Crossing over is a fundamental process in genetics that is responsible for genetic variation during the formation of gametes in sexual reproduction. It is a process that occurs during meiosis in which homologous chromosomes exchange genetic material. During crossing over, parts of the maternal and paternal chromosomes are exchanged, thus creating novel combinations of alleles which are inherited by the offspring. This process is ultimately responsible for the phenomenon of genetic recombination and the generation of novel genotypes that are seen in the progeny of sexually reproducing organisms.
Crossing over was first observed by Thomas Hunt Morgan in 1910 in fruit flies (Morgan, 1910). He observed that the segregation of genetic traits in the progeny of a given parental generation were often different from the parental genotype, indicating a process of genetic recombination must have occurred. Subsequent research has identified the mechanism by which crossing over occurs. During meiosis, homologous chromosomes pair together in a process known as synapsis. In this process, regions of homology between the maternal and paternal chromosomes are identified, and a cross-over event is initiated that leads to the exchange of genetic material between them (Fry, 2020). This exchange occurs at chiasmata, which are sites of physical connections between homologous chromosomes. After the exchange of genetic material, the homologous chromosomes separate, and the recombined genetic material is transmitted to the progeny.
Crossing over is an essential process for the generation of genetic variation in sexually reproducing organisms, and it is especially important in species with large, complex genomes. Studies of species with large genomes, such as humans, have demonstrated that the majority of genetic variation is generated by the processes of crossing over (Hudson, 1999). This variation is important for the development of new traits and for the species’ ability to adapt to changing environments.
Crossing over is an essential process in genetics that is responsible for genetic variation during the formation of gametes in sexual reproduction. It was first observed by Thomas Hunt Morgan in 1910, and subsequent research has identified the mechanism by which it occurs. This exchange of genetic material is responsible for the phenomenon of genetic recombination and the generation of new allelic combinations that are inherited by the offspring. Crossing over is especially important in species with large, complex genomes, as it is responsible for the majority of genetic variation in these species.
References
Fry, D.B. (2020). Crossing over. In Encyclopedia Britannica. Retrieved from https://www.britannica.com/science/crossing-over
Hudson, R. R. (1999). Generating samples under a Wright-Fisher neutral model of genetic variation. Bioinformatics, 15(3), 175–188. https://doi.org/10.1093/bioinformatics/15.3.175
Morgan, T.H. (1910). Sex-limited inheritance in Drosophila. Science, 32(822), 120–122. https://doi.org/10.1126/science.32.822.120