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W Chromosome
The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), the schistosome family of flatworms, and some reptiles, e.g. majority of snakes, lacertid lizards and monitors including Komodo dragons. It is also used in some plants where it has probably evolved independently on several occasions. The letters Z and W are used to distinguish this system from the XY sex-determination system. In this system, females have a pair of dissimilar ZW chromosomes, and males have two similar ZZ chromosomes. In contrast to the XY sex-determination system and the X0 sex-determination system, where the sperm determines the sex, in the ZW system, the ovum determines the sex of the offspring. Males are the homogametic sex (ZZ), while females are the heterogametic sex (ZW). The Z chromosome is larger and has more genes, like the X chromosome in the XY ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Avian Sex Determination , a virus adapted to birds
* Evian, a brand of mineral water
* Évian-les-Bains, a commune in eastern France
* Avian may refer to: *Birds or Aves, winged animals *Avian (given name) (russian: Авиа́н, link=no), a male forename Aviation * Avro Avian, a series of light aircraft made by Avro in the 1920s and 1930s * Avian Limited, a hang glider manufacturer founded in 1989 Places *Avian, Iran *Aviano ( fur, Avian, link=no), northern Italy *Avian Island, Antarctica See also *Avian influenza Avian influenza, known informally as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Common Ancestor
Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal common ancestor (LUCA) of all life on Earth, according to modern evolutionary biology. Common descent is an effect of speciation, in which multiple species derive from a single ancestral population. The more recent the ancestral population two species have in common, the more closely are they related. The most recent common ancestor of all currently living organisms is the last universal ancestor, which lived about 3.9 billion years ago. The two earliest pieces of evidence for life on Earth are graphite found to be biogenic in 3.7 billion-year-old metasedimentary rocks discovered in western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. All currently living organisms on Earth sha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parthenogenesis
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development of embryos occur in a gamete (egg or sperm) without combining with another gamete (e.g., egg and sperm fusing). In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plants, parthenogenesis is a component process of apomixis. In algae, parthenogenesis can mean the development of an embryo from either an individual sperm or an individual egg. Parthenogenesis occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea and parasitic wasps) and a few vertebrates (such as some fish, amphibians, reptiles and birds). This type of reproduction has been induced artificially i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pythonoidea
The Pythonoidea, also known as pythonoid snakes, are a superfamily of snakes that contains pythons (family Pythonidae) and other closely related python-like snakes (but not boas, which are in a separate superfamily called Booidea). As of 2022, Pythonoidea contains 39 species, including the eponymous genus ''Python'' and 10 other genera of pythons ('' Antaresia'', '' Apodora'', '' Aspidites'', '' Bothrochilus'', '' Leiopython'', ''Liasis'', '' Malayopython'', ''Morelia'', '' Nyctophilopthon'' and '' Simalia''), all in the family Pythonidae, as well as two lesser-known families, Loxocemidae (one species, the Mexican burrowing python, in the genus '' Loxocemus'') and Xenopeltidae (two species of sunbeam snakes in the genus '' Xenopeltis''). The taxonomy of pythons, boas, and other henophidian snakes has long been debated, and ultimately the decision whether to assign a particular clade to a particular Linnaean rank (such as a superfamily, family Family (from la, familia) is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Booidea
The Booidea, also known as booid snakes, are a superfamily of snakes that contains boas (family Boidae) and other closely related boa-like snakes (but not pythons, which are in a separate superfamily called Pythonoidea). As of 2017, Booidea contains 61 species, including the eponymous neotropical ''Boa constrictor'', anacondas (genus '' Eunectes''), and smaller tree and rainbow boas ('' Corallus'', '' Epicrates'', and ''Chilabothrus'') as well as several genera of booid snakes from various locations around the world: bevel-nosed boas or keel-scaled boas ('' Candoia'') from New Guinea and Melanesia, Old World sand boas ('' Eryx'') from Northeast Africa, the Middle East, and Southwest Asia, rubber boas (''Charina'') and rosy boas ('' Lichanura'') from North America, neotropical dwarf boas ('' Ungaliophis'') and the Oaxacan dwarf boa ('' Exiliboa'') from Central America, Madagascan boas or Malagasy boas ('' Acrantophis'' and '' Sanzinia'') from Madagascar, and the Calabar python (''Ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sex-link
Sex-links are crossbred chickens whose color at hatching is differentiated by sex, thus making chick sexing an easier process. Sex-links come in several varieties. As hybrids of laying or dual-purpose breeds infused with extra vigor via heterosis, sex-links can be extremely good egg-layers which often produce 300 eggs a year or more depending on the quality of care and feed. The color of their eggs vary according to the mix of breeds, and blue-green eggs are possible. Chicks of a single breed that are similarly sex-linked are called autosex chickens, a term developed to differentiate between sex linkage in purebred chickens versus sex linkage in crossbreeds. Sex-link types Many common varieties are known as the black sex-link (also called black stars) and the red sex-link (also called red stars). More specific variety names are common as well. * Black sex-link like "Black rocks" are a cross between unique specially bred hybrid strains of Rhode Island Red rooster (but any n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DMRT1
