Segregation distorters

Lyttle, TW,  Annual Review of Genetics,  25:511-557. 1991.

Segregation distorters are genetic elements that exhibit the phenomenon of meiotic drive; that is, the mechanics of the meiotic divisions cause one member of a pair of heterozygous alleles or heteromorphic chromosomes to be transmitted to progeny in excess of the expected Mendelian proportion of 50% ( 1 34 , 1 36). In this review, we refer to these as genic or chromosomal drive, respectively. Genic meiotic drive is initially limited in its impact to the population dynamics of the drive locus itself and those loci fortuitiously in close linkage. Alleles at these latter loci may enjoy indirect drive through genetic hitchhiking, leading eventually to the establishment of drive haplotypes (64). The haplotype may be extended by incorporating chromosome rearrangements that reduce recombination and promote further linkage disequilibrium between the drive locus and more distant modifier loci ( 1 04 , 1 28, 1 64). In the extreme , the haplotype becomes coextensive with the chromosome, leading to a form of chromosomal meiotic drive. For a parent heterozygous for either type of drive system, the statistic k is used to denote the proportion of progeny (and by inference, successful gametes) that carry the allele or chromosome exhibiting segregation distortion. Thus , k can vary from 0 . 5 (Mendelian segregation segregation) to 1 .0 (complete segregation distortion with only one gamete class recovered in the progeny) .