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Encyclopedia > Sex determination

A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most common sex-determination systems in animals involve a genetic mechanism based on the chromosomes of that organism. However, other systems can involve other variables such as temperature. The details of some sex-determination systems are not yet fully understood. Main articles: Life All organisms (viruses not included) consist of cells, which in turn, are based on a common carbon-based biochemistry. ... Look up Sex in Wiktionary, the free dictionary A sex is one of two specimen categories of species that recombine their genetic material in order to reproduce, a process called genetic recombination. ... In biology and ecology, an organism (in Greek organon = instrument) is an assembly of molecules that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... Look up Sex in Wiktionary, the free dictionary A sex is one of two specimen categories of species that recombine their genetic material in order to reproduce, a process called genetic recombination. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Subregnum Bilateria  Acoelomorpha  Orthonectida  Rhombozoa  Myxozoa  Superphylum Deuterostomia     Chordata (vertebrates, etc. ... Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ... Figure 1: Chromosome. ... In biology and ecology, an organism (in Greek organon = instrument) is an assembly of molecules that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... Look up Sex in Wiktionary, the free dictionary A sex is one of two specimen categories of species that recombine their genetic material in order to reproduce, a process called genetic recombination. ...

Contents


Mammals

The most familiar sex-determination system is the XY sex-determination system found in human beings and most other mammals. See the XY sex-determination system article for a detailed discussion of this system. The XY sex-determination system is a well-known sex-determination system. ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals characterized by the presence of mammary glands... The XY sex-determination system is a well-known sex-determination system. ...


Other gene-based systems

The WZ sex-determination system is found in birds and some insects and other organisms. In the WZ sex-determination system, the situation is reversed: females have two different kinds of chromosomes (WZ), and males have two of the same kind of chromosomes (ZZ). Orders Many - see section below. ... Classes & Orders Subclass: Apterygota Orders Archaeognatha (Bristletails) Thysanura (Silverfish) Monura - extinct Subclass: Pterygota Orders Ephemeroptera (mayflies) Odonata (dragonflies and damselflies) Diaphanopteroidea - extinct Palaeodictyoptera - extinct Megasecoptera - extinct Archodonata - extinct Infraclass: Neoptera Orders Blattodea (cockroaches) Isoptera (termites) Mantodea (mantids) Dermaptera (earwigs) Plecoptera (stoneflies) Orthoptera (grasshoppers, etc) Phasmatodea (walking sticks) Embioptera (webspinners) Zoraptera... In biology and ecology, an organism (in Greek organon = instrument) is a living being. ... This article is about the biological chromosome. ... This article is about the biological chromosome. ...


Until recently, it was thought that the WZ system was unrelated to the XY system common to most mammals. A paper published in 2004 (Frank Grützner et al, Nature; doi:10.1038/nature03021) suggests that the two systems may be related. It would seem that platypuses have a ten-chromosome–based system, where the chromosomes form a multivalent chain in male meiosis, segregating into XXXXX-sperm and YYYYY-sperm, with XY-equivalent chromosomes at one end of this chain and the WZ-equivalent chromosomes at the other end. 2004 is a leap year starting on Thursday of the Gregorian calendar. ... Nature is one of the oldest and most reputable general-purpose scientific journals, first published on November 4, 1869. ... Binomial name Ornithorhynchus anatinus (Shaw, 1799) The platypus (Ornithorhynchus anatinus) is a small, half-aquatic mammal endemic to the eastern part of Australia, and one of the four extant monotremes, the only mammals that lay eggs instead of giving birth to live young (the other three are echidnas). ... Figure 1: Chromosome. ... In biology, meiosis is the process that transforms one diploid cell into four haploid cells. ...


