Similarly, so-called "segregation distorter
genes" will chemically sabotage the allele with which they are paired on the chromosome, even if it results in a less fit--in this case sterile--organism.
For example, in Drosophila melanogaster, segregation distorter (SD), a meiotic drive system, results in transmission of the SD chromosome in vast excess over the normal S[D.sup.+] homolog in heterozygous SD/S[D.sup.+] males (Powers and Ganetzky, 1991).
Abbreviations: CMS, cytoplasmic male sterility; ML, maximum likelihood; PCR, polymerase chain reaction; RAPD, random amplified polymorphic DNA: SD, segregation distorter.
A significant number of species which reproduce sexually are known to possess segregation distorter genes (SDs), which operate during meiosis, the process of cell division through which gametes (eggs and sperm) are created.
This seems a paradigmatic case of selection; having the trait of being a segregation distorter increases the chances of a bit of genetic material's being passed on through generations as compared with other genes without the trait.
14 Interestingly, it turns out that if we take the gene itself as a real biological system, then segregation distorter genes can be analysed into parts which have functions relative to the segregation distorter gene.
Chromosomes bearing the SD segregation distorter
There are nine chapters, covering self-replicating automata and what they tell us about the evolution of life (with an extensive discussion of Conway's computer game, Life), population dynamics (including Lotka-Volterra models, chaos, simple 3-trophic level systems, and island biogeography), population genetics (random drift, Mendelian genetics, the evolution of dominance, and segregation distorters
), the evolution of sex (runaway selection, the good genes hypothesis, why sex, why a 1:1 sex ratio, and why primarily two sexes?), and game theory (alternative mating tactics, the hawk-dove game, a chapter devoted entirely to cooperation and the Prisoner's Dilemma).
The competition between several sex-specific segregation distorters has never been modeled explicitly (but see Hartl 1970; Liberman 1991).
Figure 2 shows more systematically for which segregation distorters stable coexistence is possible.
We conclude that complementation is a potent force enhancing the coexistence of segregation distorters and that coexistence of two distorters is only precluded if there is no complementation at all.
Competition between Segregation Distorters in a Structured Metapopulation