Homologous chromosome
Encyclopedia : H : HO : HOM : Homologous chromosome
Homologous chromosomes are non-identical chromosomes that contain information for the same biological features. In diploid organisms (most plants and animals), each homologous chromosome is inherited from a different parent. Polyploid cells, however, have more than two homologous chromosomes.
Homologous chromosomes contain the same genes at the same loci (e.g., both have genes encoding eye colour), but these genes may contain different genetic information or alleles (e.g. one may code for brown eyes, one may code for blue).
In humans, for example, there are 46 chromosomes—23 homologous pairs of chromosomes in females and 22 homologous pairs in males (males have X+Y chromosomes which are not homologous but females have two X chromosomes which are homologous). Chromosomes which are not sex chromosomes are called autosomes. Humans inherit 22 pairs of autosomes from their parents (one from each) along with two sex chromosomes. Only females, however, have homologous sex chromosomes; males have X+Y.
Homologous chromosomes are similar in length, except for sex chromosomes in several taxa, wherein the X chromosome is considerably larger than the Y chromosome. These chromosomes share only small regions of homology.
Homologous chromosomes are not to be confused with sister chromatids, the exactly identical chromosomes that are found separating during mitosis or meiosis II.
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