[6][7][8] Autosomic genes usually have the same mode of transmission in sexually reproducing species due to the fairness of Mendelian segregation, but conflicts among alleles of autosomic genes may arise when an allele cheats during gametogenesis (segregation distortion) or eliminates embryos that do not contain it (lethal maternal effects).
Finally, mobile genetic elements completely bypass Mendelian segregation, being able to insert new copies of themselves into new positions in the genome (transposons).
One example is a gene drive complex, called a segregation distorter, that "cheats" during meiosis or gametogenesis and thus is present in more than half of the functional gametes.
The most studied examples are sd in Drosophila melanogaster (fruit fly),[9] t haplotype in Mus musculus (mouse) and sk in Neurospora spp.
Other systems do not involve gamete destruction, but rather use the asymmetry of meiosis in females: the driving allele ends up in the oocyte instead of in the polar bodies with a probability greater than one half.
In some cases, there is strong evidence to support the contention that they are simply selfish and that they exist as parasitic chromosomes.
[18] Mitochondria and chloroplasts are two examples of sets of cytoplasmic genes that commonly have exclusive maternal inheritance, similar to endosymbiont parasites in arthropods, like Wolbachia.
Because of this fact, cytoplasmic genes have evolved a number of mechanisms to increase the production of female descendants and eliminate offspring not containing them.
[20] Male organisms are converted into females by cytoplasmic inherited protists (Microsporidia) or bacteria (Wolbachia), regardless of nuclear sex-determining factors.
In certain haplodiploid Hymenoptera and mites, in which males are produced asexually, Wolbachia and Cardinium can induce duplication of the chromosomes and thus convert the organisms into females.
If antibiotics are administered to populations which have become asexual in this way, they revert to sexuality instantly, as the cytoplasmic bacteria forcing this behaviour upon them are removed.
In many arthropods, zygotes produced by sperm of infected males and ova of non-infected females can be killed by Wolbachia or Cardinium.