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48-661: Relaunch was a gray horse bred in Kentucky by Three Chimneys Farm & Taylor Made Farms. During his racing career he was owned by Glen Hill Farm and trained by John H. Adams . Relaunch won five of his eighteen starts, including the Del Mar Derby and the La Jolla Handicap in 1979. Relaunch is best remembered as a sire at Wimbledon Farm in Lexington, Kentucky . Relaunch was the sire of: Relaunch

96-410: A depigmentation pattern. It is a dominant allele , and thus a horse needs only one copy of the gray allele , that is, heterozygous , to be gray in color. A homozygous gray horse, one carrying two gray alleles, will always produce gray foals. Gray is common in many breeds. Today, about one horse in 10 carries the mutation for graying with age. The vast majority of Lipizzaners are gray, as are

144-575: A racehorse is a stub . You can help Misplaced Pages by expanding it . Gray (horse) A gray horse (or grey horse ) has a coat color characterized by progressive depigmentation of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike some equine dilution genes and some other genes that lead to depigmentation, gray does not affect skin or eye color. Gray horses may be born any base color, depending on other color genes present. White hairs begin to appear at or shortly after birth and become progressively more prevalent as

192-401: A roan or a rabicano . Some heavily fleabitten grays may also be confused with roans. However, roans are easily distinguishable from grays: roan consists of individual white hairs on a dark base coat, usually with the head and legs of the horse darker than the rest of the body. Rabicanos also have intermixed white hairs primarily on the body with a dark head. With gray horses, the head is often

240-450: A roan with more uniform intermixing of light and dark hairs. As they age, some gray horses, particularly those heterozygous for the gray gene, may develop pigmented speckles in addition to a white coat, a pattern colloquially called a "fleabitten gray." Gray horses appear in many breeds, though the color is most commonly seen in breeds descended from Arabian ancestors. Some breeds that have large numbers of gray-colored horses include

288-457: A skeletal muscle developmental deficit. In population genetics , the concept of heterozygosity is commonly extended to refer to the population as a whole, i.e., the fraction of individuals in a population that are heterozygous for a particular locus. It can also refer to the fraction of loci within an individual that are heterozygous. In an admixed population , whose members derive ancestry from two or more separate sources, its heterozygosity

336-433: A common ancestor that lived at least two thousand years ago. The discovery that gray can be linked to a single animal provides an example of how humans have "cherry-picked" attractive mutations in domestic animals. Gray is controlled by a single dominant allele of a gene that regulates specific kinds of stem cells . Homozygous grays turn white faster, are more likely to develop melanomas, and are less prone to develop

384-556: A diploid organism is hemizygous when only one copy is present. The cell or organism is called a hemizygote . Hemizygosity is also observed when one copy of a gene is deleted, or, in the heterogametic sex , when a gene is located on a sex chromosome. Hemizygosity is not the same as haploinsufficiency , which describes a mechanism for producing a phenotype. For organisms in which the male is heterogametic, such as humans, almost all X-linked genes are hemizygous in males with normal chromosomes, because they have only one X chromosome and few of

432-432: A genotype consisting of only a single copy of a particular gene in an otherwise diploid organism, and nullizygous refers to an otherwise-diploid organism in which both copies of the gene are missing. A cell is said to be homozygous for a particular gene when identical alleles of the gene are present on both homologous chromosomes . An individual that is homozygous-dominant for a particular trait carries two copies of

480-439: A gray horse as "white". However, most white horses have pink skin and some have blue eyes. A horse with dark skin and dark eyes under a white hair coat is gray. However, a gray horse with an underlying homozygous cream base coat color may be born with rosy-pink skin, blue eyes and near-white hair. In such cases, DNA testing may clarify the genetics of the horse. Some grays in intermediate stages of graying may be confused with

528-439: A gray horse is homozygous (GG), meaning that it has a gray allele from both parents, it will always produce gray offspring no matter the color genetics of the other parent. However, if a gray horse is heterozygous (Gg), meaning it inherits one copy of the recessive gene (g), that animal may produce offspring who are not gray, depending on the genetics of the other parent and Mendelian inheritance principles . Genetic testing

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576-418: A heterozygote will express only the trait coded by the dominant allele, and the trait coded by the recessive allele will not be present. In more complex dominance schemes the results of heterozygosity can be more complex. A heterozygous genotype can have a higher relative fitness than either the homozygous-dominant or homozygous-recessive genotype – this is called a heterozygote advantage . A chromosome in