Doublesex and mab-3 related transcription factor 1, also known as DMRT1, is a protein which in humans is encoded by the ''DMRT1'' gene. Function DMRT1 is a dose sensitive transcription factor protein that regulates Sertoli cells and germ cells. The DMRT1 gene is located at the end of the 9th chromosome. This gene is found in a cluster with two other members of the gene family, having in common a zinc finger-like DNA-binding motif (DM domain). The DM domain is an ancient, conserved component of the vertebrate sex-determining pathway that is also a key regulator of male development in flies and nematodes, and is found to be the key sex-determining factor in chickens. The majority of DMRT1 protein is located in the testicular cord and Sertoli cells, with a small amount in the germ cells. This gene exhibits a gonad-specific and sexually dimorphic expression pattern, just like the related ''doublesex'' gene in fruit flies. Defective testicular development and XY feminization occur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell. The resulting fusion of these two cells produces a single-celled zygote that undergoes many cell divisions that produce cells known as blastomeres. The blastomeres are arranged as a solid ball that when reaching a certain size, called a morula, takes in fluid to create a cavity called a blastocoel. The structure is then termed a blastula, or a blastocyst in mammals. The mammalian blastocyst hatches before implantating into the endometrial lining of the womb. Once implanted the embryo will continue its development through the next stages of gastrulation, neurulation, and organogenesis. Gastrulation is the formation of the three germ layers that will form all of the different parts of the body. Neurulation forms the ner ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dosage Compensation
Dosage compensation is the process by which organisms equalize the expression of genes between members of different biological sexes. Across species, different sexes are often characterized by different types and numbers of sex chromosomes. In order to neutralize the large difference in gene dosage produced by differing numbers of sex chromosomes among the sexes, various evolutionary branches have acquired various methods to equalize gene expression among the sexes. Because sex chromosomes contain different numbers of genes, different species of organisms have developed different mechanisms to cope with this inequality. Replicating the actual ''gene'' is impossible; thus organisms instead equalize the ''expression'' from each gene. For example, in humans, females (XX) silence the transcription of one X chromosome of each pair, and transcribe all information from the other, expressed X chromosome. Thus, human females have the same number of expressed X-linked genes as do human males ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dosage Compensation
Dosage compensation is the process by which organisms equalize the expression of genes between members of different biological sexes. Across species, different sexes are often characterized by different types and numbers of sex chromosomes. In order to neutralize the large difference in gene dosage produced by differing numbers of sex chromosomes among the sexes, various evolutionary branches have acquired various methods to equalize gene expression among the sexes. Because sex chromosomes contain different numbers of genes, different species of organisms have developed different mechanisms to cope with this inequality. Replicating the actual ''gene'' is impossible; thus organisms instead equalize the ''expression'' from each gene. For example, in humans, females (XX) silence the transcription of one X chromosome of each pair, and transcribe all information from the other, expressed X chromosome. Thus, human females have the same number of expressed X-linked genes as do human males ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Therian Mammals
Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes. Characteristics Therian mammals give birth (''see viviparity'') to live young without a shelled egg. This is possible thanks to key proteins called syncytins which allow exchanges between the mother and its offspring through a placenta, even rudimental ones such as in marsupials. Genetic studies have suggested a viral origin of syncytins through the endogenization process. The marsupials and the placental mammals evolved from a common therian ancestor that gave live birth by suppressing the mother's immune system. While the marsupials continued to give birth to an underdeveloped fetus after a short pregnancy, the ancestors of placental mammals gradually evolved a prolonged pregnancy. Therian mammals no longer have the coracoid bone ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theria
Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes. Characteristics Therian mammals give birth (''see viviparity'') to live young without a shelled egg. This is possible thanks to key proteins called syncytins which allow exchanges between the mother and its offspring through a placenta, even rudimental ones such as in marsupials. Genetic studies have suggested a viral origin of syncytins through the endogenization process. The marsupials and the placental mammals evolved from a common therian ancestor that gave live birth by suppressing the mother's immune system. While the marsupials continued to give birth to an underdeveloped fetus after a short pregnancy, the ancestors of placental mammals gradually evolved a prolonged pregnancy. Therian mammals no longer have the coracoid bone ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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