Genetic recombination or chromosomal crossover is when chromosomes or regions of the same chromosome exchange genetic information to produce new alleles. Alleles are different versions of the same genetic material. The main function of genetic recombination is to incorporate both genes of the male and female gamete, to boost genetic diversity within the offspring genome. Diversity from genetic recombination can increase the adaptability of organisms to survive in changing environment by increasing their fitness, and consequently survival. Another function of recombination is for DNA repair in cellular processes and fighting pathogens. There are two main types of genetic recombination: general and site-specific.
General recombination refers to transfer of DNA between homologous chromosomes, this process is exemplified in meiosis. Chromosomes that undergo crossover are usually homologous – similarities in position, size, and centromere placement. After fertilization of the ova, the nuclear envelope of the two gametes break down to expose the associated chromosomes. The homologous chromosomes migrate to the middle of the cell and line with a non-homologous chromosome, genetic recombination occurs when sections of DNA are transferred to each other to produce alleles connected by a chiasmata.
Site-specific recombination does not use homologous chromosomes but short nucleotide sequences1. Site-specific recombination can be seen in the adaptive immune system, it creates DNA-tailored antibodies that can respond to antigens in a foreign pathogen. Nucleotide sequences are transferred using recombination enzymes called recombinases.
1. Alberts, B., Bray,D., Lewis, J. et al. (1994). Genetic Recombination. Molecular Biology of the Cell (3rd ed.). New York, NY: Garland Science. Retrieved at http://www.ncbi.nlm.nih.gov/books/NBK28388/