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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] |
Environmental Sex Determination
Environmental sex determination is the establishment of sex by a non-genetic cue, such as nutrient availability, experienced within a discrete period after fertilization. Environmental factors which often influence sex determination during development or sexual maturation include light intensity and photoperiod, temperature, nutrient availability, and pheromones emitted by surrounding plants or animals. This is in contrast to genotypic sex determination, which establishes sex at fertilization by genetic factors such as sex chromosomes. Under true environmental sex determination, once sex is determined, it is fixed and cannot be switched again. Environmental sex determination is different from some forms of sequential hermaphroditism in which the sex is determined flexibly after fertilization throughout the organism’s life. Adaptive Significance Environmental sex determination is similar to certain forms of sexual selection in that there are oftentimes different and opposing s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intersex (biology)
Intersex is a general term for an organism that has sex characteristics that intermediate between male and female. The term intersex typically applies to abnormal members of gonochoric species that are usually sterile. It is not to be confused with the term hermaphrodite. Intersexuality has been reported in mammals, fishes, nematodes, and crustaceans. Mammals Intersex can also occur in non-human mammals such as pigs, with it being estimated that 0.1% to 1.4% of pigs are intersex. Depending on the definition, the prevalence of intersex among humans have been reported to be about 0.018%. Nematodes Intersex is known to occur in all main groups of nematodes. Most of them are functionally female. Male intersexes with female characteristics have been reported but are less common. Fishes Gonadal intersex also occurs in fishes, where the individual has both ovarian and testicular tissue. Although it is a rare anomaly among gonochoric fishes, it is a transitional state in fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steroidogenesis
A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and as signaling molecules. Hundreds of steroids are found in plants, animals and fungi. All steroids are manufactured in cells from the sterols lanosterol ( opisthokonts) or cycloartenol (plants). Lanosterol and cycloartenol are derived from the cyclization of the triterpene squalene. The steroid core structure is typically composed of seventeen carbon atoms, bonded in four " fused" rings: three six-member cyclohexane rings (rings A, B and C in the first illustration) and one five-member cyclopentane ring (the D ring). Steroids vary by the functional groups attached to this four-ring core and by the oxidation state of the rings. Sterols are forms of steroids with a hydroxy group at position three and a skeleton derived from cholestane. ''Al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aromatase
Aromatase (), also called estrogen synthetase or estrogen synthase, is an enzyme responsible for a key step in the biosynthesis of estrogens. It is CYP19A1, a member of the cytochrome P450 superfamily, which are monooxygenases that catalyze many reactions involved in steroidogenesis. In particular, aromatase is responsible for the aromatization of androgens into estrogens. The enzyme aromatase can be found in many tissues including gonads ( granulosa cells), brain, adipose tissue, placenta, blood vessels, skin, and bone, as well as in tissue of endometriosis, uterine fibroids, breast cancer, and endometrial cancer. It is an important factor in sexual development. Function Aromatase is localized in the endoplasmic reticulum where it is regulated by tissue-specific promoters that are in turn controlled by hormones, cytokines, and other factors. It catalyzes the last steps of estrogen biosynthesis from androgens (specifically, it transforms androstenedione to estrone and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aromatase Inhibitor
Aromatase inhibitors (AIs) are a class of drugs used in the treatment of breast cancer in postmenopausal women and in men, and gynecomastia in men. They may also be used off-label to reduce estrogen conversion when supplementing testosterone exogenously. They may also be used for chemoprevention in women at high risk for breast cancer. Aromatase is the enzyme that catalyzes a key aromatization step in the synthesis of estrogen. It converts the enone ring of androgen precursors such as testosterone, to a phenol, completing the synthesis of estrogen. As such, AIs are estrogen synthesis inhibitors. Because hormone-positive breast and ovarian cancers are dependent on estrogen for growth, AIs are taken to either block the production of estrogen or block the action of estrogen on receptors. Medical uses Cancer In contrast to premenopausal women, in whom most of the estrogen is produced in the ovaries, in postmenopausal women estrogen is mainly produced in peripheral tissues of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Testosterone
Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteristics such as increased muscle and bone mass, and the growth of body hair. In addition, testosterone in both sexes is involved in health and well-being, including moods, behaviour, and in the prevention of osteoporosis. Insufficient levels of testosterone in men may lead to abnormalities including frailty and bone loss. Testosterone is a steroid from the androstane class containing a ketone and a hydroxyl group at positions three and seventeen respectively. It is biosynthesized in several steps from cholesterol and is converted in the liver to inactive metabolites. It exerts its action through binding to and activation of the androgen receptor. In humans and most other vertebrates, testosterone is secreted primarily by the testicles of m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Estradiol
Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development of female secondary sexual characteristics such as the breasts, widening of the hips and a female-associated pattern of fat distribution. It is also important in the development and maintenance of female reproductive tissues such as the mammary glands, uterus and vagina during puberty, adulthood and pregnancy. It also has important effects in many other tissues including bone, fat, skin, liver, and the brain. Though estradiol levels in males are much lower than in females, estradiol has important roles in males as well. Apart from humans and other mammals, estradiol is also found in most vertebrates and crustaceans, insects, fish, and other animal species. Estradiol is produced especially within the follicles of the ovaries, but al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synergy
Synergy is an interaction or cooperation giving rise to a whole that is greater than the simple sum of its parts. The term ''synergy'' comes from the Attic Greek word συνεργία ' from ', , meaning "working together". History In Christian theology, synergism is the idea that salvation involves some form of cooperation between divine grace and human freedom. The words ''synergy'' and ''synergetic'' have been used in the field of physiology since at least the middle of the 19th century: SYN'ERGY, ''Synergi'a'', ''Synenergi'a'', (F.) ''Synergie''; from ''συν'', 'with', and ''εργον'', 'work'. A correlation or concourse of action between different organs in health; and, according to some, in disease. :—Dunglison, Roble''Medical Lexicon''Blanchard and Lea, 1853 In 1896, Henri Mazel applied the term "synergy" to social psychology by writing ''La synergie sociale'', in which he argued that Darwinian theory failed to account of "social synergy" or "social love", a col ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Red-eared Slider
The red-eared slider or red-eared terrapin (''Trachemys scripta elegans'') is a subspecies of the pond slider (''Trachemys scripta''), a semiaquatic turtle belonging to the family Emydidae. It is the most popular pet turtle in the United States, is also popular as a pet across the rest of the world, and is the most invasive turtle. It is the most commonly traded turtle in the world. The red-eared slider is native from the Midwestern United States to northern Mexico, but has become established in other places because of pet releases, and has become invasive in many areas where it outcompetes native species. The red-eared slider is included in the list of the world's 100 most invasive species. Etymology The red-eared slider gets its name from the small, red stripe around its ears, or where its ears would be, and from its ability to slide quickly off rocks and logs into the water. This species was previously known as Troost's turtle in honor of an American herpetologist G ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NBC News
NBC News is the news division of the American broadcast television network NBC. The division operates under NBCUniversal Television and Streaming, a division of NBCUniversal, which is, in turn, a subsidiary of Comcast. The news division's various operations report to the president of NBC News, Noah Oppenheim. The NBCUniversal News Group also comprises MSNBC, the network's 24-hour general news channel, business and consumer news channels CNBC and CNBC World, the Spanish language Noticias Telemundo and United Kingdom–based Sky News. NBC News aired the first regularly scheduled news program in American broadcast television history on February 21, 1940. The group's broadcasts are produced and aired from 30 Rockefeller Plaza, NBCUniversal's headquarters in New York City. The division presides over America's number-one-rated newscast, '' NBC Nightly News'', the world's first of its genre morning television program, '' Today'', and the longest-running television series in Ame ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eastern Bearded Dragon
The eastern bearded dragon (''Pogona barbata''), also known as common bearded dragon or simply bearded lizard, is an agamid lizard found in wooded parts of Australia. It is one of a group of species known commonly as bearded dragons. Other common names for this species include Jew lizard and frilly lizard, the latter being a confusion between this and another dragon, the frill-necked lizard (''Chlamydosaurus kingii''). This species was originally described in 1829 by Georges Cuvier, who named it ''Amphibolurus barbatus''. Description ''P. barbata'' is one of the eight recognized species within the genus ''Pogona''. Adult males can grow to about from the snout to the tip of the tail, while females may reach in overall length. The head is large and triangular in shape. The throat is covered with spiny, dark grey scales which can be raised to form an impressive "beard". Several groups of even longer spiny scales are located at the back of the head, the corners of the mouth, the e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Madeleine Charnier
Madeleine Simonne Charnier (15 June 1919—9 July 2002) was a French zoologist. She is known for having first described temperature-dependent sex determination in 1966. Biography Charnier's mother was a mathematics professor. Charnier received her license in science around 1935 at the Faculty of Sciences in Paris. She moved to Africa around 1945 to join her brother: first to Kaolack, Senegal, then to Cotonou, Dahomey (now Benin), then to Dakar, Senegal at the end of the 1940s. In 1953, she divorced her husband, Marcel Robert. That year, she was hired at the university library of University of Dakar. From 1955, Charnier worked at the faculty of medicine in parasitology, and received certificates in coprology and hematology. There, she published her first scientific article on the common agama, which would become her preferred species to research for the next ten years (Charnier and Dutarte 1956). In 1958, she left the faculty of medicine for the Faculty of Sciences at the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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