1. exhibiting resemblance based on common ancestry (see homology).

2. describing chromosomes that are identical in terms of their visible structure and location of gene segments, although they may carry different alleles. Diploid organisms, such as humans, possess homologous pairs of chromosomes (see autosome) in the nuclei of their body cells. See also recombination.

3. describing any segment of a nucleic acid (DNA or RNA) or protein whose sequence of, respectively, bases or amino acids is similar to that of another segment.