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42-628: Ceramic sculptures of a hairless breed of dog have been found in burial sites in ancient West Mexico. In ancient times, Xolos were often sacrificed and then buried with their owners to act as guides to the soul on its journey to the underworld . They have been found in burial sites of both the Maya and the Toltec. Sixteenth-century Spanish accounts tell of large numbers of dogs being served at banquets. Aztec merchant feasts could have 80–100 turkeys and 20–40 dogs served as food. When these two meats were served in

84-457: 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

126-515: A "cultural heritage and symbol" of Mexico City. The Dolores Olmedo Museum keeps a pack of Xolos on their grounds. The Xoloitzcuintle is the symbol and mascot of Club Tijuana , the Xoloitzcuintles de Caliente, a professional soccer club founded in 2007. Xolos are depicted in some of Mexican artist Frida Kahlo 's paintings, one of which is commemorated on the 2007 500- peso note, featuring Frida Kahlo's painting titled The Love Embrace of

168-738: A common origin. Hemizygous and nullizygous genotypes do not contain enough alleles to allow for comparison of sources, so this classification 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

210-467: A decade, the FCI realized that the breed would become extinct if drastic action were not taken to save it. This led to the widely publicized Xolo Expedition of 1954. With the official sanction of the FCI, Wright and a team of Mexican and British dog authorities set off to discover if any purebred Xolos still existed in remote areas of Mexico. Eventually 10 structurally strong Xolos were found and these dogs formed

252-407: A given locus, heterozygous describes a genotype consisting of two different alleles at a locus, hemizygous describes 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

294-409: 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 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

336-402: 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

378-962: A range of sizes, which breeders have standardized into three designations: Standard, Miniature and Toy. The Xoloitzcuintle has a calm and attentive temperament. The Xolo has been developed by natural selection for thousands of years, and is therefore generally not prone to health and structure problems as other dog breeds more modified by human selection efforts. Xolos came from tropical climates and are not suited for outdoor life in colder temperate and northern climates; they should be considered an indoor dog breed. They need bathing, light grooming and skin care as with other dogs of similar physical type, or acne can result. Most skin problems arise from poor breeding, neglect, or over-bathing and over-lotioning, stripping natural protections and clogging pores. Xoloitzcuintles are represented in popular culture and are popular pets. Museo El Carmen in Mexico City exhibited

420-630: A show titled Xolos, compañeros de viaje (Xolos, travel companions) in 2019–20 of more than 100 artifacts – ceramics, remains, and artworks – overviewing the importance of the Xoloitzcuintle in Mexican heritage. A Xolo named Dante stars in the US blockbuster CGI animation 2017 Disney / Pixar film Coco . On August 12, 2016, the Mayor of Mexico City Miguel Ángel Mancera designated the Xoloitzcuintle

462-505: 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

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504-414: A spontaneous mutation thousands of years ago. The recessive expression of the trait will produce a coated variety, which is genetically inseparable from the hairless, as the homozygous appearance of the hairless mutation is fatal to the unborn pup. Most litters contain both hairless and coated puppies. The coated variety, covered with a short, flat dense coat represents the original form of the dog, prior to

546-411: Is called a heterozygote specifically for the allele in question, and therefore, heterozygosity refers to 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

588-406: Is called a heterozygote advantage . A chromosome in 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

630-453: 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 the Chinese hamster ovary cell line, a number of genetic loci are present in a functional hemizygous state, due to mutations or deletions in

672-452: 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 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

714-454: Is missing, it is hemizygous , and, if both alleles are missing, it 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

756-597: 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

798-460: Is usually written first. If the trait in question is determined by simple (complete) dominance, 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

840-510: The Chihuahua and Xoloitzcuintli derive 4% and 3% of their ancestry from pre-colonial dogs, almost entirely being descended from Eurasian dogs. Their phenotype is a consequence of canine ectodermal dysplasia caused by a mutation on the FOXI3 autosomal gene. The breed did not receive any official notice in its homeland until the 1950s. The FCI , founded in 1940, was not prepared to declare

882-646: The Universe, the Earth (Mexico), Myself, Diego, and Señor Xolotl (1949) on the reverse of the note. Diego Rivera 's large murals, The History of Mexico , in the Palacio Nacional in Mexico City feature numerous Xolos. Underworld The underworld , also known as the netherworld or hell , is the supernatural world of the dead in various religious traditions and myths , located below

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924-506: The XCA has compiled a stud book modeled on requirements for eventual AKC acceptance, held an annual independent specialty show, published a quarterly newsletter, The Xolo News , and maintained an active national rescue network, National Xolo Rescue (known before 2009 as The Xolo Rescue League). Since January 1, 2007, FSS registered Xolos have been eligible to compete in AKC performance events. The breed

966-520: The Xolo an official purebred at that time. According to breed historian Norman Pelham Wright, author of The Enigma of the Xoloitzcuintli , Xolos began to turn up at Mexican dog shows in the late 1940s. Although they were recognized as indigenous specimens of a native breed, interest in them was minimal at that time, because information was scarce and no standard existed by which to judge them. Within

