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Encyclopedia > Sex determination system

A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most sexual organisms have two sexes. In many cases, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual morphology. In animals, this is often accompanied by chromosomal differences. In other cases, sex is determined by environmental variables (such as temperature) or social variables (the size of an organism relative to other members of its population). The details of some sex-determination systems are not yet fully understood. Biology (from Greek βίος λόγος, see below) is the branch of science dealing with the study of living organisms. ... Look up Sex in Wiktionary, the free dictionary. ... A crab is an example of an organism. ... Look up Sex in Wiktionary, the free dictionary. ... The shield and spear of the Roman God Mars are often used to represent the male sex In heterogamous species, male is the sex of an organism, or of a part of an organism, which typically produces smaller, mobile gametes (spermatozoa) that are able to fertilise female gametes (ova). ... The hand mirror and comb of the Roman Goddess Venus is often used to represent the female sex. ... An allele is any one of a number of viable DNA codings occupying a given locus (position) on a chromosome. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... Comparative anatomy is the study of similarities and differences in the anatomy of organisms. ... Phyla Placozoa (trichoplax) Orthonectida (orthonectids) Rhombozoa (dicyemids) Subregnum Parazoa Porifera (sponges) Subregnum Eumetazoa Radiata (unranked) (radial symmetry) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Bilateria (unranked) (bilateral symmetry) Acoelomorpha (basal) Myxozoa (slime animals) Superphylum Deuterostomia (blastopore becomes anus) Chordata (vertebrates, etc. ... Figure 1: Chromosome. ... An ecosystem, a contraction of ecological and system, refers to the collection of components and processes that comprise, and govern the behavior of, some defined subset of the biosphere. ... Fig. ... A crab is an example of an organism. ...


Chromosomal determination

XX/XY sex chromosomes

The XX/XY sex-determination system is one of the most familiar sex-determination systems and is found in human beings and most other mammals. In the XY sex-determination system, females have two of the same kind of sex chromosome (XX), while males have two distinct sex chromosomes (XY). Some species (including humans) have a gene SRY on the Y chromosome that determines maleness; others (such as the fruit fly) use the presence of two X chromosomes to determine femaleness. The XY sex-determination system is a well-known sex-determination system. ... Trinomial name Homo sapiens sapiens Linnaeus, 1758 Humans, or human beings, are bipedal primates belonging to the mammalian species Homo sapiens (Latin for wise man or knowing man) under the family Hominidae (known as the great apes). ... Orders Multituberculata (extinct) Palaeoryctoides (extinct) Triconodonta (extinct) Subclass Australosphenida Ausktribosphenida Monotremata Subclass Eutheria (excludes extinct ancestors) Afrosoricida Anagaloidea (extinct) Arctostylopida (extinct) Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Cingulata Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Dinocerata (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Leptictida (extinct) Litopterna (extinct) Macroscelidea Mesonychia (extinct) Notoungulata... Figure 1: Chromosome. ... SRY (Sex-determining Region Y) is a sex-determining gene on the Y chromosome in humans and other primates. ... Binomial name Drosophila melanogaster Meigen, 1830 Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a dipteran (two-winged) insect, and is the species of fruit fly that is most commonly used in genetic experiments; it is among the most important model organisms. ...

XX/X0 sex determination

Main article: X0 sex-determination system

In this variant of the XY system, females have two copies of the sex chromosome (XX) but males have only one (X0). The 0 denotes the absence of a second sex chromosome. This system is observed in a number of insects, including the grasshoppers and crickets of order Orthoptera and in cockroaches (order Blattodea). The X0 sex-determination system is a system that grasshoppers, crickets, roaches, and some other insects use to determine the sex of their offspring. ... Classes & Orders See taxonomy Insects are invertebrate animals of the Class Insecta, the largest and (on land) most widely-distributed taxon within the phylum Arthropoda. ... Suborders and families Suborder Ensifera - crickets Superfamily Gryllacroidea Gryllacrididae - camel crikets Rhaphidophoridae - cave crickets Schizodactylidae - dune crickets Stenopelmatidae - king crickets Superfamily Grylloidea Gryllidae - true crickets Gryllotalpidae - mole cricket Mogoplistidae Myrmecophilidae Superfamily Tettigonioidea Anostostomatidae - king crickets Bradyporidae - armoured crickets Haglidae Phaneropteridae Tettigoniidae - katydids, koringkrieks Suborder Caelifera - grasshoppers, locusts Superfamily Acridoidea Acrididae... Families Blaberidae Blattellidae Blattidae Cryptocercidae Polyphagidae Nocticolidae Cockroaches are insects of the Order Blattodea. ...

