. For instance, if one allele codes for brown eyes and the other for blue eyes, a heterozygous individual will exhibit the characteristic associated with the dominant allele, which in this example would be brown eyes.

Homozygous refers to when the alleles are the same, either both dominant or both recessive. Recessive and dominant signify the behavior of alleles in terms of their expression rather than describing the configuration of the alleles themselves. Thus, the terminology used here is specific to the allelic configuration, making heterozygous the appropriate choice when discussing different alleles of a gene pair.