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Simple Mendelian Genetics In Humans
Mendelian traits behave according to the model of monogenic or simple gene inheritance in which one gene corresponds to one trait. Discrete traits (as opposed to continuously varying traits such as height) with simple Mendelian inheritance patterns are relatively rare in nature, and many of the clearest examples in humans cause disorders. Discrete traits found in humans are common examples for teaching genetics. Mendelian model According to the model of Mendelian inheritance, alleles may be dominant or recessive, one allele is inherited from each parent, and only those who inherit a recessive allele from each parent exhibit the recessive phenotype. Offspring with either one or two copies of the dominant allele will display the dominant phenotype. Very few phenotypes are purely Mendelian traits. Common violations of the Mendelian model include incomplete dominance, codominance, genetic linkage, environmental effects, and quantitative contributions from a number of genes (see: ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mendelian Inheritance
Mendelian inheritance (also known as Mendelism) is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later popularized by William Bateson. These principles were initially controversial. When Mendel's theories were integrated with the Boveri–Sutton chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics. Ronald Fisher combined these ideas with the theory of natural selection in his 1930 book '' The Genetical Theory of Natural Selection'', putting evolution onto a mathematical footing and forming the basis for population genetics within the modern evolutionary synthesis. History The principles of Mendelian inheritance were named for and first derived by Gregor Johann Mendel, a nineteenth-century Moravian monk who formulated his ideas after conducting simple hybridization experiments with pea p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sinus Bradycardia
Sinus bradycardia is a sinus rhythm with a reduced rate of electrical discharge from the sinoatrial node, resulting in a bradycardia, a heart rate that is lower than the normal range (60–100 beats per minute for adult humans). Signs and symptoms The decreased heart rate can cause a decreased cardiac output resulting in symptoms such as lightheadedness, dizziness, hypotension, vertigo, and syncope. The slow heart rate may also lead to atrial, junctional, or ventricular ectopic rhythms. Bradycardia is not necessarily problematic. People who practice sports may have sinus bradycardia, because their trained hearts can pump enough blood in each contraction to allow a low resting heart rate. Sinus bradycardia can also be an adaptive advantage; for example, diving seals may have a heart rate as low as 12 beats per minute, helping them to conserve oxygen during long dives. Sinus bradycardia is a common condition found in both healthy individuals and those who are considered well- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Huntington's Disease
Huntington's disease (HD), also known as Huntington's chorea, is an incurable neurodegenerative disease that is mostly Genetic disorder#Autosomal dominant, inherited. It typically presents as a triad of progressive psychiatric, cognitive, and motor symptoms. The earliest symptoms are often subtle problems with mood or mental/psychiatric abilities, which precede the motor symptoms for many people. The definitive physical symptoms, including a general Ataxia, lack of coordination and an unsteady human gait, gait, eventually follow. Over time, the basal ganglia region of the brain gradually Basal ganglia disease#Huntington's disease, becomes damaged. The disease is primarily characterized by a distinctive hyperkinesia, hyperkinetic movement disorder known as ''chorea.'' Chorea classically presents as uncoordinated, involuntary, "dance-like" body movements that become more apparent as the disease advances. Physical abilities gradually worsen until Motor coordination, coordinated mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Marfan Syndrome
Marfan syndrome (MFS) is a multi-systemic genetic disorder that affects the connective tissue. Those with the condition tend to be tall and thin, with dolichostenomelia, long arms, legs, Arachnodactyly, fingers, and toes. They also typically have hypermobility (joints), exceptionally flexible joints and scoliosis, abnormally curved spines. The most serious complications involve the heart and aorta, with an increased risk of mitral valve prolapse and aortic aneurysm. The lungs, eyes, bones, and the dura mater, covering of the spinal cord are also commonly affected. The severity of the symptoms is variable. MFS is caused by a mutation in ''FBN1'', one of the genes that make fibrillin, which results in abnormal connective tissue. It is an autosomal dominant disorder. In about 75% of cases, it is inherited from a parent with the condition, while in about 25% it is a new mutation. Diagnosis is often based on the Ghent criteria, family history and genetic testing (DNA analysis). Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Roman Nose
An aquiline nose is a human nose with a prominent bridge, giving it the appearance of being curved or slightly bent. The word ''aquiline'' comes from the Latin word ' ("eagle-like"), an allusion to the curved beak of an eagle. While some have ascribed the aquiline nose to specific ethnic, racial, or geographic groups, and in some cases associated it with other supposed non-physical characteristics (i.e. intelligence, status, personality, etc.—''see below''), no scientific studies or evidence support any such linkage. As with many phenotypical expressions (e.g. ' widow's peak', eye color, earwax type) it is found in many geographically diverse populations. In racist discourse In racist discourse, especially that of post- Enlightenment Western writers, a Roman nose has been characterized as a marker of beauty and nobility. A well-known example of the aquiline nose as a marker contrasting the bearer with their contemporaries is the protagonist of Aphra Behn's '' Oroonoko'' (168 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earwax
Earwax, also known by the medical term cerumen, is a waxy substance secreted in the ear canal of humans and other mammals. Earwax can be many colors, including brown, orange, red, yellowish, and gray. Earwax protects the skin of the human ear canal, assists in cleaning and lubrication, and provides protection against bacteria, fungi, particulate matter, and water. Major components of earwax include cerumen, produced by a type of modified sweat gland, and sebum, an oily substance. Both components are made by glands located in the outer ear canal. The chemical composition of earwax includes saturated and unsaturated long chain fatty acids, alcohols, squalene, and cholesterol. Earwax also contains dead skin cells and hair. Excess or compacted cerumen is the buildup of ear wax causing a blockage in the ear canal and it can press against the eardrum or block the outside ear canal or hearing aids, potentially causing hearing loss. Physiology Cerumen is produced in the ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Freckles