The nematode C. elegans is male with one sex chromosome (X0); with a pair of chromosomes (XX) it is a hermaphrodite. Classes Adenophorea    Subclass Enoplia    Subclass Chromadoria Secernentea    Subclass Rhabditia    Subclass Spiruria    Subclass Diplogasteria The nematodes or roundworms (Phylum Nematoda from Gr. ... Binomial name Caenorhabditis elegans Maupas, 1900 Caenorhabditis elegans (pronounced see-no-rab-DYE-tis) is a free-living nematode (one of the roundworms), about 1 mm in length, which lives in a temperate soil environment. ... The 1st-century BC sculpture The Reclining Hermaphrodite, in the Museo Nazionale Romano, Palazzo Massimo Alle Terme in Rome In zoology and botany, a hermaphrodite aka Sean Daly is an organism that possesses both male and female sex organs during its life[1]. In many species, hermaphroditism is a common...

ZW sex chromosomes

Main article: ZW sex-determination system

The ZW sex-determination system is found in birds and some insects and other organisms. The ZW sex-determination system is reversed compared to the XY system: females have two different kinds of chromosomes (ZW), and males have two of the same kind of chromosomes (ZZ). The ZW sex-determination system is a system that birds, some fishes, and some insects (including butterflies and moths) use to determine the sex of their offspring. ... Orders Many - see section below. ... Classes & Orders See taxonomy Insects are invertebrate animals of the Class Insecta, the largest and (on land) most widely-distributed taxon within the phylum Arthropoda. ... A crab is an example of an organism. ... This article is about the biological chromosome. ... This article is about the biological chromosome. ...

It is unknown whether the presence of the W chromosome induces female features or the duplication of the Z chromosome induces male ones; unlike mammals, no birds with a double W chromosome (ZWW) or a single Z (Z0) have been discovered. Probably that either condition causes embryonic death, and both chromosomes are responsible for gender selection.

In Lepidoptera, examples of Z0, ZZW and ZZWW females can be found. This suggests that the W chromosome is essential in female determination in some species (ZZW), but not in others (Z0). In Bombyx mori (the commercial silkworm), the W chromosome carries the female-determining genes. Super Families Butterflies Hesperioidea Papilionoidea Moths Micropterigoidea Heterobathmioidea Eriocranioidea Acanthopteroctetoidea Lophocoronoidea Neopseustoidea Mnesarchaeoidea Hepialoidea Nepticuloidea Incurvarioidea Palaephatoidea Tischeriodea Simaethistoidea Tineoidea Gracillarioidea Yponomeutoidea Gelechioidea Zygaenoidea Sesioidea Cossoidea Tortricoidea Choreutoida Urodoidea Galacticoidea Schreckensteinioidea Epermenioidea Pterophoroidea Aluctoidea Immoidea Axioidea Hyblaeoidea Thyridoidea Whalleyanoidea Pyraloidea Mimallonoidea Lasiocampoidea Geometroidea Drepanoidea Bombycoidea Calliduloidae Hedyloidea Noctuoidea Families About... Binomial name Bombyx mori Linnaeus, 1758 For the band named Silkworm, see Silkworm (band). ...

Chromosomes in the ZW region in birds are autosomal in mammals, and vice-versa; therefore, it is theorized that the ZW and XY couples come from different chromosomes of the common ancestor. A paper published in 2004 (Frank Grützner et al, Nature; DOI:10.1038/nature03021) suggests that the two systems may be related. According to the paper, 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 ZW-equivalent chromosomes at the other end. An autosome is a non-sex chromosome. ... Missing link is a term for a transitional form from the fossil record that connects an earlier species to a later one, or which connects two different species to an earlier ancestor. ... 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... First title page, November 4, 1869 Nature is one of the oldest and most reputable scientific journals, first published on 4 November 1869. ... A digital object identifier (or DOI) is a permanent identifier (permalink) given to a World Wide Web file or other Internet document so that if its Internet address changes, users will be redirected to its new address. ... Binomial name Ornithorhynchus anatinus (Shaw, 1799) Platypus range (indicated by darker shading)[2] The platypus (Ornithorhynchus anatinus) is a semi-aquatic mammal endemic to eastern Australia and Tasmania. ... Figure 1: Chromosome. ... In biology, meiosis is the process that allows one diploid cell to divide in a special way to generate haploid cells in eukaryotes. ...