Haplodiploidy is found in Hymenoptera. Males are haploid; females are diploid. Thus, if a queen bee mates with one drone, her daughters share 3/4 of their genes with each other, not 1/2 as in the XY and WZ systems. This is believed to be significant for the development of eusociality, as it increases the significance of kin selection. A haplodiploid species is one in which one of the sexes has haploid cells (cells containing one copy of each chromosome) and the other has diploid cells (cells containing two copies of each chromosome). ... Suborders Apocrita Symphyta Many families, see article Hymenoptera is one of the larger orders of Insects, comprising the sawflies, wasps, bees, and ants. ... Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... Families Andrenidae Apidae Colletidae Halictidae Heterogynaidae Megachilidae Melittidae Oxaeidae Sphecidae Stenotritidae bee or bees, see bee (disambiguation). ... Eusociality is the phenomenon of reproductive specialisation found in some species of animal. ... Kin selection was first suggested by Darwin as an explanation of the sterile castes of social insects and has later been mathematically defined by W. D. Hamilton as a mechanism for the evolution of apparently altruistic acts. ...


Other sex-determination systems

Many other exotic sex-determination systems exist. In some species of reptiles, including alligators, sex is determined by the temperature at which the egg is incubated. Other species, such as some snails, practice sex change: adults start out male, then become female. Species Alligator mississippiensis Alligator sinensis Alligator is a genus of the Alligatoridae family of crocodile-like reptiles. ... Giant African Snail (Achatina fulica) The name snail applies to most members of the molluscan class Gastropoda that have coiled shells. ...


Some species have no sex-determination system. Earthworms and some snails are hermaphrodites; a few species of lizard, fish, and insect are all female and reproduce by parthenogenesis. Earthworm is the common reference for the larger members of the Oligochaeta (which is either a class or subclass depending on the author) in the phylum Annelida. ... The 1st-century BC sculpture The Reclining Hermaphrodite, in the Museo Palazzo Massimo Alle Terme in Rome In zoology, a hermaphrodite is an organism of a species whose members possess both male and female sexual organs during their lives. ... Kaguya is one success from 460 attempts at growing embryos. ...


In some arthropods, sex is determined by infection. Bacteria of the genus Wolbachia alter their sexuality; some species consist entirely of ZZ individuals, with sex determined by the presence of Wolbachia. Subphyla and Classes Subphylum Trilobitomorpha Trilobita - Trilobites (extinct) Subphylum Chelicerata Arachnida - Spiders, Scorpions, etc. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Wolbachia is a type of bacteria that infects arthropod species, including a high proportion of all insects. ...


Other unusual systems [this section still being researched]:

Binomial name Xiphophorus hellerii Heckel, 1848 The green swordtail (Xiphophorus hellerii) is a species of freshwater fish in family Poecilidae of order Cyprinodontiformes. ...

See also

Testis-determining factor is a general term for the gene (or product thereof) that results in maleness in humans and some other species. ... In those species in which sex is determined by the presence of the Y or W chromosome rather than the diploidy of the X or Z, a Barr body is the inactive X chromosome in a female cell, or the inactive Z in a male. ... Protandry is a form of sequential hermaphroditism where organisms begin as males and then change into females. ... A sex organ, or primary sexual characteristic, narrowly defined, is any of those parts of the body (which are not always bodily organs according to the strict definition) which are involved in sexual reproduction and constitute the reproductive system in a complex organism; namely: Male: penis (notably the glans penis... Secondary sex characteristics are traits that distinguish the two sexes of a species, but that are not directly part of the reproductive system. ...

External links

  • The Unusual Sex Determination System of Chironomus
  • The Enigma of Sex Determination in Reptiles
  • Nature news article about duck-billed platypus sex determination

Reference

  • (2004) Evolution of Sex Chromosomes: The Case of the White Campion. PLoS Biol 3(1): e28.

  Results from FactBites:
 
Sex determination in Hymenoptera (4726 words)
In addition to unique selective pressures governing sex determination in some Hymenoptera, analyses of the evolution of sex determination in the order are hindered by the fact that in many cases, the actual Hymenopteran being studied is not the only organism with a vested interest in determining its sex.
A second peculiarity in Hymenopteran sex determination is the existence, in at least one species, of a so-called selfish chromosome which is inherited at greater than Mendelian proportion.
Skinner, S.W. and Werren, J.H. The genetics of sex determination in Nasonia vitripennis (Hymenoptera: Pteromalidae).
  More results at FactBites »

 
 

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