Homologous chromosomes
homologous chromosomes (a pair of homologous chromosomes form a bivalent ) are Chromosome S pertaining to the same pair, of the same size having same genes but not obligatorily same the Allèles. At the organizations Diploïde S, one of the homologous chromosomes is of maternal origin, the other of paternal origin.
At the man, in the somatic cells, there are 22 pairs of homologous (known as chromosomes autosomes ), numbered chromosomes 1 with 22 and a pair of chromosomes sexual (called heterochromosomes or Gonosome S: XY at the man, XX at the woman). Both X chromosomes of the woman are of course homologous but the Y chromosome is homologous only in one small area with X chromosome (= pseudo-autosomiques areas).
If the homologous chromosomes carry same genes, that does not mean that they code same the genetic Information since the same paternal and maternal gene can present change S: one speaks then about Allèle S. During the Meiosis, the homologous chromosomes pair and exchange fragments of bit mixing genes with maternal alleles with genes with the paternal alleles. It is the phenomenon of Crossing-over or intra-chromosomal recombination or crossing-over, which generate important a genetic Diversité. Genetic recombination, as well as the random restocking of the chromosomes will provide an important source of diversity which makes it possible to the populations Eucaryote S to adapt to the environmental conditions.
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