doublecrossover

Double crossover refers to a genetic recombination event during meiosis in which two crossover events occur in the same chromosomal region between loci. The two crossovers effectively exchange the segment between the loci twice, so the middle portion is typically restored to its original parental configuration while the flanking regions are redistributed relative to the parental haplotypes. Because the middle segment is often left unchanged, double crossovers are rarer than single crossovers and can be more difficult to detect by simple phenotypic observation alone.

In genetic mapping, double crossovers are especially informative. They help reveal the order and relative distances of three or more loci along a chromosome. For example, in a three-locus cross, a double crossover between the outer loci can produce recombination in the outer intervals while leaving the middle marker in the parental state, a pattern that aids determining locus order. Detecting these events typically requires analyzing a large number of offspring from a heterozygous individual and is most effectively interpreted through multi-locus (three-point or higher) mapping approaches.

Frequency of double crossovers is several-fold lower than that of single crossovers, which means their discovery depends on sample size and the density of informative markers. Despite their rarity, double crossovers provide valuable constraints on gene order and chromosomal distances, contributing to more accurate genetic maps.