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Sex Reversal
Sex reversal is a biological process whereby the pathway directed towards the already determined-sex fate is flipped towards the opposite sex, creating a discordance between the primary sex fate and the sex phenotype expressed. The process of sex reversal occurs during embryonic development or before gonad differentiation. In GSD species sex reversal means that the sexual phenotype is discordant with the genetic/chromosomal sex. In TSD species sex reversal means that the temperature/conditions that usually trigger the differentiation towards one sexual phenotype are producing the opposite sexual phenotype. Sex reversal can occur naturally, by mutations, or can be induced artificially. Sex reversal can be genetically or hormonally induced in laboratory. It can also occur artificially by exposure to endocrine disruptors such as pollutants, including herbicides, which can act as estrogen promoters or inhibitors, for instance by altering aromatase expression. In vertebrates In go ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sex-determination System
A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two sexes. In some species there are hermaphrodites. There are also some species that are only one sex due to parthenogenesis, the act of a female reproducing without fertilization. In some species, 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, generally through combinations of XY, ZW, XO, ZO chromosomes, or haplodiploidy. The sexual differentiation is generally triggered by a main gene (a "sex locus"), with a multitude of other genes following in a domino effect. In other cases, sex of a fetus is determined by environmental variables (such as temperature). The details of some sex-determination systems are not yet fully underst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cattle
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult males are referred to as bulls. Cattle are commonly raised as livestock for meat (beef or veal, see beef cattle), for milk (see dairy cattle), and for hides, which are used to make leather. They are used as riding animals and draft animals ( oxen or bullocks, which pull carts, plows and other implements). Another product of cattle is their dung, which can be used to create manure or fuel. In some regions, such as parts of India, cattle have significant religious significance. Cattle, mostly small breeds such as the Miniature Zebu, are also kept as pets. Different types of cattle are common to different geographic areas. Taurine cattle are found primarily in Europe and temperate areas of Asia, the Americas, and Australia. Zebus (also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cabrera's Vole
Cabrera's vole (''Microtus cabrerae'') is a species of vole native to Spain and Portugal. It is named for Ángel Cabrera, a mammalogist then working at the Museo Nacional de Ciencias Naturales in Madrid. It is the only living member of the subgenus ''Iberomys'', although two fossil species are also known, including ''M. brecciensis'', the likely direct ancestor of the living species. Description Cabrera's vole is one of the largest voles in the genus ''Microtus'', with a body length of and a tail in length. Adults weigh between , up to five times more than other voles native to Spain and Portugal. They have long, thick fur which is brownish olive over most of the body and yellowish in colour on the underparts. The guard hairs are particularly long, reaching as far as out from the body, greater than that in any other ''Microtus'' species. Internally, the caecum is longer than that in most other voles, relative to body size, a feature that may be related to its specialised diet. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
African Pygmy Mouse
The African pygmy mouse (''Mus minutoides'') is one of the smallest rodents. It is widespread within sub-Saharan Africa, and is kept as a pet in other parts of the world. Like the common house mouse, it is a member of the enormous superfamily Muroidea, which includes about 1000 different species. Grey to brick-red overall, it is pale on the underside and has small but prominent triangular ears. Adults are between long, with a tail, and weigh from . African pygmy mice reach breeding age at about 6 to 8 weeks. Pregnancy lasts for around 20 days and the litter of about three young is born blind and hairless. Their eyes open after 2 weeks, and weaning is complete after 4 weeks. The lifespan is about 2 years, although individual specimens have been reported to live over 4 years in captivity. The African pygmy mouse has a number of unique traits. It stacks pebbles in front of its burrow. Overnight, the pebbles gather dew and in the morning, the pygmy mouse drinks the dew on the pe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Akodon
''Akodon'' is a genus consisting of South American grass mice. They mostly occur south of the Amazon Basin and along the Andes north to Venezuela, but are absent from much of the basin itself, the far south of the continent, and the lowlands west of the Andes. ''Akodon'' is one of the most species-rich genera of Neotropical rodents. Species of ''Akodon'' are known to inhabit a variety of habitats from tropical and tropical moist forests to altiplano and desert. Fossils are known from the late Pliocene onwards. Taxonomy ''Akodon'' is the largest genus in the tribe Akodontini. Three of its synonyms—''Chalcomys'', ''Hypsimys'', and particularly ''Microxus''—have sometimes been regarded as distinct genera. Neomicroxus was separated in 2013. Previously associated with ''Akodon'', the genera ''Abrothrix'', '' Deltamys'', ''Necromys'', ''Thalpomys'', and '' Thaptomys'' are currently recognized as distinct. Some species of the tribe Abrotrichini are called akodons. The genus cont ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arctic Lemming
