What are chromosomes that come in pairs called?

Chromosomes that come in pairs are referred to as homologous chromosomes. This term describes a pair of chromosomes, one inherited from each parent, that are similar in shape, size, and genetic information. Homologous chromosomes contain the same genes at the same loci but may carry different alleles, or variants, of those genes. This pairing is crucial during meiosis, the process of cell division that produces gametes, as it allows for genetic recombination and proper segregation of genes.

In contrast, identical chromosomes refer to replicated chromosomes during cell division when sister chromatids are present, which are exact copies of the original chromosome. Sex chromosomes, on the other hand, are specifically the chromosomes that determine an organism's sex (e.g., XX or XY in humans), and they do not refer to all pairs of chromosomes in the genome. Sister chromatids are not considered pairs in the context of homologous chromosomes because they represent two identical copies of a single chromosome formed after DNA replication, rather than being a matched set from two different parents. Thus, homologous chromosomes accurately describe chromosome pairs in genetics.