Freckles are clusters of concentrated melaninized cells which are most easily visible on people with a fair complexion. Freckles do not have an increased number of the melanin-producing cells, or melanocytes, but instead have melanocytes that overproduce melanin granules ( melanosomes) changing the coloration of the outer skin cells (keratinocytes). As such, freckles are different from lentigines and moles, which are caused by accumulation of melanocytes in a small area. Freckles can appear on all types of skin tones. Of the six Fitzpatrick skin types, they are most common on skin tones 1 and 2, which usually belong to North Europeans. However, it can also be found on people all over the world. In England a historical term for freckles is summer-voys, sometimes spelt summervoise, which may be related to the German term ''Sommersprossen''. Biology The formation of freckles is caused by exposure to sunlight. The exposure to UV-B radiation activates melanocytes to increase mela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cleft Chin
The chin is the forward pointed part of the anterior mandible ( mental region) below the lower lip. A fully developed human skull has a chin of between 0.7 cm and 1.1 cm. Evolution The presence of a well-developed chin is considered to be one of the morphological characteristics of ''Homo sapiens'' that differentiates them from other human ancestors such as the closely related Neanderthals. Early human ancestors have varied symphysial morphology, but none of them have a well-developed chin. The origin of the chin is traditionally associated with the anterior–posterior breadth shortening of the dental arch or tooth row; however, its general mechanical or functional advantage during feeding, developmental origin, and link with human speech, physiology, and social influence are highly debated. Functional perspectives Robinson (1913) suggests that the demand to resist masticatory stresses triggered bone thickening in the mental region of the mandible and ultimately formed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hair Whorl
A hair whorl (also known as a crown, swirl, or trichoglyph) is a patch of hair growing in a circular direction around a visible center point. Hair whorls occur in most hairy animals on the body as well as on the head, and can be either clockwise, counterclockwise or diffuse in direction of growth. In human theories Hair whorls on the head ( parietal whorls) have been studied by some behaviorists. Most people have clockwise scalp hair-whorls. Parietal whorls which are considered to be normal scalp patterns could be a single whorl or double whorls. Cases of triple parietal whorls are less common. Amar J. S. Klar conducted research to see if there was a genetic link between handedness and hair-whorl direction. He found that 8.4% of right-handed people and 45% of left-handed people have counterclockwise hair-whorls. His research suggested that a single gene may control both handedness and hair-whorl direction.Human handedness and scalp hair-whorl direction develop from a common ge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earlobe
The human earlobe (''lobulus auriculae''), the lower portion of the outer ear, is composed of tough areolar and adipose connective tissues, lacking the firmness and elasticity of the rest of the auricle (the external structure of the ear). In some cases the lower lobe is connected to the side of the face. Since the earlobe does not contain cartilage it has a large blood supply and may help to warm the ears. However, earlobes are not generally considered to have any major biological function. The earlobe contains many nerve endings, and for some people is an erogenous zone. The zoologist Desmond Morris in his book ''The Naked Ape'' (1967) conjectured that the lobes developed as an additional erogenous zone to facilitate the extended sexuality necessary in the evolution of human monogamous pair bonding. Organogenesis The earlobe, as a body part built of epithelium and connective tissue, might appear to be derived from dermatome. But this is not the case, as in the surround ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenylthiocarbamide
Phenylthiocarbamide (PTC), also known as phenylthiourea (PTU), is an organosulfur thiourea containing a phenyl ring. It has the unusual property that it either tastes very bitter or is virtually tasteless, depending on the genetic makeup of the taster. The ability to taste PTC is often treated as a dominant genetic trait, although inheritance and expression of this trait are somewhat more complex. PTC also inhibits melanogenesis and is used to grow transparent fish. About 70% of people can taste PTC, varying from a low of 58% for Indigenous Australians and indigenous peoples of New Guinea to 98% for indigenous peoples of the Americas. One study has found that non-smokers and those not habituated to coffee or tea have a statistically higher percentage of tasting PTC than the general population. PTC does not occur in food, but related chemicals do, and food choice can be related to a person's ability to taste PTC. History The tested genetic taste phenomenon of PTC w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimple
A dimple, also called a gelasin (, ), and a fovea buccalis, is a small natural indentation in the flesh on a part of the human body, most notably in the cheek. Numerous cultures believe that cheek dimples are a good luck charm that entices people who perceive them as physically attractive, but they are also associated with heroism and innocence, which has been included in literature for many centuries. Medical research debates whether cheek dimples can be inherited or which type of allele they are, but it is certain that humans with cheek dimples are more likely to have them in both cheeks. Depth and length appearances are affected by the shape of the skull and dimples can appear and disappear due to age. There are four types of facial dimples, including cheek, and the cleft chin (sometimes nicknamed a "chin dimple"). Overview Cheek dimples when present, show up when a person makes a facial expression, such as smiling, whereas a chin dimple is a small line on the chin that stay ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