The Arctic lemming (''Dicrostonyx torquatus'') is a species of rodent in the family Cricetidae. Although generally classified as a "least concern" species, the Novaya Zemlya subspecies ''(Dicrostonyx torquatus ungulatus)'' is considered a vulnerable species under Russian nature conservation legislation (included in Red Book of Russian Federation since 1998). Biology It is found only in the Arctic biomes in the Russian Federation, and it is the most common mammal on Severnaya Zemlya. Specimens were once found in England, but they are now extirpated. For the most part, lemmings of the genus ''Lemmus'' can coexist with those of genus ''Dicrostonyx''. Arctic lemmings migrate when population density becomes too great, and they resort to swimming in search of a new habitat. The disappearance of lemmings and the lemming cycles in the Arctic have shown that they are the causes of fluctuations in local breeding among geese and waders. Recovery of lemmings after years of low density is as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wood Lemming
The wood lemming (''Myopus schisticolor'') is a species of rodent in the family Cricetidae. It belongs to the rodent subfamily Arvicolinae, so is a relative of the voles, lemmings, and muskrats. It is found in the taiga biome of China, Estonia, Finland, Mongolia, Norway, Russia, and Sweden. Sex determination Wood lemmings produce about three times as many female as male offspring. This is due to an unusual genetic system where they have two different types of X chromosomes, the normal X and a mutated X*. Females with that mutation on their X*-chromosome inhibit the male determining effect of the Y chromosome. This leads to three genetic types of females: XX, X*X and X*Y and one genetic type of males XY. The X*Y females are fertile, but only produce X* ova, which means they only produce female offspring. It is not fully known the extent to which nature balances out the differences in the adult population, but sampling studies seem to suggest males do make up as little as 25% of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Goat
The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the animal family Bovidae and the tribe Caprini, meaning it is closely related to the sheep. There are over 300 distinct breeds of goat.Hirst, K. Kris"The History of the Domestication of Goats".''About.com''. Accessed August 18, 2008. It is one of the oldest domesticated species of animal, according to archaeological evidence that its earliest domestication occurred in Iran at 10,000 calibrated calendar years ago. Goats have been used for milk, meat, fur, and skins across much of the world. Milk from goats is often turned into goat cheese. Female goats are referred to as ''does'' or ''nannies'', intact males are called ''bucks'' or ''billies'', and juvenile goats of both sexes are called ''kids''. Castrated males are called ''wethers''. Whil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature, ''Eohippus'', into the large, single-toed animal of today. Humans began domesticating horses around 4000 BCE, and their domestication is believed to have been widespread by 3000 BCE. Horses in the subspecies ''caballus'' are domesticated, although some domesticated populations live in the wild as feral horses. These feral populations are not true wild horses, as this term is used to describe horses that have never been domesticated. There is an extensive, specialized vocabulary used to describe equine-related concepts, covering everything from anatomy to life stages, size, colors, markings, breeds, locomotion, and behavior. Horses are adapted to run, allowing them to quickly escape predators, and po ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water Buffalo
The water buffalo (''Bubalus bubalis''), also called the domestic water buffalo or Asian water buffalo, is a large bovid originating in the Indian subcontinent and Southeast Asia. Today, it is also found in Europe, Australia, North America, South America and some African countries. Two extant types of water buffalo are recognized, based on morphological and behavioural criteria: the river buffalo of the Indian subcontinent and further west to the Balkans, Egypt and Italy and the swamp buffalo, found from Assam in the west through Southeast Asia to the Yangtze valley of China in the east. The wild water buffalo (''Bubalus arnee'') most likely represents the ancestor of the domestic water buffalo. Results of a phylogenetic study indicate that the river-type water buffalo probably originated in western India and was domesticated about 6,300 years ago, whereas the swamp-type originated independently from Mainland Southeast Asia and was domesticated about 3,000 to 7,000 years ago ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sex Steroid
Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effects are mediated by slow genomic mechanisms through nuclear receptors as well as by fast nongenomic mechanisms through membrane-associated receptors and signaling cascades. The polypeptide hormones luteinizing hormone, follicle-stimulating hormone and gonadotropin-releasing hormone – each associated with the gonadotropin axis – are usually not regarded as sex hormones, although they play major sex-related roles. Production Natural sex hormones are made by the gonads (ovaries or testes), by adrenal glands, or by conversion from other sex steroids in other tissue such as liver or fat. Image:Steroidogenesis.svg Image:Biosinthesis of steroid hormones (simplified version).jpg Image:Biosinthesis of steroid hormones (extended version).jpg Imag ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Temperature-dependent Sex Determination
Temperature-dependent sex determination (TSD) is a type of environmental sex determination in which the temperatures experienced during embryonic/larval development determine the sex of the offspring. It is only observed in reptiles and teleost fish. TSD differs from the chromosomal sex-determination systems common among vertebrates. It is the most studied type of environmental sex determination (ESD). Some other conditions, e.g. density, pH, and environmental background color, are also observed to alter sex ratio, which could be classified either as temperature-dependent sex determination or temperature-dependent sex differentiation, depending on the involved mechanisms. As sex-determining mechanisms, TSD and genetic sex determination (GSD) should be considered in an equivalent manner, which can lead to reconsidering the status of fish species that are claimed to have TSD when submitted to extreme temperatures instead of the temperature experienced during development in the wild, si ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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