As haplodiploidy refers to a form of Geschlechtsdetermination in which a sex only one set of chromosomes carrying ( haploid ) and the opposite sex of the double set of chromosomes ( diploid ). Usually the male sex is haploid.
One can differentiate between two basic types of haplodiploidy depending on the origin:
- Arrhenotocia - haploid individuals arise through parthenogenesis , i.e. from an unfertilized egg cell
- Pseudoarrhenotokia - haploid individuals due to subsequent loss of the paternal genome
In over 2000 species of hymenoptera ( ants , bees , wasps, etc.), males hatch from unfertilized eggs and are therefore haploid . Haplodiploidy is also found in some bark beetles ( tribe Xyloborini and kinship circle of the genus Coccotrypes in the tribe Dryocoetini ), many thrips , some scale insects , mites and nematode group Oxyuroidea .
Since the genome of the males can also be found in the mother and in the female siblings and is thus extremely related, it is assumed that haplodiploidy favors the formation of states . On the other hand, sex determination in termites does not take place haplodiploid, nevertheless highly developed forms of social organization have developed in all species of this hemimetabolic insect order.
In the case of the well-examined bees, it has been found that, similar to humans, a certain gene is ultimately decisive for determining sex. If it is available in two different versions (in the case of the fertilized eggs), females arise. If there is only one version (in the case of unfertilized eggs), males result. By inbreeding can to come that this gene is present in fertilized eggs in two identical versions. Then diploid males emerge. However, their larvae are eaten by the workers after they hatch from the egg.
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