What is true about homologous chromosomes?

• A. They carry the same genes at the same loci, but may carry different alleles
• B. They are identical copies
• C. They determine the sex chromosomes only
• D. They are non-homologous

Answer: (A)

Homologous chromosomes are a matched pair: they carry the same genes in the same order (same loci), one inherited from each parent. They may differ in the versions of those genes, called alleles, so the two chromosomes can carry different alleles for the same gene. They are not identical copies—that would be sister chromatids, which are duplicates of the same chromosome after DNA replication and stay joined until later stages. They aren’t limited to sex chromosomes; most chromosome pairs are homologous. During meiosis, homologous chromosomes pair up and can exchange genetic material through crossing over, adding to genetic variation. So the statement that they carry the same genes at the same loci, but may carry different alleles, captures their defining feature.