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Chromosomal crossover, or crossing over, is the exchange of genetic material during sexual reproduction between two homologous chromosomes' non-sister chromatids that results in recombinant chromosomes.
Crossing over during meiosis, with chiasma shown. In genetics , a chiasma ( pl. : chiasmata ) is the point of contact, the physical link, between two (non-sister) chromatids belonging to homologous chromosomes .
The NCO/SDSA pathway contributes little to genetic variation, since the arms of the chromosomes flanking the recombination event remain in the parental configuration. Thus, explanations for the adaptive function of meiosis that focus exclusively on crossing-over are inadequate to explain the majority of recombination events.
Unequal crossing over is the process most responsible for creating regional gene duplications in the genome. [1] Repeated rounds of unequal crossing over cause the homogenization of the two sequences. With the increase in the duplicates, unequal crossing over can lead to dosage imbalance in the genome and can be highly deleterious. [1] [2]
Crossing over between the X and Y chromosomes is normally restricted to the pseudoautosomal regions; thus, pseudoautosomal genes exhibit an autosomal, rather than sex-linked, pattern of inheritance. So, females can inherit an allele originally present on the Y chromosome of their father.
In genetics, the crossover value is the linked frequency of chromosomal crossover between two gene loci ().For a fixed set of genetic and environmental conditions, recombination in a particular region of a linkage structure tends to be constant and the same is then true for the crossover value which is used in the production of genetic maps.
SDSA recombination does not cause crossing-over. In the process of crossing-over, genes are exchanged by the breaking and union of homologous portions of the chromosomes' lengths. [7] Structures called chiasmata are the site of the exchange. Chiasmata physically link the homologous chromosomes once crossing over occurs and throughout the ...
Crossing over requires a DNA double-stranded break followed by strand invasion of the homolog and subsequent repair. [3] Initiation sites for recombination are usually identified by mapping crossing over events through pedigree analysis or through analysis of linkage disequilibrium .