Editing Hymenoptera (section)

===Sex determination===
{{main|Haplodiploid sex-determination system}}

Among most or all hymenopterans, sex is [[sex-determination system|determined]] by the number of [[chromosome]]s an individual possesses.<ref name=Cowan2004>{{cite journal |last1=Cowan |first1=David P. Cowan |last2=Stahlhut |first2=Julie K. | title=Functionally reproductive diploid and haploid males in an inbreeding hymenopteran with complementary sex determination | journal=PNAS | volume=101 | issue=28 | pages=10374–10379 | date=13 July 2004 | doi=10.1073/pnas.0402481101 | pmid=15232002 | pmc=478579 |bibcode=2004PNAS..10110374C|doi-access=free }}</ref> Fertilized eggs get two sets of chromosomes (one from each parent's respective [[gamete]]s) and develop into [[diploid]] females, while unfertilized eggs only contain one set (from the mother) and develop into [[haploid]] males. The act of fertilization is under the voluntary control of the egg-laying female, giving her control of the sex of her offspring.<ref name=IIBD/> This phenomenon is called [[haplodiploidy]].

However, the actual genetic mechanisms of haplodiploid sex determination may be more complex than simple chromosome number. In many Hymenoptera, sex is determined by a single gene locus with many alleles.<ref name=Cowan2004/> In these species, haploids are male and diploids heterozygous at the sex locus are female, but occasionally a diploid will be homozygous at the sex locus and develop as a male, instead. This is especially likely to occur in an individual whose parents were [[siblings]] or other close relatives. Diploid males are known to be produced by inbreeding in many ant, bee, and wasp species. Diploid biparental males are usually sterile but a few species that have fertile diploid males are known.<ref>{{Cite journal | last1=Elias | first1=J. | last2=Mazzi | first2=D. | last3=Dorn | first3=S. | editor1-last=Bilde | editor1-first=Trine | title=No Need to Discriminate? Reproductive Diploid Males in a Parasitoid with Complementary Sex Determination | doi=10.1371/journal.pone.0006024 | journal=PLOS ONE | volume=4 | issue=6 | pages=e6024 | year=2009 | pmid=19551142| pmc =2696080 | bibcode=2009PLoSO...4.6024E| doi-access=free }}</ref>

One consequence of haplodiploidy is that females on average have more genes in common with their sisters than they do with their daughters. Because of this, cooperation among kindred females may be unusually advantageous and has been hypothesized to contribute to the multiple origins of [[eusociality]] within this order.<ref name=IIBD/><ref>{{Cite journal |last1=Quiñones |first1=Andrés E. |last2=Pen |first2=Ido |date=June 2017 |title=A unified model of Hymenopteran preadaptations that trigger the evolutionary transition to eusociality |journal=Nature Communications |volume=8 |pages=15920 |doi=10.1038/ncomms15920 |pmc=5490048 |pmid=28643786|bibcode=2017NatCo...815920Q}}</ref> In many colonies of bees, ants, and wasps, worker females will remove eggs laid by other workers due to increased relatedness to direct siblings, a phenomenon known as [[worker policing]].<ref>Davies, N.R.; Krebs, J.R.; and West, S.A. An Introduction to Behavioral Ecology. 4th ed. West Sussex: Wiley-Blackwell, 2012. pp. 387–388</ref>

Another consequence is that hymenopterans may be more resistant to the deleterious effects of [[Inbreeding depression|inbreeding]]. As males are haploid, any recessive genes will automatically be expressed, exposing them to natural selection. Thus, the [[genetic load]] of deleterious genes is purged relatively quickly.<ref>{{Cite book |title=Hymenoptera and biodiversity |first1=John |last1=LaSalle |last2=David |first2=Gauld, Ian |date=1993 |publisher=C.A.B. International |isbn=978-0851988306 |oclc=28576921 }}</ref>