We call genetic recombination the random exchange of genetic material during meiosis, that is, the exchange of genes that happens between two nucleic acid molecules forming new combinations of genes on a chromosome. This process is responsible for mixing the different genes of living beings, making evolution possible.
The recombination, as well as the mutation, act together for the evolution of the species. While recombination mixes the modified parts of DNA from two organisms, the mutation is responsible for this modification in the DNA.
As it happens?
When we have two chromosomes that break and unite again, there is an exchange of the genes carried by these chromosomes, which in genetics we call crossing over, the process of the first meiotic division, more precisely in the pachytene. This process is nothing more than the sub-crossing of homologous non-sister chromatids that are side by side. With that, the chromosomes recombine, carrying, from then on, part of the genes of the other.
This process leads to the formation of daughter cells that have a different constitution than the mother cell.
In this recombination, the homologous chromosomes cross, being able to unite at certain points called chiasms, making it possible for the chromosomal segments to exchange with certain blocks of genes, always between the homologous members of the pairs.
What are the consequences?
Derived from this process of gene recombination, there are consequences that can be several. When in asexual organisms, genes are inherited together or linked, since genes from other organisms cannot be mixed in them during reproduction. In the sexed ones, in turn, there is a random mixing of the parents’ chromosomes, originated by chromosomal segregation.
In this process of gene recombination, a DNA exchange takes place between homologous chromosomes of the sexed organisms, and this shuffling process allows the alleles, even if close, in a DNA chain to secrete independently.
This, however, happens about one recombination event for every million base pairs, when in humans, and so the nearby genes on a chromosome are generally not separated and, consequently, tend to be inherited together. We call a haplotype the set of alleles that are usually inherited together, and this “co-inheritance” may mean that the locus is under a selection considered positive.