Homologous chromosomes

Definition

A matched pair of chromosomes—one inherited maternally, one paternally—that carry the same genes at corresponding loci and pair (synapse) during meiosis I. Their alignment enables crossing-over and proper segregation, forming the physical basis of Mendelian inheritance. In diploid arthropods, homolog number defines the haploid chromosome count (n); divergence between homologs can indicate incipient speciation or polyploidy.

Etymology

From Greek homologos (agreeing, corresponding), with chromosome (colored body) coined by Waldeyer, 1888.

Example

In Drosophila melanogaster, females possess four pairs of homologous chromosomes (three autosomal pairs plus XX), while males have mismatched sex chromosomes (XY) that pair only at their pseudoautosomal regions during meiosis.

Synonyms

• homologs

Related Terms

• Chromosome
• Meiosis
• synapsis
• crossing-over
• karyotype
• autosome
• Sex chromosome
• alleles
• diploidy
• haploid

Usage Notes

Distinguished from sister chromatids (identical copies joined at the centromere after replication). In polyploid insects and some arachnids, 'homologous' may refer to more than two chromosomes sharing the same gene content. The term applies to any diploid or higher-ploid cell; haploid cells and most male Hymenoptera lack homologous pairs.