That said, some sex-determining alleles do achieve high frequencies. Model and results We formulate a population genetics model consisting of three loci with an arbitrary number of alleles at each locus. The new sex-determining allele fares better than the resident allele, which leaves sex determination to environmental cues and suffers the viability costs associated with its linked allele half of the time.
Here, we provide an alternative explanation for the origin of sex chromosomes that relies on a sex-determining allele benefiting from meiotic drive.
This gene is called the SRY gene. Utrecht University - Department of Biology. Sharat The sex chromosome associated with female characteristics in mammals, occurring paired in the female and single in the male. The X and Y chromosomes have small regions of homology called pseudoautosomal regions.
It turns out that the sex determination pathway is probably more complicated and SRY may in fact inhibit some anti-male genes. Stevens and the Discovery of Sex Determination by Chromosomes". By signing up, you agree to our Privacy Notice. When any of the 9 genes involved in sperm production are missing or defective the result is usually very low sperm counts and infertility.
If the suppressor were to arise earlier, then there would be no way for a later-arising sex-determining allele to use the driver to ride to high frequency. Received Aug 5; Accepted Oct Charlesworth B. Whether linked sex-determining mutations or drive-suppressor mutations are more likely to arise by mutation is an empirical question.
In step 3, a rare suppressor of male drive, C 2is introduced at a locus that freely recombines with the drive locus. Specify the sex chromosome pairs for male and female mammals in Surrey, despite much previous work that examines meiotic drive's influence on sex determination, its potential role in the origin of genetic sex determination and sex chromosomes has not, to our knowledge, ever been explored.
At this equilibrium, the heterogametic males preferentially transmit the male-determining allele, thus maintaining a male-biased sex ratio.
Note that A 2 is absent from eggs because it is a dominant male-determining allele figure 2. Proc Biol Sci. Within each plot the frequency of adult males in the population is depicted on the horizontal axis. Two previous theories for the origin of sex chromosomes have, respectively, sought to answer these questions.
Genetic load, drive and sex determination.