624-547: A horse who has papers saying it is "gray" when the horse in front of them appears white. To further complicate matters, the skin and eyes may be other colors if influenced by other factors such as white markings , certain white spotting patterns or dilution genes . The gray gene (G) is an autosomal dominant gene . In simple terms, a horse which has even one copy of the gray allele , regardless of other coat color genes present, will always become gray. This also means that all gray horses must have at least one gray parent. If

672-402: A population: where n {\displaystyle n} is the number of individuals in the population, and a i 1 , a i 2 {\displaystyle a_{i1},a_{i2}} are the alleles of individual i {\displaystyle i} at the target locus. where m {\displaystyle m} is the number of alleles at

720-505: A single oocyte which subsequently splits into two morula . Zygosity is an important factor in human medicine. If one copy of an essential gene is mutated, the (heterozygous) carrier is usually healthy. However, more than 1,000 human genes appear to require both copies, that is, a single copy is insufficient for health. This is called haploinsufficiency . For instance, a single copy of the Kmt5b gene leads to haploinsufficiency and results in

768-400: A specific genotype. Heterozygous genotypes are represented by an uppercase letter (representing the dominant/wild-type allele) and a lowercase letter (representing the recessive/mutant allele), as in "Rr" or "Ss". Alternatively, a heterozygote for gene "R" is assumed to be "Rr". The uppercase letter is usually written first. If the trait in question is determined by simple (complete) dominance,

816-419: Is homozygous-recessive for a particular trait carries two copies of the allele that codes for the recessive trait . This allele, often called the "recessive allele", is usually represented by the lowercase form of the letter used for the corresponding dominant trait (such as, with reference to the example above, "p" for the recessive allele producing white flowers in pea plants). The genotype of an organism that

864-462: Is nullizygous . The DNA sequence of a gene often varies from one individual to another. These gene variants are called alleles . While some genes have only one allele because there is low variation, others have only one allele because deviation from that allele can be harmful or fatal. But most genes have two or more alleles. The frequency of different alleles varies throughout the population. Some genes may have alleles with equal distributions. Often,

912-525: Is from the Greek zygotos "yoked," from zygon "yoke") ( / z aɪ ˈ ɡ ɒ s ɪ t i / ) is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Most eukaryotes have two matching sets of chromosomes ; that is, they are diploid . Diploid organisms have the same loci on each of their two sets of homologous chromosomes except that

960-406: Is homozygous-recessive for a particular trait is represented by a doubling of the appropriate letter, such as "pp". A diploid organism is heterozygous at a gene locus when its cells contain two different alleles (one wild-type allele and one mutant allele) of a gene. The cell or organism is called a heterozygote specifically for the allele in question, and therefore, heterozygosity refers to

1008-441: Is how to discern a gray horse from a white horse . White horses usually have pink skin and sometimes even have blue eyes. Young horses with hair coats consisting of a mixture of colored and gray or white hairs are sometimes confused with roan . Some horses that carry dilution genes may also be confused with white or gray. While gray is classified as a coat color by breed registries , genetically it may be more correct to call it

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1056-595: Is irrelevant for them. As discussed above, "zygosity" can be used in the context of a specific genetic locus (example ). The word zygosity may also be used to describe the genetic similarity or dissimilarity of twins. Identical twins are monozygotic , meaning that they develop from one zygote that splits and forms two embryos. Fraternal twins are dizygotic because they develop from two separate oocytes (egg cells) that are fertilized by two separate sperm . Sesquizygotic twins are halfway between monozygotic and dizygotic and are believed to arise after two sperm fertilize

1104-476: Is known as being "identical by state", or IBS. Because the alleles of autozygous genotypes come from the same source, they are always homozygous, but allozygous genotypes may be homozygous too. Heterozygous genotypes are often, but not necessarily, allozygous because different alleles may have arisen by mutation some time after a common origin. Hemizygous and nullizygous genotypes do not contain enough alleles to allow for comparison of sources, so this classification

1152-508: Is now possible to determine whether a horse is homozygous or heterozygous for gray. The gray gene does not affect skin or eye color, so grays typically have dark skin and eyes, as opposed to the unpigmented pink skin of white horses . In 2008, researchers at Uppsala University in Sweden identified the genetic mutation that governs the graying process. The study revealed that all gray horses carry an identical mutation that can be traced back to

