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X0 Sex-determination System
The XO sex-determination system (sometimes X0 sex-determination system) is a system that some species of insects, arachnids, and mammals use to determine the sex of offspring. In this system, there is only one sex chromosome, referred to as X. Males only have one X chromosome (XO), while females have two (XX). The letter O (sometimes a zero) signifies the lack of a second X. Maternal gametes always contain an X chromosome, so the sex of the animals' offspring depends on whether a sex chromosome is present in the male gamete. Its sperm normally contains either one X chromosome or no sex chromosomes at all. This system determines the sex of offspring among: * Most arachnidsBull, James J.; ''Evolution of sex determining mechanisms''; p. 17 with the exception of mites where a small majority are haplodiploid, * Almost all apterygote and Paleopteran insects (e.g., dragonflies, silverfish) * Most exopterygote insects (e.g., grasshoppers, crickets, cockroaches) * Some nematodes, crus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Critique Of The Theory Of Evolution Fig 060
Critique is a wikt:method, method of disciplined, systematic study of a written or oral discourse. Although critique is commonly understood as fault finding and negative judgment,Rodolphe Gasché (2007''The honor of thinking: critique, theory, philosophy''pp. 12–13 quote: it can also involve merit recognition, and in the philosophical tradition it also means a methodical practice of doubt. The contemporary sense of critique has been largely influenced by the Age of Enlightenment, Enlightenment critique of prejudice and authority, which championed the emancipation and autonomy from religious and political authorities. The term ''critique'' derives, via French, from (), meaning "the faculty of judging", that is, discerning the value of persons or things. Critique is also known as major logic, as opposed to minor logic or dialectics. Critique in philosophy Philosophy is the application of critical thought, and is the disciplined practice of processing the ''theory/praxis pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ancistrus
''Ancistrus'' is a genus of nocturnal freshwater fish in the family Loricariidae of order Siluriformes, native to freshwater habitats in South America and Panama. Fish of this genus are common in the aquarium trade where they are known as bushynose or bristlenose catfish. In the aquarium hobby they are often referred to as bushynose or bristlenose plecos instead, but this may lead to confusion as "pleco" usually is used for ''Hypostomus plecostomus'' and its allies and is often used as a catchall term for any loricariids remotely resembling that species. Taxonomy The type species is ''Ancistrus cirrhosus''. This genus is the largest genus within the tribe Ancistrini. The name ancistrus derives from the Ancient Greek ''agkistron'' "hook" – a reference to the form of the cheek odontodes. The genera ''Pristiancistrus'', ''Thysanocara'' and ''Xenocara'' are now synonyms of ''Ancistrus''. Description ''Ancistrus'' species show all the typical features of the Loricariidae. T ... [...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 Gametophyte, 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Y Chromosome
The Y chromosome is one of two sex chromosomes (allosomes) in therian mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or absence of Y that determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the gene SRY, which triggers male development. The DNA in the human Y chromosome is composed of about 59 million base pairs, making it similar in size to chromosome 19. The Y chromosome is passed only from father to son. With a 30% difference between humans and chimpanzees, the Y chromosome is one of the fastest-evolving parts of the human genome. The human Y chromosome carries an estimated 100–200 genes, with between 45 and 73 of these being protein-coding. All single-copy Y-linked genes are hemizygous (present on only one chromosome) except in cases of aneuploidy such as XYY syndrome or XXYY syndrome. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drosophila
''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit. They should not be confused with the Tephritidae, a related family, which are also called fruit flies (sometimes referred to as "true fruit flies"); tephritids feed primarily on unripe or ripe fruit, with many species being regarded as destructive agricultural pests, especially the Mediterranean fruit fly. One species of ''Drosophila'' in particular, ''D. melanogaster'', has been heavily used in research in genetics and is a common model organism in developmental biology. The terms "fruit fly" and "''Drosophila''" are often used synonymously with ''D. melanogaster'' in modern biological literature. The entire genus, however, contains more than 1,500 species and is very diverse in appearance, be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Caenorhabditis Elegans
''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek ''caeno-'' (recent), ''rhabditis'' (rod-like) and Latin ''elegans'' (elegant). In 1900, Maupas initially named it '' Rhabditides elegans.'' Osche placed it in the subgenus ''Caenorhabditis'' in 1952, and in 1955, Dougherty raised ''Caenorhabditis'' to the status of genus. ''C. elegans'' is an unsegmented pseudocoelomate and lacks respiratory or circulatory systems. Most of these nematodes are hermaphrodites and a few are males. Males have specialised tails for mating that include spicules. In 1963, Sydney Brenner proposed research into ''C. elegans,'' primarily in the area of neuronal development. In 1974, he began research into the molecular and developmental biology of ''C. elegans'', which has since been extensively used as a model organism. It was the first multicellu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Model Organism
