What is Haplodiploidy?
[[Image:Bees and Wasps.jpg|thumb|The haplodiploid sex-determination system is typical of wasps, bees and ants.]] '''Haplodiploidy''' is a [[sex determination]] system in which males develop from unfertilized eggs and are [[haploid]], and females develop from fertilized eggs and are [[diploid]].<ref>King R.C; Stansfield W.D. and Mulligan P.K. 2006. ''A dictionary of genetics''. 7th ed, Oxford University Press, p194. {{ISBN|0-19-530761-5}}</ref> Haplodiploidy determines the sex in ''all'' members of the [[insect]] order [[Hymenoptera]] ([[bee]]s, [[ant]]s, and [[wasp]]s), and the [[Thysanoptera]] ('thrips').<ref name=Grimaldi>Grimaldi D. and Engel M.S. 2005. ''The evolution of the insects''. Cambridge University Press. {{ISBN|0-521-82149-5}}</ref><sup>p408</sup><ref name=White84/> The system also occurs sporadically in some spider [[mite]]s, [[coleoptera]]ns (bark [[beetle]]s) and [[rotifer]]s. In this system, sex is determined by the number of sets of [[chromosome]]s an individual receives. An offspring formed from the union of a [[sperm]] and an [[egg (biology)|egg]] develops as a '''female''', and an unfertilized egg develops as a '''male'''. This means that the males have half the number of chromosomes that a female has, and are [[haploid]]. The haplodiploid sex-determination system has a number of peculiarities. Most importantly, the [[relatedness]] between the sisterhood of worker bees in a hive or nest is 0.75. This means the workers are significantly more closely related than siblings in other sex determination systems.<ref>The relatedness of siblings in most other systems is 0.5.</ref> It is this point which drives the [[kin selection]] theory of how [[eusociality]] evolved.<ref name=Grimaldi/><sup>p465</sup><ref name=Hamilton>Hamilton W.D. 1964. The genetical evolution of social behaviour, I and II. ''Journal of Theoretical Biology'' '''7''', 1–52. Reprinted with comments in Hamilton W.D. 1996. ''Narrow roads of geneland'', volume I ''Evolution of social behaviour''. Freeman/Spektrum, Oxford. {{ISBN|0