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Topic Review
White Tiger
The white tiger or bleached tiger is a pigmentation variant of the Bengal tiger, which is reported in the wild from time to time in the Indian states of Madhya Pradesh, Assam, West Bengal and Bihar in the Sunderbans region and especially in the former State of Rewa. Such a tiger has the black stripes typical of the Bengal tiger, but carries a white or near-white coat.
  • 9.1K
  • 19 Oct 2022
Topic Review
Vision in Fishes
Vision is an important sensory system for most species of fish. Fish eyes are similar to the eyes of terrestrial vertebrates like birds and mammals, but have a more spherical lens. Birds and mammals (including humans) normally adjust focus by changing the shape of their lens, but fish normally adjust focus by moving the lens closer to or further from the retina. Fish retinas generally have both rod cells and cone cells (for scotopic and photopic vision), and most species have colour vision. Some fish can see ultraviolet and some are sensitive to polarized light. Among jawless fishes, the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. The ancestors of modern hagfish, thought to be the protovertebrate were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. Fish vision shows evolutionary adaptation to their visual environment, for example deep sea fish have eyes suited to the dark environment.
  • 8.7K
  • 10 Nov 2022
Topic Review
Essential Trace Elements
Trace elements produce double-edged effects on the lives of animals and particularly of humans. On one hand, these elements represent potentially toxic agents; on the other hand, they are essentially needed to support growth and development and confer protection against disease. The amount taken up and the accumulation in human tissues decisively control whether the exerted effects are toxic or beneficial. This entry provides a brief description of some toxic, likely essential and essential elements and their influence on human health.
  • 8.0K
  • 20 Aug 2020
Topic Review
Responses to Sneezing
In English-speaking countries, the common verbal response to another person's sneeze is "bless you", or, less commonly in the United States and Canada , "Gesundheit", the German word for health (and the response to sneezing in German-speaking countries). There are several proposed bless-you origins for use in the context of sneezing. In non-English-speaking cultures, words referencing good health or a long life are often used instead of "bless you," though some also use references to God. In some Asian cultures such as Korean and Japanese cultures, the practice of responding to another person's sneeze does not exist. In the Assyrian language, “Shemad Alaha”, “in God’s name”, is the response to a sneeze.
  • 7.6K
  • 01 Dec 2022
Topic Review
Intergeneric Hybrid
In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in blending inheritance), but can show hybrid vigor, sometimes growing larger or taller than either parent. The concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in the individual parentage. In genetics, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how closely related the parent species are. Species are reproductively isolated by strong barriers to hybridisation, which include genetic and morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo. Some act before fertilization and others after it. Similar barriers exist in plants, with differences in flowering times, pollen vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and the structure of the chromosomes. A few animal species and many plant species, however, are the result of hybrid speciation, including important crop plants such as wheat, where the number of chromosomes has been doubled. Human impact on the environment has resulted in an increase in the interbreeding between regional species, and the proliferation of introduced species worldwide has also resulted in an increase in hybridisation. This genetic mixing may threaten many species with extinction, while genetic erosion from monoculture in crop plants may be damaging the gene pools of many species for future breeding. A form of often intentional human-mediated hybridisation is the crossing of wild and domesticated species. This is common in both traditional horticulture and modern agriculture; many commercially useful fruits, flowers, garden herbs, and trees have been produced by hybridisation. One such flower, Oenothera lamarckiana, was central to early genetics research into mutationism and polyploidy. It is also more occasionally done in the livestock and pet trades; some well-known wild × domestic hybrids are beefalo and wolfdogs. Human selective breeding of domesticated animals and plants has resulted in the development of distinct breeds (usually called cultivars in reference to plants); crossbreeds between them (without any wild stock) are sometimes also imprecisely referred to as "hybrids". Hybrid humans existed in prehistory. For example, Neanderthals and anatomically modern humans are thought to have interbred as recently as 40,000 years ago. Mythological hybrids appear in human culture in forms as diverse as the Minotaur, blends of animals, humans and mythical beasts such as centaurs and sphinxes, and the Nephilim of the Biblical apocrypha described as the wicked sons of fallen angels and attractive women.
