In Mendelian inheritance Mendelian inheritance is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their offspring; it underlies much of genetics. They were initially derived from the work of Gregor Mendel published in 1865 and 1866 which was "re-discovered" in 1900, and were initially very controversial, several dominant genes from either parent usually present with the dominant form of the trait. Only those that received the recessive gene from both Zygosity refers to the similarity of genes for a trait in an organism. If both genes are the same, the organism is homozygous for the trait. If both genes are different, the organism is heterozygous for that trait. If one gene is missing, it is hemizygous, and if both genes are missing, it is nullizygous parents present with the recessive phenotype A phenotype is any observable characteristic or trait of an organism: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior . Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and the interactions between the two.
This mode of inheritance implies that the child of two parents that display the "recessive" genotype should also display the "recessive" phenotype.
Cheek dimples Dimples are visible indentations of the skin, caused by underlying flesh, which form on some people's cheeks, especially when they smile . Dimples are genetically inherited and are a dominant trait. Dimples are usually found on both cheeks. A rarer form is the single dimple, which occurs on one side of the face only. Anatomically, dimples may be are a dominant phenotype. Attached earlobes The earlobe is composed of tough areolar and adipose connective tissues, lacking the firmness and elasticity of the rest of the pinna. Since the earlobe does not contain cartilage the earlobe has a large blood supply and may help to warm the ears and maintain balance but generally earlobes are not considered to have any major biological function are a recessive phenotype. Hitchhiker's thumbsIt also means the "recessive" phenotype may theoretically skip any number of generations, lying dormant in heterozygous Zygosity refers to the similarity of genes for a trait in an organism. If both genes are the same, the organism is homozygous for the trait. If both genes are different, the organism is heterozygous for that trait. If one gene is missing, it is hemizygous, and if both genes are missing, it is nullizygous individuals until they have children with someone who also has the recessive gene and both pass it on to their child.
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Examples
These traits include:
- Ability to taste Taste is a form of direct chemoreception and is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons. In humans and many other vertebrate animals the sense of taste partners with the less direct sense of smell, in the brain's perception of flavor. In the West, phenylthiocarbamide Phenylthiocarbamide, also known as PTC, or phenylthiourea, is an organic compound that either tastes very bitter or is virtually tasteless, depending on the genetic makeup of the taster. The ability to taste PTC is a dominant genetic trait. The test to determine PTC sensitivity is one of the most common genetic tests on humans
- Albinism Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin. Albinism results from inheritance of recessive gene alleles and is known to affect all vertebrates, including humans. The most common term used for an (recessive)
- Blood type A blood type is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system. Some of these antigens are also present on the surface of other types of cells of
- Brachydactyly Brachydactyly , is a medical term which literally means "shortness of the fingers and toes" (digits). The shortness is relative to the length of other long bones and other parts of the body. Brachydactyly is an inherited, usually dominant trait. It most often occurs as an isolated dysmelia, but can also occur with other anomalies as part (Shortness of fingers and toes)
- Cleft chin Categories: Congenital disorders | Genetics | Facial features (dominant)
- Cheek dimples Dimples are visible indentations of the skin, caused by underlying flesh, which form on some people's cheeks, especially when they smile . Dimples are genetically inherited and are a dominant trait. Dimples are usually found on both cheeks. A rarer form is the single dimple, which occurs on one side of the face only. Anatomically, dimples may be (dominant)
- Free (dominant) or attached (recessive) earlobes The earlobe is composed of tough areolar and adipose connective tissues, lacking the firmness and elasticity of the rest of the pinna. Since the earlobe does not contain cartilage the earlobe has a large blood supply and may help to warm the ears and maintain balance but generally earlobes are not considered to have any major biological function
