A theoretical-analysis of the effects of sex-chromosome aneuploidy on X-chromosome and Y-chromosome meiotic drive

Extra sex chromosomes are normally detrimental to the individual carrying them. In XY (or WZ) sex determining systems, an extra X chromosome in the homogametic sex generates enough X-autosome imbalance to usually cause inviability, or at least sterility. On the oth- er hand, extra Y chromosomes are some- times tolerated, although in mammals and other higher organisms where the Y is ac- tively involved in sexual development, XXY individuals are generally sterile. In Drosophila and perhaps other inverte- brates where the Y is largely genetically inert, a single extra Y may be permitted in both sexes, while two extra copies is only fertile in XXYY females (Cooper, 1956), if at all.