Main article: Ploidy
Main article: Haplo-diploid sex-determination system

Haplodiploidy is found in insects belonging to Hymenoptera, such as ants and bees. Haploid individuals are male. Diploid individuals are generally female but may be sterile males. Thus, if a queen bee mates with one drone, her daughters share ¾ of their genes with each other, not ½ as in the XY and ZW systems. This is believed to be significant for the development of eusociality, as it increases the significance of kin selection. Ploidy is the number of sets of homologous chromosomes in a cell. ... The Haplo-diploid sex-determination system is a system that most species of bees and ants use to determine the sex of their offspring. ... Ploidy is the number of sets of homologous chromosomes in a cell. ... Orders Subclass Apterygota Symphypleona - globular springtails Subclass Archaeognatha (jumping bristletails) Subclass Dicondylia Monura - extinct Thysanura (common bristletails) Subclass Pterygota Diaphanopteroidea - extinct Palaeodictyoptera - extinct Megasecoptera - extinct Archodonata - extinct Ephemeroptera (mayflies) Odonata (dragonflies and damselflies) Infraclass Neoptera Blattodea (cockroaches) Mantodea (mantids) Isoptera (termites) Zoraptera Grylloblattodea Dermaptera (earwigs) Plecoptera (stoneflies) Orthoptera (grasshoppers, crickets... Suborders Apocrita Symphyta Many families, see article Hymenoptera is one of the larger orders of Insects, comprising the sawflies, wasps, bees, and ants. ... Subfamilies Aenictinae Aenictogitoninae Aneuretinae Apomyrminae Cerapachyinae Dolichoderinae Dorylinae Ecitoninae Formicinae Leptanillinae Leptanilloidinae Myrmeciinae Myrmicinae Nothomyrmeciinae Ponerinae Pseudomyrmecinae Diagram of a worker ant (Pachycondyla verenae). ... Families Andrenidae Apidae Colletidae Halictidae Megachilidae Melittidae Stenotritidae Bee collecting pollen Bees (a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila) are flying insects, closely related to wasps 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 Megachilidae Melittidae Stenotritidae Bee collecting pollen Bees (a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila) are flying insects, closely related to wasps and ants. ... This section does not cite its references or sources. ... Kin selection refers to changes in gene frequency across generations that are driven at least in part by interactions between related individuals, and this forms much of the conceptual basis of the theory of social evolution. ...

Non-genetic sex-determination systems

Many other exotic sex-determination systems exist. In some species of reptiles, including alligators and the tuatara, 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. In tropical clown fish, the dominant individual in a group becomes female while the other ones are male. Species Alligator mississippiensis Alligator sinensis An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. ... Species Sphenodon punctatus (Gray, 1842) Sphenodon guntheri Buller, 1877 Sphenodon diversum (extinct) The tuatara is a reptile of the family Sphenodontidae, endemic to New Zealand. ... The name snail applies to most members of the molluscan class Gastropoda that have coiled shells. ... Species Twenty-seven, including: Amphiprion allardi - Allards Clownfish Amphiprion melanopus - Cinnamon Clownfish Amphiprion clarkii - Clarks Anemonefish Amphiprion ocellaris - Ocellaris Clownfish Amphiprion percula - Percula Clownfish Amphiprion perideraion - Pink Skunk Clownfish Amphiprion polymnus - Saddleback Clownfish Amphiprion sebae - Sebae Clownfish Amphiprion tricinctus - Three-Band Anemonefish Amphiprion ephippium - Tomato Clownfish Amphiprion frenatus...

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. Families   Acanthodriladae   Ailoscolecidae   Alluroididae   Almidae   Biwadrilidae   Eudrilidae   Exxidae   Glossoscolecidae   Lumbricidae   Lutodrilidae   Megascolecidae   Microchaetidae   Ocnerodrilidae   Octochaetidae   Sparganophilidae Earthworm is the common name 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 Nazionale Romano, Palazzo Massimo Alle Terme in Rome In zoology and botany, a hermaphrodite aka Sean Daly is an organism that possesses both male and female sex organs during its life[1]. In many species, hermaphroditism is a common... 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 (Lyon, 2003), rendered inactive in... Protandry is a form of sequential hermaphroditism where organisms begin as males and then change into females. ... Wikipedia does not have an article with this exact name. ... A sex organ, or primary sexual characteristic, narrowly defined, is any of those anatomical 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... A peafowl displays its secondary sexual characteristics (long, colored feathers). ... Concept The Shettles Method is a child conception idea that is reputed to help determine a babys sex. ...

External links


  • (2004) Evolution of Sex Chromosomes: The Case of the White Campion.
Evolution of chromosomes
Basic topics: Chromosome | Karyotype | Ploidy | Meiosis
Classification: Autosome | Sex chromosome
Evolution: Chromosomal inversion | Chromosomal translocation | Polyploidy



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