Meiotic drive

From EvoWiki

Meiotic drive (also called segregation distortion) is any process which causes one gametic type to be over- or under-represented in the gametes formed during meiosis, and hence in the next generation.

A classic example of meiotic drive is the T locus in mice. This locus affects tail length and viability. TT homozygotes have normal long tails; Tt heterozygotes have short tails and transmit ~ 90% of the t allele to their sperm; tt homozygotes are sterile. Meiotic drive will increase frequency of the t allele to point where that become frequent enough to occur as tt homozygotes with appreciable frequency, whereupon selection works against t alleles. This shows two levels selection: positive selection for t haplotypes at the level of the gene, negative selection for tt individuals at the level of the genotype (organism).

The T locus (T/t complex) is indeed the best understood example of meiotic drive in mammals. However, the phenotypes of the T locus as presented in the text above are wrong. T/T homozygosity is embryonic lethal. Not only tail is missing but whole distal part of the body is disorganized. Tt mice are viable but have no tails. Tt males but not females transmit the t allele to 90% or more of their offspring. Finally, the tt homozygotes can be either lethal or viable. If viable, they can be either sterile (again only males) or fertile, all depending on the combination of particular t alleles (more properly t haplotypes)