What are homologous chromosomes?

• A. Chromosome pairs that carry the same genes at the same loci, one from each parent
• B. Identical copies of a chromosome
• C. Sex chromosomes only
• D. Chromosomes with the same length but different genes

Answer: (A)

Homologous chromosomes are pairs of chromosomes that carry the same genes in the same order at the same positions (loci), with one member of the pair coming from each parent. They are similar in size and gene content, but may carry different versions (alleles) of those genes. They pair up during meiosis to allow crossing over, which creates genetic variation.

This isn’t about identical copies—that would be sister chromatids, which are the two identical copies of a chromosome produced during DNA replication and held together until later stages. It isn’t limited to sex chromosomes, since homologous pairs exist for all autosomes as well (though humans may have X–X as a homologous pair, many homologous pairs are autosomal). And it isn’t simply about length being the same; they must carry the same genes at the same loci, not just be similar in size.