| Hair whorl | |
|---|---|
 Human baby hair whorl | |
| Details | |
| Identifiers | |
| Latin | vortices pilorum |
| TA98 | A16.0.00.026 |
| FMA | 76564 |
| Anatomical terminology | |
A hair whorl 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. Hair whorls, also known as crowns, swirls, or trichoglyphs, can be either clockwise or counterclockwise in direction of growth.
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. [1] However, Klar's research methodology in this and other studies has been questioned. [2]
The direction of hair whorl is not consistent with Blaschko's lines. [3]
Another result concerning handedness of the progeny of discordant monozygotic twins suggests that left handed people are one gene apart from right handed people. Together, these results suggest (1) that a single gene controls handedness, whorl orientation, and twin concordance and discordance and (2) that neuronal and visceral (internal organs) forms of bilateral asymmetry are coded by separate sets of genetic pathways. [4]
There are many (mostly apocryphal) theories concerning horse behavior and their hair whorls. [5]
One paper has suggested that abnormal hair whorls can be used to assess the likelihood of agitated behavior or temperament in cattle in the auction ring. [6]
An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosomal pairs, which may have different structures. The DNA in autosomes is collectively known as atDNA or auDNA.
Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fine vellus hair. Most common interest in hair is focused on hair growth, hair types, and hair care, but hair is also an important biomaterial primarily composed of protein, notably alpha-keratin.
Body relative directions are geometrical orientations relative to a body such as a human person's. The most common ones are: left and right; forward(s) and backward(s); up and down. They form three pairs of orthogonal axes.
In human biology, handedness is an individual's preferential use of one hand, known as the dominant hand, due to it being stronger, faster or more dextrous. The other hand, comparatively often the weaker, less dextrous or simply less subjectively preferred, is called the non-dominant hand. In a study from 1975 on 7688 children in US grades 1-6, Left handers comprised 9.6% of the sample, with 10.5% of male children and 8.7% of female children being left-handed. Handedness is often defined by one's writing hand, as it is fairly common for people to prefer to do a particular task with a particular hand. There are examples of true ambidexterity, but it is rare—most people prefer using one hand for most purposes.
Roan is a coat color found in many animals, including horses, cattle, antelope, cat and dogs. It is defined generally as an even mixture of white and pigmented hairs that do not "gray out" or fade as the animal ages. There are a variety of genetic conditions which produce the colors described as "roan" in various species.
Melanesians are the predominant and indigenous inhabitants of Melanesia, in a wide area from New Guinea to the Fiji Islands. Most speak either one of the many languages of the Austronesian language family, especially ones in the Oceanic branch, or from one of the many unrelated families of Papuan languages. Other languages are the several creoles of the region, such as Tok Pisin, Hiri Motu, Solomon Islands Pijin, Bislama, and Papuan Malay.
Hypertrichosis is an abnormal amount of hair growth over the body. The two distinct types of hypertrichosis are generalized hypertrichosis, which occurs over the entire body, and localized hypertrichosis, which is restricted to a certain area. Hypertrichosis can be either congenital or acquired later in life. The excess growth of hair occurs in areas of the skin with the exception of androgen-dependent hair of the pubic area, face, and axillary regions.
Blaschko's lines, also called the lines of Blaschko, are lines of normal cell development in the skin. These lines are only visible in those with a mosaic skin condition or in chimeras where different cell lines contain different genes. These lines may express different amounts of melanin, or become visible due to a differing susceptibility to disease. In such individuals, they can become apparent as whorls, patches, streaks or lines in a linear or segmental distribution over the skin. They follow a V shape over the back, S-shaped whirls over the chest and sides, and wavy shapes on the head. Not all mosaic skin conditions follow Blaschko's lines.
Body hair, or androgenic hair, is the terminal hair that develops on the human body during and after puberty. It is differentiated from the head hair and less visible vellus hair, which is much finer and lighter in color. The growth of androgenic hair is related to the level of androgens and the density of androgen receptors in the dermal papillae. Both must reach a threshold for the proliferation of hair follicle cells.
