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Thelytoky comes from the Greek thely, meaning "female", and tok, meaning "birth". Thelytokous parthenogenesis is a type of parthenogenesis in which females are produced from unfertilized eggs. It is rare in the animal kingdom and has only been reported in about 1500 species.[1] It is more common in invertebrates, like arthropods, but can also occur in vertebrates, like some whiptail lizards. Hymenoptera (ants, bees and wasps) for example, are haplodiploid and usually reproduce by arrhenotokous parthenogenesis, in which unfertilized eggs develop into haploid males, and fertilized eggs develop into diploid females but thelytoky has been described in several taxa, including Cynipidae, Tenthredinidae, Aphelinidae, Ichneumonidae, Apidae and Formicidae.[2] It can also be induced in Hymenoptera by the bacteria Wolbachia and Cardinium.[3]

Thelytoky can occur by a number of different mechanisms each of which has a different impact on the level of inbreeding.

An example of thelytoky is the reproduction of female workers or queens by laying worker bees. It occurs in the Cape bee, Apis mellifera capensis and has been found in other strains at very low frequency. In honey bees, thelytoky occurs when diploidy is restored by the fusion of two meiotic products.[4] Usually, unfertilized eggs are haploid containing only a single set of chromosomes (16) from the mother. Cape bee laying workers are capable of laying unfertilized diploid (32 chromosomes) eggs. These eggs undergo an unusual biological life cycle. A late stage of meiosis is anaphase when the chromosomes separate. In parthenogenesis (the reproduction without male fertilization), anaphase is followed by fusion of two meiotic products to restore diploidy (the egg pronucleus and the central descendant of the first polar body fuse to form a zygote with a diploid nucleus). The zygote develops into an embryo. Depending on how the embryo is fed it can develop into a worker bee or a queen bee.

References

  1. ^ White M (1984). Chromosomal mechanisms in animal reproduction. Bull Zool 51: 1–23.
  2. ^ Suomalainen E, Saura A, Lokki J (1987). Cytology and Evolution in Parthenogenesis. CRC Press Inc.: Boca Raton, FL.
  3. ^ G. Jeong and Stouthamer, R. (2005) Genetics of female functional virginity in the Parthenogenesis-Wolbachia infected parasitoid wasp Telenomus nawai (Hymenoptera: Scelionidae). Heredity 94:402-407
  4. ^ E. Baudry et al. (2004) Whole-Genome Scan in Thelytokous-Laying Workers of the Cape Honey bee (Apis mellifera capensis): Central Fusion, Reduced Recombination Rates and Centromere Mapping Using Half-Tetrad Analysis. Genetics 167:243-252

See also


Thelytoky comes from the Greek thely, meaning "female", and tok, meaning "birth". Thelytokous parthenogenesis is a type of parthenogenesis in which females are produced from unfertilized eggs. It is rare in the animal kingdom and has only been reported in about 1500 species.[1] It is more common in invertebrates, like arthropods, but can also occur in vertebrates, like some whiptail lizards. Thelytoky can occur by a number of different mechanisms each of which has a different impact on the level of homozygosity. It can be induced in Hymenoptera by the bacteria Wolbachia and Cardinium[2], and has also been described in several groups of Hymenoptera, including Cynipidae, Tenthredinidae, Aphelinidae, Ichneumonidae, Apidae and Formicidae.[3]

Hymenoptera (ants, bees and wasps) usually reproduce by arrhenotokous parthenogenesis. They have the haplodiploid sex-determination system, and usually unfertilized eggs develop into haploid males, and fertilized eggs develop into diploid females. In thelytoky, however, female workers or queens are produced by laying worker bees when diploidy is restored in their eggs by the fusion of two meiotic products.[4]. These laying workers are therefore producing unfertilized diploid eggs (with the full complement of 32 chromosomes). It occurs in the Cape bee, Apis mellifera capensis, a strain of honey bee, and has been found in other strains at very low frequency. The diploid embryo that develops from the egg can develop into a worker bee or a queen bee depending on how it is fed.[clarification needed]

References

  1. ^ White M (1984). Chromosomal mechanisms in animal reproduction. Bull Zool 51: 1–23.
  2. ^ G. Jeong and Stouthamer, R. (2005) Genetics of female functional virginity in the Parthenogenesis-Wolbachia infected parasitoid wasp Telenomus nawai (Hymenoptera: Scelionidae). Heredity 94:402-407
  3. ^ Suomalainen E, Saura A, Lokki J (1987). Cytology and Evolution in Parthenogenesis. CRC Press Inc.: Boca Raton, FL.
  4. ^ E. Baudry et al. (2004) Whole-Genome Scan in Thelytokous-Laying Workers of the Cape Honey bee (Apis mellifera capensis): Central Fusion, Reduced Recombination Rates and Centromere Mapping Using Half-Tetrad Analysis. Genetics 167:243-252

See also


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