1200-597: Is proven to be at least as great as the least heterozygous source population and potentially more than the heterozygosity of all the source populations. It reflects the contributions of its multiple ancestral groups. Admixed populations show high levels of genetic variation due to the fusion of source populations with different genetic variants. Typically, the observed ( H o {\displaystyle H_{o}} ) and expected ( H e {\displaystyle H_{e}} ) heterozygosities are compared, defined as follows for diploid individuals in

1248-498: The Chinese hamster ovary cell line, a number of genetic loci are present in a functional hemizygous state, due to mutations or deletions in the other alleles. A nullizygous organism carries two mutant alleles for the same gene. The mutant alleles are both complete loss-of-function or 'null' alleles, so homozygous null and nullizygous are synonymous. The mutant cell or organism is called a nullizygote . Zygosity may also refer to

1296-840: The Thoroughbred , the Arabian , the American Quarter Horse and the Welsh pony . Breeds with a very high prevalence of gray include the Percheron , the Andalusian , and the Lipizzaner . People who are unfamiliar with horses may refer to gray horses as "white". However, a gray horse whose hair coat is completely "white" will still have black skin (except under markings that were white at birth) and dark eyes. This

1344-431: The pearl gene or "barlink factor", may also create very light-coated horses. Similarly, the champagne gene can lighten coat color, often producing dappling or light colors that can be confused with gray. In spite of its name, the silver dapple gene has nothing to do with graying. It is a dilution gene that acts only on a black coat, diluting the coat to a dark brown and the mane to a flaxen shade. Horses that express

1392-412: The "fleabitten" speckling than heterozygous grays. Researchers suggest the pigmented speckles of the "fleabitten" gray, as well as more intense reddish-brown colored areas called "blood" markings, may be caused by a loss or inactivation of the gray allele in some of the somatic cells as that would explain why the speckles are more common on heterozygous grays than homozygotes. The identification of

1440-486: The Appaloosa and are seldom seen elsewhere. The dilution genes that create dun, cream, pearl, silver dapple and champagne coloring may occasionally result in confusion with gray. Some horses with a particular type of dun hair coat known as a "blue dun", grullo , or "mouse" dun appear to be a solid gray. However, this color is caused by the dun gene acting on a black base coat, and horses who are dun have all hairs

1488-411: The age of a horse except in the broadest of terms: a very young horse will never have a white coat (unless it is a true white horse ), while a horse in its teens usually is completely grayed out. One must also be careful not to confuse the small amount of gray hairs that may appear on some older horses in their late teens or twenties, which do not reflect the gray gene and never cause a complete graying of

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1536-561: The age of one year. Over time, white hairs replace the birth color. The changing patterns of white and dark hairs have many informal names, such as "rose gray," "salt and pepper," "iron gray", or "dapple gray." As the horse ages, the coat continues to lighten, often to a pure white. Some horses develop pigmented reddish-brown speckles on an otherwise white hair coat. Such horses are often called "fleabitten gray". Different breeds, and individuals within each breed, take differing amounts of time to gray out. Thus, graying cannot be used to approximate

1584-448: The allele that codes for the dominant trait . This allele, often called the "dominant allele", is normally represented by the uppercase form of the letter used for the corresponding recessive trait (such as "P" for the dominant allele producing purple flowers in pea plants). When an organism is homozygous-dominant for a particular trait, its genotype is represented by a doubling of the symbol for that trait, such as "PP". An individual that

1632-406: The contrast of the markings of these patterns, sometimes colloquially described as "ghosting." A gray foal may be born any color. However, bay , chestnut , or black base colors are most often seen. As the horse matures, it "grays out" as white hairs begin to replace the base or birth color. Usually white hairs are first seen by the muzzle, eyes and flanks, occasionally at birth, and usually by

1680-474: The different variations in the genes do not affect the normal functioning of the organism at all. For some genes, one allele may be common, and another allele may be rare. Sometimes, one allele is a disease -causing variation while another allele is healthy. In diploid organisms, one allele is inherited from the male parent and one from the female parent. Zygosity is a description of whether those two alleles have identical or different DNA sequences. In some cases

1728-481: The first area to lighten, especially around the eyes and muzzle. Also, roans do not lighten with age, while grays always do. The varnish roan is another unusual coloration, sometimes seen in Appaloosa horses, that, like gray, can change with age, but unlike gray, the horse does not become progressively lighter until it is pure white. Varnish roans are created by the action of leopard complex within breeds such as