  • 7.3K
  • 10 Oct 2022
Topic Review
Tetrapod
Tetrapods (/ˈtɛtrəˌpɒdz/; from grc τετρα- (tetra-) 'four', and πούς (poús) 'foot') are four-limbed vertebrate animals constituting the superclass Tetrapoda (/tɛˈtrɒpədə/). It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids (including mammals). Tetrapods evolved from a group of animals known as the Tetrapodomorpha which, in turn, evolved from ancient lobe-finned (sarcopterygian) fish around 390 million years ago in the middle Devonian period; their forms were transitional between lobe-finned fishes and the four-limbed tetrapods. Limbed vertebrates (tetrapods in the broad sense of the word) are first known from Middle Devonian trackways, and body fossils became common near the end of the Late Devonian but these were all aquatic. The first crown-tetrapods (last common ancestors of extant tetrapods capable of terrestrial locomotion) appeared by the very early Carboniferous, 350 million years ago. The specific aquatic ancestors of the tetrapods and the process by which they colonized Earth's land after emerging from water remains unclear. The change from a body plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known. Tetrapods have numerous anatomical and physiological features that are distinct from their aquatic ancestors. These include the structure of the head for feeding and breathing, limb girdles and digits for locomotion, eyes for seeing, ears for hearing, and the heart and lungs for gas circulation and exchange outside water. The first tetrapods (stem) or "fishapods" were primarily aquatic. Modern amphibians, which evolved from earlier groups, are generally semiaquatic; the first stage of their lives is as fish-like tadpoles, and later stages are partly terrestrial and partly aquatic. However, most tetrapod species today are amniotes, most of which are terrestrial tetrapods whose branch evolved from earlier tetrapods early in the Late Carboniferous. The key innovation in amniotes over amphibians is the amnion, which enables the eggs to retain their aqueous contents on land, rather than needing to stay in water. (Some amniotes later evolved internal fertilization, although many aquatic species outside the tetrapod tree had evolved such before the tetrapods appeared, e.g. Materpiscis.) Some tetrapods, such as snakes and caecilians, have lost some or all of their limbs through further speciation and evolution; some have only concealed vestigial bones as a remnant of the limbs of their distant ancestors. Others returned to being amphibious or otherwise living partially or fully aquatic lives, the first during the Carboniferous period, others as recently as the Cenozoic. One group of amniotes diverged into the reptiles, which includes lepidosaurs, dinosaurs (which includes birds), crocodilians, turtles, and extinct relatives; while another group of amniotes diverged into the mammals and their extinct relatives. Amniotes include the tetrapods that further evolved for flight—such as birds from among the dinosaurs, pterosaurs from the archosaurs, and bats from among the mammals.
  • 7.0K
  • 04 Nov 2022
Topic Review
Frog
A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally without tail in Ancient Greek). The oldest fossil "proto-frog" Triadobatrachus is known from the Early Triassic of Madagascar , but molecular clock dating suggests their split from other amphibians may extend further back to the Permian, 265 million years ago. Frogs are widely distributed, ranging from the tropics to subarctic regions, but the greatest concentration of species diversity is in tropical rainforest. Frogs account for around 88% of extant amphibian species. They are also one of the five most diverse vertebrate orders. Warty frog species tend to be called toads, but the distinction between frogs and toads is informal, not from taxonomy or evolutionary history. An adult frog has a stout body, protruding eyes, anteriorly-attached tongue, limbs folded underneath, and no tail (the tail of tailed frogs is an extension of the male cloaca). Frogs have glandular skin, with secretions ranging from distasteful to toxic. Their skin varies in colour from well-camouflaged dappled brown, grey and green to vivid patterns of bright red or yellow and black to show toxicity and ward off predators. Adult frogs live in fresh water and on dry land; some species are adapted for living underground or in trees. Frogs typically lay their eggs in water. The eggs hatch into aquatic larvae called tadpoles that have tails and internal gills. They have highly specialized rasping mouth parts suitable for herbivorous, omnivorous or planktivorous diets. The life cycle is completed when they metamorphose into adults. A few species deposit eggs on land or bypass the tadpole stage. Adult frogs generally have a carnivorous diet consisting of small invertebrates, but omnivorous species exist and a few feed on plant matter. Frog skin has a rich microbiome which is important to their health. Frogs are extremely efficient at converting what they eat into body mass. They are an important food source for predators and part of the food web dynamics of many of the world's ecosystems. The skin is semi-permeable, making them susceptible to dehydration, so they either live in moist places or have special adaptations to deal with dry habitats. Frogs produce a wide range of vocalizations, particularly in their breeding season, and exhibit many different kinds of complex behaviors to attract mates, to fend off predators and to generally survive. Frogs are valued as food by humans and also have many cultural roles in literature, symbolism and religion. They are also seen as environmental bellwethers, with declines in frog populations often viewed as early warning signs of environmental damage. Frog populations have declined significantly since the 1950s. More than one third of species are considered to be threatened with extinction and over 120 are believed to have become extinct since the 1980s. The number of malformations among frogs is on the rise and an emerging fungal disease, chytridiomycosis, has spread around the world. Conservation biologists are working to understand the causes of these problems and to resolve them.