A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Model organisms are widely used to research human disease when human experimentation would be unfeasible or unethical. This strategy is made possible by the common descent of all living organisms, and the conservation of metabolic and developmental pathways and genetic material over the course of evolution. Studying model organisms can be informative, but care must be taken when generalizing from one organism to another. In researching human disease, model organisms allow for better understanding the disease process without the added risk of harming an actual human. The species chosen will usually meet a determined taxonomic equivalency to humans, so as to react to disease or its treatment in a way that resembles ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hermaphrodite
In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrates) do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the female or male. For example, the great majority of tunicata, tunicates, pulmonate molluscs, opisthobranch, earthworms, and slugs are hermaphrodites. Hermaphroditism is also found in some fish species and to a lesser degree in other vertebrates. Most plants are also hermaphrodites. Animal species having different sexes, male and female, are called Gonochorism, gonochoric, which is the opposite of hermaphrodite. There are also species where hermaphrodites exist alongside males (called androdioecy) or alongside females (called gynodioecy), or all three exist in the same species ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tokunoshima Spiny Rat
The Tokunoshima spiny rat (''Tokudaia tokunoshimensis'') is a rodent found only on the island of Tokunoshima in the Ryukyu Islands of Japan. Due to its small habitat, it is considered endangered. It is commonly found in the secondary and primary subtropical moist broadleaf forests of this island. The karyotype has an odd diploid number, 2n = 45. Like its relative '' T. osimensis'', it is one of the few mammals that lack a Y chromosome and ''SRY'' gene. The species is threatened by deforestation and predation by feral cats and dogs. See also * ''Ellobius lutescens'' * ''Ellobius tancrei The Zaisan mole vole (''Ellobius tancrei''), or eastern mole vole, is a species of rodent in the family Cricetidae. It is found in central Asia. Description The Zaisan mole vole is highly adapted to life underground. It grows to a head and body ...'' References Tokudaia Endemic mammals of Japan Endemic fauna of the Ryukyu Islands Mammals described in 2006 {{Murinae-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ryukyu Spiny Rat
The Ryukyu spiny rat (''Tokudaia osimensis'') is a species of rodent in the family Muridae. Endemic to Amami Ōshima island in the Amami Islands of the Ryukyu archipelago of Japan, its natural habitat is subtropical moist broadleaf forest. The karyotype has an odd diploid number, 2n = 25. Like its relative '' T. tokunoshimensis'', it has lost its Y chromosome and ''SRY'' gene. The species is threatened by habitat destruction and fragmentation, predation by feral cats and dogs and introduced mongooses, and competition with introduced black rat The black rat (''Rattus rattus''), also known as the roof rat, ship rat, or house rat, is a common long-tailed rodent of the stereotypical rat genus ''Rattus'', in the subfamily Murinae. It likely originated in the Indian subcontinent, but is n ...s. See also * '' Ellobius lutescens'' * '' Ellobius tancrei'' References Y-chromosome - Will it or will it not, hold on? Rats of Asia Endemic mammals of Japan Endemic f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gambian Epauletted Fruit Bat
The Gambian epauletted fruit bat (''Epomophorus gambianus'') is a species of megabat in the family Pteropodidae. It is found in Benin, Burkina Faso, Cameroon, Central African Republic, Chad, Democratic Republic of the Congo, Ivory Coast, Ethiopia, Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Niger, Nigeria, Senegal, Sierra Leone, South Sudan, Sudan, and Togo. Its natural habitats are subtropical or tropical dry forests and savanna. Populations of epauletted fruit bats are threatened by pesticides on fruit, human disturbance and over-collecting in the past. However, the number one reason it may be threatened is habitat destruction. Mostly found in Africa, these creatures have grayish-brown color fur with a white patch at the base of their ear in both males and females. These fruit bats are also very noisy creatures. In the context of mating behavior (see "Reproduction" below), adult males may hang from perches and perform a calling-display during which they utter a modera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peters's Epauletted Fruit Bat
The Peters's epauletted fruit bat (''Epomophorus crypturus'') is a species of megabat in the family Pteropodidae. It is found in Angola, Botswana, Democratic Republic of the Congo, Eswatini, Malawi, Mozambique, Namibia, Tanzania, Zambia, and Zimbabwe. Its natural habitat is in riverine or evergreen forest, or moist woodland, where there are fruit-bearing trees. Taxonomy It was described as a new species in 1852 by German naturalist Wilhelm Peters. Peters collected the holotype in "Tette" in Mozambique during an expedition that occurred from 1842 to 1848. Description Individuals have a forearm length ranging from and weigh . It consumes plant matter such as fruit and nectar. For reproduction, the typical litter size is one, though twins are perhaps possible, if very rare. Newborns are altricial at birth, with eyes closed and sparse fur. Newborns weigh around . Births likely occur around September, and it has been suggested that females give birth once per year. It has variable r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