1776-467: The gray mutation is of great interest in of medical research since this mutation also enhances the risk for melanoma in horses: some studies have suggested as many as 80% of grays over 15 years of age have some form of melanoma. Growth rate depends on the type, and many are slow-growing, but over time, many develop into a malignant melanoma . The study of gray genetics has pointed to a molecular pathway that may lead to tumour development. Both STX17 and

1824-400: The horse ages as white hairs become intermingled with hairs of other colors. Graying can occur at different rates—very quickly on one horse and very slowly on another. As adults, most gray horses eventually become completely white, though some retain intermixed light and dark hairs. The stages of graying vary widely. Some horses develop a dappled pattern for a period of time, others resemble

1872-404: The horse. This change in hair color means that the same gray horse will appear to be a different color over time, sometimes resulting in a need to change the color noted on breed registry papers. Other times, people traveling with gray horses who have a pure white hair coat have encountered problems with non-horse-oriented officials such as police officers or border guards who are unclear about

1920-575: The majority of Andalusian horses . Many breeds of French draft horse such as the Percheron and Boulonnais are often gray as well. Gray is also found among Welsh Ponies , Thoroughbreds , and American Quarter Horses . All of these breeds have common ancestry in the Arabian horse . In particular, all gray Thoroughbreds descend from a horse named Alcock's Arabian , a gray born in 1700. The gray coat color makes up about 3% of Thoroughbreds. Gray also affects spotting patterns of pintos and leopard complex horses such as Appaloosas . Its effects wash out

1968-596: The neighboring NR4A3 gene are overexpressed in melanomas from gray horses, and those carrying a loss-of-function mutation in ASIP (agouti signaling protein) had a higher incidence of melanoma, implying that increased melanocortin-1 receptor signaling promotes melanoma development in Gray horses. Some studies indicate as many as 66% of melanomas become malignant, though other studies have found much lower rates, and in one case, zero. Many people who are unfamiliar with horses refer to

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2016-400: The origin(s) of the alleles in a genotype. When the two alleles at a locus originate from a common ancestor by way of nonrandom mating ( inbreeding ), the genotype is said to be autozygous . This is also known as being "identical by descent", or IBD. When the two alleles come from different sources (at least to the extent that the descent can be traced), the genotype is called allozygous . This

2064-410: The same color; there is no intermingling of white and dark hairs. Also, dun horses do not get lighter as they age. Horses that are a light cream color are also not grays. These are usually cremello, perlino or smoky cream horses, all colors produced by the action of the cream gene . However, if a gray parent passes on the gene, the hairs will turn white like any other gray. Another cream-colored dilution,

2112-459: The same genes are on the Y chromosome . Transgenic mice generated through exogenous DNA microinjection of an embryo's pronucleus are also considered to be hemizygous, because the introduced allele is expected to be incorporated into only one copy of any locus. A transgenic individual can later be bred to homozygosity and maintained as an inbred line to reduce the need to confirm the genotype of each individual. In cultured mammalian cells, such as

2160-431: The sequences at these loci may differ between the two chromosomes in a matching pair and that a few chromosomes may be mismatched as part of a chromosomal sex-determination system . If both alleles of a diploid organism are the same, the organism is homozygous at that locus. If they are different, the organism is heterozygous at that locus. If one allele is missing, it is hemizygous , and, if both alleles are missing, it

2208-583: The silver dapple gene (and do not have the gray gene) are born that color and it will not lighten. However, again, if one parent passes on the gray gene, the gray gene will again be dominant. Throughout history, both gray and white horses have been mythologized. As part of its legendary dimension, the gray horse in myth has been depicted with seven heads ( Uchaishravas ) or eight feet ( Sleipnir ), sometimes in groups or singly. There are also mythological tales of divinatory gray horses who prophesy or warn of danger. Homozygous Zygosity (the noun, zygote ,

2256-460: The term "zygosity" is used in the context of a single chromosome. The words homozygous , heterozygous , and hemizygous are used to describe the genotype of a diploid organism at a single locus on the DNA. Homozygous describes a genotype consisting of two identical alleles at a given locus, heterozygous describes a genotype consisting of two different alleles at a locus, hemizygous describes

2304-473: Was also the grandsire of Hall of Fame inductee Tiznow and damsire of Ghostzapper , the 2004 World's Top Ranked Horse , as well as the damsire of Real Shadai , the 1993 Leading sire in Japan . Relaunch died on November 5, 1996, of colic . * Relaunch is inbred 4S × 4S to the stallion War Relic , meaning that he appears twice fourth generation on the sire side of his pedigree. This article about

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