  • 5.8K
  • 19 Oct 2022
Biography
Mirza Ghulam Ahmad
Mirzā Ghulām Ahmad (13 February 1835 – 26 May 1908) was an Indian religious leader and the founder of the Ahmadiyya movement in Islam. He claimed to have been divinely appointed as the promised Messiah and Mahdi—which is the metaphorical second-coming of Jesus (mathīl-iʿIsā),[1][2] in fulfillment of Islam's latter day prophecies, as well as the Mujaddid (centennial reviver) of the 14th
  • 5.7K
  • 15 Nov 2022
Biography
Nikolai Aleksandrovich Kozyrev
Nikolai Alexandrovich Kozyrev (Russian: Никола́й Алекса́ндрович Ко́зырев; 2 September 1908 – 27 February 1983) was a Soviet astronomer/astrophysicist. He was born in St. Petersburg, and by 1928 he had graduated from the Leningrad State University. In 1931 he began working at the Pulkovo Observatory, located to the south of Leningrad. He was considered to be one
  • 5.5K
  • 30 Dec 2022
Topic Review
Causes of Transsexuality
The study of the causes of transsexuality investigates gender identity formation of transgender people, especially those who are transsexual. Transgender people have a gender identity that does not match their assigned sex, often resulting in gender dysphoria. The causes of transsexuality have been studied for decades. The most studied factors are biological, especially brain structure differences in relation to biology and sexual orientation. Environmental factors have also been proposed. Transgender brain studies, especially those on trans women who are sexually attracted to women (gynephilic), and those on trans men who are sexually attracted to men (androphilic), are limited, as they include a small number of tested individuals. The available research indicates that the brain structure of androphilic trans women with early-onset gender dysphoria is closer to the brain structure of cisgender women's and less like cisgender men's. It also reports that both androphilic trans women and trans women with late-onset gender dysphoria who are gynephilic have different brain phenotypes, and that gynephilic trans women differ from both cisgender female and male controls in non-dimorphic brain areas. Cortical thickness, which is generally thicker in cisgender women's brains than in cisgender men's brains, may also be thicker in trans women's brains, but is present in a different location to cisgender women's brains. For trans men, research indicates that those with early-onset gender dysphoria and who are gynephilic have brains that generally correspond to their assigned sex, but that they have their own phenotype with respect to cortical thickness, subcortical structures, and white matter microstructure, especially in the right hemisphere. Hormone use can also affect transgender people's brain structure; it can cause transgender women's brains to become closer to those of cisgender women, and morphological increments observed in the brains of trans men might be due to the anabolic effects of testosterone. Twin studies suggest that there are likely genetic causes of transsexuality, although the precise genes involved are not fully understood. One study published in the International Journal of Transgender Health found that 20% of identical twin pairs in which at least one twin was trans were both trans, compared to only 2.6% of non-identical twins who were raised in the same family at the same time, but were not genetically identical. Ray Blanchard created a taxonomy of male-to-female transsexualism that proposes two distinct etiologies for androphilic and gynephilic individuals that has become controversial, supported by J. Michael Bailey, Anne Lawrence, James Cantor and others, but opposed by Charles Allen Moser, Julia Serano, and the World Professional Association for Transgender Health.
  • 5.5K
  • 20 Oct 2022
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