Homologous chromosomes are a matching pair of chromosomes containing the same genetic loci in the same order. One of the homologous chromosomes is received from the father, and the other is received from the mother.
Because there are two chromosomes in the pair, the pair contains two different alleles at every loci, one on each chromosome. This allows for a great deal of variation in individuals, by means of dominant traits, recessive traits, and polygenic traits, and masking genes. This type of variation, which accounts for the bulk of population diversity does not come from mutation, but the process known as genetic recombination.
Ordinarily, humans have 23 homologous pairs of chromosomes, for a total number of chromosomes (or diploid number) of 46. Down syndrome is a notable exception. People with Down syndrome have an extra 21st chromosome, giving them 22 homologous pairs of chromosomes and a single set of three.
- Homologous Chromosomes Biology Online