- Wet (dominant) or dry (recessive) earwax Earwax, also known by the medical term cerumen, is a yellowish waxy substance secreted in the ear canal of humans and many other mammals. It protects the skin of the human ear canal, assists in cleaning and lubrication, and also provides some protection from bacteria, fungi, insects and water. Excess or impacted cerumen can press against the
- Face freckles Freckles are clusters of concentrated melanin which are most often visible on people with a fair complexion. A freckle is also called an "ephelis" (dominant)
- Hitchhiker's thumb The thumb is the first digit of the hand. When a person is standing in the medical anatomical position , the thumb is the lateral-most digit. The Medical Latin English adjective for thumb is pollical (recessive)
- Sexdactyly Polydactyly or polydactylism (from Ancient Greek πολύς "many" + δάκτυλος (daktulos) "finger"), also known as hyperdactyly, is a congenital physical anomaly in humans having supernumerary fingers or toes. When each hand or foot has six digits, it is sometimes called sexdactyly, hexadactyly, or hexadactylism (Six fingers/toes)
- Sickle-cell trait Sickle cell trait describes a condition in which a person has one abnormal allele of the hemoglobin beta gene (is heterozygous), but does not display the severe symptoms of sickle cell disease that occur in a person who has two copies of that allele (is homozygous). Sickle cell disease is a blood disorder in which the body produces an abnormal (also considered co-dominant)
- Widow's peak A widow's peak is a descending V-shaped point in the middle of the hairline (above the forehead). It is an example of a dominant inherited trait. The term comes from English folklore, where it was believed that this hair formation was a sign of a woman who would outlive her husband (dominant)
Traits previously believed to be Mendelian
Some traits were previously believed to be Mendelian, but their inheritance is (probably) based on more complex genetic models[citation needed], possibly involving more than one gene Inheritance of quantitative traits or polygenic inheritance refers to the inheritance of a phenotypic characteristic that varies in degree and can be attributed to the interactions between two or more genes and their environment. Though not necessarily genes themselves, quantitative trait loci are stretches of DNA that are closely linked to the. These include:
- Eye color Eye color is a polygenic phenotypic character and is determined by the amount and type of pigments in the eye's iris. Humans and other animals have many phenotypic variations in eye color, as blue, brown, gray, green and others. These variations constitute phenotypic traits
- Hair color Hair color is the pigmentation of hair follicles due to two types of melanin, eumelanin and pheomelanin. Generally, if more melanin is present, the color of the hair is darker; if less melanin is present, the hair is lighter. Levels of melanin can vary over time causing a person's hair color to change, and it is possible to have hair follicles of
- Morton's toe Morton's toe is the common term for the condition of a shortened first metatarsal in relation to the second metatarsal. It is a type of brachymetatarsia. This promotes an anterior position of the second metatarsal-phalangeal (MTP) joint in relation to the hallux (big toe). The condition may or may not result in the second toe (second from
- Tongue rolling The tongue is a group of muscles on the floor of the mouth that manipulates food for mastication. It is the primary organ of taste, as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly supplied with nerves and blood vessels. In humans a secondary function of the
See also
- Heritability Heritability is the proportion of phenotypic variation in a population that is attributable to genetic variation among individuals. Phenotypic variation among individuals may be due to genetic and/or environmental factors. Heritability analyses estimate the relative contributions of differences in genetic and non-genetic factors to the total
- Human genetic variation Human genetic variation is the genetic diversity of humans and represents the total amount of genetic characteristics observed within the human species. Genetic differences are observed between humans at both the individual and the population level. There may be multiple variants of any given gene in the human population , leading to polymorphism
- Human genetic clustering Human genetic clustering data can be used to infer population structure and assign individuals to groups that often correspond with their self-identified geographical ancestry. Recently, Lynn Jorde and Steven Wooding argued that "Analysis of many loci now yields reasonably accurate estimates of genetic similarity among individuals, rather
External links
Categories: Genetics
Thu, 08 Oct 2009 22:55:19 PDT
Music video by Ne-Yo performing Part Of The List. (C) 2009 The Island Def Jam Music Group. youtube.com.