Black hair is the darkest and most common of all human hair colors globally, due to larger populations with this dominant trait. It is a dominant genetic trait, and it is found in people of all backgrounds and ethnicities. Black hair contains a large amount of eumelanin pigmentation, a type of melanin. This hair type contains a much more dense quantity of eumelanin in comparison to other hair colors, such as brown, blonde and red. In English, various types of black hair are sometimes described as soft-black, raven black, or jet-black. The range of skin colors associated with black hair is vast, ranging from the palest of light skin tones to dark skin. Black-haired humans can have dark or light eyes.
Genetics is the study of genes and tries to explain what they are and how they work. Genes are how living organisms inherit features or traits from their ancestors; for example, children usually look like their parents because they have inherited their parents' genes. Genetics tries to identify which traits are inherited and to explain how these traits are passed from generation to generation.
Uncombable hair syndrome (UHS) is a rare structural anomaly of the hair with a variable degree of effect. It is characterized by hair that is silvery, dry, frizzy, wiry, and impossible to comb. It was first reported in the early 20th century. It typically becomes apparent between the ages of 3 months and 12 years. UHS has several names, including "pili trianguli et canaliculi," "cheveux incoiffables," and "spun-glass hair." This disorder is believed to be autosomal recessive in most instances, but there are a few documented cases where multiple family members display the trait in an autosomal dominant fashion. Based on the current scientific studies related to the disorder, the three genes that have been causally linked to UHS are PADI3, TGM3, and TCHH. These genes encode proteins important for hair shaft formation. Clinical symptoms of the disorder arise between 3 months and 12 years of age. The quantity of hair on the head does not change, but hair starts to grow more slowly and becomes increasingly "uncombable." To be clinically apparent, 50% of all scalp hair shafts must be affected by UHS. This syndrome only affects the hair shaft of the scalp and does not influence hair growth in terms of quantity, textural feel, or appearance on the rest of the body.
Left-handedness always occurs at a lower frequency than right-handedness. Generally, left-handedness is found in 10.6% of the overall population. Some studies have reported that left-handedness is more common in twins than in singletons, occurring in 21% of people who are twins. However other studies did not find a higher left-handedness prevalence in twins compared to singletons.
A hair whorl is a patch of hair growing in the opposite direction of the rest of the hair. Hair whorls can occur on animals with hairy coats, and are often found on horses and cows. Locations where whorls are found in equines include the stomach, face, stifle and hocks. Hair whorls in horses are also known as crowns, swirls, trichoglyphs, or cowlicks.
Two-dimensional rotation can occur in two possible directions. Clockwise motion proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back up to the top. The opposite sense of rotation or revolution is anticlockwise (ACW) or counterclockwise (CCW).
A widow's peak is a V-shaped point in the hairline in the center of the forehead. Hair growth on the forehead is suppressed in a bilateral pair of periorbital fields. Without a widow's peak, these fields join in the middle of the forehead so as to give a hairline that runs straight across. A widow's peak results when the point of intersection on the forehead of the upper perimeters of these fields is lower than usual.
Midphalangeal hair, or the presence/absence of hair on the middle phalanx of the ring finger, is one of the most widely studied markers in classical genetics of human populations. Although this polymorphism was observed at other fingers as well, for this kind of research, the fourth finger of the hand has been conventionally selected.
Jeremy was a left-coiled garden snail investigated by biologists. The snail had a rare condition which caused its shell to coil to the left; in most snails the shell coils to the right. At first it was thought to be a rare genetic mutation, although later work revealed that it was likely due to an accident in early development.
Silvia Paracchini FRSE is a geneticist who researches the contribution of genetic variation to neurodevelopmental traits such as dyslexia and human handedness.
Amar Jit Singh Klar was an Indian-American yeast geneticist and epigenetics researcher. He received media attention for his research on the genetics of human traits, including handedness and the direction of hair whorls.
| Authority control: Scientific databases |
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