Editing Chromosomal crossover (section)

==Consequences==
[[Image:Conversion and crossover.jpg|thumb|right |upright=1.15|The difference between [[gene conversion]] and chromosomal crossover.]]
In most [[eukaryote]]s, a [[cell (biology)|cell]] carries two versions of each [[gene]], each referred to as an [[allele]]. Each parent passes on one allele to each offspring. An individual [[gamete]] inherits a complete haploid complement of alleles on chromosomes that are independently selected from each pair of [[chromatid]]s lined up on the metaphase plate. Without recombination, all alleles for those genes linked together on the same chromosome would be inherited together. [[Meiotic non-disjunction|Meiotic]] recombination allows a more independent [[Segregation (materials science)|segregation]] between the two alleles that occupy the positions of single genes, as recombination shuffles the allele content between homologous chromosomes.{{cn|date=December 2024}}

Recombination results in a new arrangement of maternal and paternal alleles on the same chromosome. Although the same genes appear in the same order, some alleles are different. In this way, it is theoretically possible to have any combination of parental alleles in an offspring, and the fact that two alleles appear together in one offspring does not have any influence on the [[Statistical hypothesis testing|statistical]] [[probability]] that another offspring will have the same combination. This principle of "[[Mendelian inheritance|independent assortment]]" of genes is fundamental to genetic inheritance.<ref name = "Darling">{{cite web |url=http://www.daviddarling.info/encyclopedia/G/genetic_recombination.html |title=Genetic recombination | vauthors = Darling D }}</ref>
However, the frequency of recombination is actually not the same for all gene combinations. This leads to the notion of "[[centiMorgan|genetic distance]]", which is a measure of recombination [[frequency]] averaged over a (suitably large) sample of [[Genealogy|pedigrees.]] Loosely speaking, one may say that this is because recombination is greatly influenced by the proximity of one gene to another. If two genes are located close together on a chromosome, the likelihood that a recombination event will separate these two genes is less than if they were farther apart. [[Genetic linkage]] describes the tendency of genes to be inherited together as a result of their location on the same chromosome. [[Linkage disequilibrium]] describes a situation in which some combinations of genes or genetic markers occur more or less frequently in a population than would be expected from their distances apart. This concept is applied when searching for a gene that may cause a particular [[disease]]. This is done by comparing the occurrence of a specific [[DNA sequence]] with the appearance of a disease. When a high correlation between the two is found, it is likely that the appropriate gene sequence is really closer<ref name = "Darling" />