Homologous recombination

By Levi Clancy for Student Reader on
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During meiosis, homologous chromosomes are paired and aligned. This allows homologous recombination or crossing over to occur between the maternal and paternal derived chromosomes. Recombination or crossing over of these paired chromosomes increases genetic diversity in the offspring by associating maternal alleles with paternal on the same chromosome. Upon the division of meiosis I, recombinant chromosomes are segregated. After meiosis II to create haploid germ cells, these recombinant chromosomes are transmitted to progeny in haploid germ cells.

This pairing and recombination between homologous chromosomes also provides a mechanism for gene duplication when pairing occurs between repetitive sequences in the DNA. This pairing and recombination between homologous chromosomes also provides a mechanism for gene duplication when pairing can occur between repetitive sequences in the DNA. Gene duplication by unequal crossing-over between homologous repeats

Misalignment of the chromosomes during meiosis and crossing over in the wrong location yields two chromosomes. One has no copies of the beta globin gene and presumably leads to a recessive lethal phenotype. But the other recombinant chromosome has two functional copies of the gene. In this way, a small gene family has been created. These genes can evolve separately and ultimately come to have separate functions. Gene duplication as a result of unequal crossing-over between homologous chromosomes during meiosis can generate an array of homologous genes. Not all of these genes necessarily have the same function. Some may not be functional at all.