1008-626: The breed's only AKC champion to date. He earned his title on October 19, 1940. In 1959, the Xolo was dropped from the AKC stud book due to the breed's scarcity and perceived extinction . The Xoloitzcuintli Club of America (XCA), the official parent club for the breed, was founded on October 26, 1986, to regain AKC recognition for the breed. On May 13, 2008, AKC voted to readmit the breed to its Miscellaneous Class starting January 1, 2009. The founding members voted unanimously to recognize all three sizes (toy, miniature and standard) and both varieties (hairless and coated) at their initial meeting. Since then,

1050-426: The dogs of the coated variety have complete dentition. The Xolo is moderate in all aspects of its appearance, conveying an impression of strength, agility, and elegance. Xolo body proportions are rectangular, slightly longer in total body length than the height measured at the highest point of the withers (top of the shoulders). The breed occurs naturally in two varieties, hairless and coated. Hairless Xolos result from

1092-528: The entire genome indicated that domesticated dogs entered North America from Siberia for 4,500 years and were isolated for the next 9,000 years. After contact with Europeans, these dogs were replaced by Eurasian dogs and their local descendants. The pre-contact dogs exhibited a unique genetic signature that is now almost gone due to their assimilation into the Eurasian dog gene pool. In 2020, the sequencing of ancient dog genome indicates that in two Mexican breeds

1134-417: The example above, "p" for the recessive allele producing white flowers in pea plants). The genotype of an organism that 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

1176-469: The female parent. Zygosity is a description of whether those two alleles have identical or different DNA sequences. In some cases 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

1218-574: The foundation of Mexico's program to revive the breed. A committee headed by Wright authored the first official standard for the breed; on May 1, 1956, the Xolo was finally recognized in its native land and, as Mexico is a member of the FCI, worldwide. Xolos were among the first breeds recorded by the American Kennel Club (AKC). A Mexican dog named "Mee Too" made breed history as the first AKC-registered Xolo in 1887. "Chinito Junior", bred and owned by Valetska Radtke of New York City, became

1260-441: The gene are present on both homologous chromosomes . An individual that is homozygous-dominant for a particular trait carries two copies of 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

1302-582: 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 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

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1344-414: The occurrence of the spontaneous hairless mutation. The hairless variety is completely hairless on the body, with many dogs exhibiting a few short hairs on the top of the head, the toes, and the tip of the tail. Most hairless dogs are black or bluish-gray in color. The allele responsible for the Xolo's hairlessness also affects the dog's dentition: Hairless Xolos typically have an incomplete set of teeth while

1386-453: 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 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 ),

1428-420: The population. Some genes may have alleles with equal distributions. Often, 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

1470-506: The presence of the dominant allele (HH or Hh) at the FOXI3 locus. Coated Xolo are the recessive expression, occurring only when two coated alleles (hh) are present. Breeding coated to coated will only produce coated pups because only the coated allele is present to be passed on. Both varieties occur in all hair or skin colors, and the skin is often marked, splashed, or spotted. The most common colors are various shades termed black, grey, bronze, yellowish-blonde, blue and red. The breed occurs in

1512-444: The same loci on each of their two sets of homologous chromosomes except that 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

1554-462: The same dish, the dog meat was at the bottom of the dish, possibly because it was held in lower regard. The Aztecs consumed few domesticated animals, with over 90% of the bones found at archeological sites being deer. A 1999 genetic study using mitochondrial DNA found that the DNA sequences of the Xoloitzcuintle were identical to those of dogs from the Old World. In 2018, an analysis of DNA from

1596-592: The underworld in various religious traditions, with links to corresponding articles. Zygosity#Homozygous Zygosity (the noun, zygote , 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

1638-407: The underworld requires a proper observation of ceremony, such as the ancient Greek story of the recently dead Patroclus haunting Achilles until his body could be properly buried for this purpose. People with high social status were dressed and equipped in order to better navigate the underworld. A number of mythologies incorporate the concept of the soul of the deceased making its own journey to

1680-480: The underworld, with the dead needing to be taken across a defining obstacle such as a lake or a river to reach this destination. Imagery of such journeys can be found in both ancient and modern art. The descent to the underworld has been described as "the single most important myth for Modernist authors". This list includes underworlds in various religious traditions, with links to corresponding articles: Echeide , Guayota This list includes rulers or guardians of

1722-404: The world of the living. Chthonic is the technical adjective for things of the underworld. The concept of an underworld is found in almost every civilization and "may be as old as humanity itself". Common features of underworld myths are accounts of living people making journeys to the underworld , often for some heroic purpose. Other myths reinforce traditions that the entrance of souls to

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1764-676: Was moved into the AKC Studbook in December 2010 and has been eligible to be shown in the AKC Non-Sporting group since January 1, 2011. The breed ranges in size from about 10 to 55 lb (5 to 23 kg). The height is 9 to 26 inches (23–67 cm). Similar in appearance to a Pharaoh Hound , with a sleek body, almond-shaped eyes, large bat-like ears, and a long neck, the Xolo is notable for its dominant trait of hairlessness. The dominant hairless trait originated in this breed as

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