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The Mongolian gerbil or Mongolian jird (Meriones unguiculatus) is a small rodent belonging to the subfamilyGerbillinae. Body size is typically 110-135mm, with a 95-120mm tail, and body weight 60-130g, with adult males larger than females. The animal is used in science and kept as a small house pet. Their use in science dates back to the latter half of the 19th century, but they only started to be kept as pets after 1954, when they were brought to the United States. However, their use in scientific research has fallen out of favor.
Soil on the steppes is sandy and is covered with grasses, herbs, and shrubs. The steppes have cool, dry winters and hot summers. The temperature can get up to 50 °C (122 °F), but the average temperature for most of the year is around 20 °C (68 °F).
In the wild, these gerbils live in groups generally consisting of one parental pair, the most recent litter, and a few older pups. Only the dominant female will produce pups, but she will mate with multiple males while in estrus (heat). One group of gerbils generally ranges over 325-1,550 square metres (0.08-0.38 acres).
A group lives in a central burrow with 10-20 exits. Some deeper burrows with only one to three exits in their territory may exist. These deeper burrows are used to escape from predators when they are too far from the central burrow. A group's burrows often interconnect with other groups.
There's a popular misconception about the meaning of this scientific name, appearing both in printed works and in websites, due to the genus Meriones sharing the name with Greek warrior Meriones in Homer's Iliad; however, translations like "clawed warrior" are incorrect. The genus was named by Johann Karl Wilhelm Illiger in 1811, deriving from the Greek word (femur). Combined with 'unguiculate', meaning to have claws or nails in Latin, the name can be loosely translated as 'clawed femur'.
Gerbils only became popular pets after 1954, when 20 breeding pairs were brought to the United States from eastern Mongolia for scientific testing. Almost all pet gerbils today are descended from these 40. Gerbils were brought to the United Kingdom in 1964 from the United States.
Gerbils have a long history of use in scientific research, although nowadays they are rarely used. For example, in the United Kingdom in 2017, only around 300 Mongolian gerbils were used in experimental procedures, compared to over 2 million mice.
Most gerbils used in scientific research are derived from the Tumblebrook Farm strain, which has its origins in 20 pairs of wild-caught Mongolian gerbils sent to Japan in 1935. 11 of these animals were subsequently sent to Tumblebrook Farm in the USA, with additional animals later sent to Charles River Ltd in Italy in 1996.
Gerbils have a wide hearing range, from detection of low frequency foot drumming to higher frequency chirps and therefore may be a more suitable model of human hearing loss than mice and rats, which are high-frequency specialists.
10-20% of gerbils exhibit spontaneous epileptiform seizures, typically in response to a stressor such as handling or cage cleaning. Epilepsy in gerbils has a genetic basis, and seizure-prone and seizure-resistant lines have been bred.
Like other desert rodents such as fat sandrats, Mongolian gerbils are susceptible to diet-induced diabetes, although incidence is low. A diabetes-prone line has recently been generated, showing that gerbil diabetes has at least some genetic basis.
Genetics and genomics
Laboratory gerbils are derived from a small number of founders, and so genetic diversity was generally assumed to be low. Initial genetic studies based on small numbers of genetic markers appeared to support this, but more recent genome-wide Genotyping-by-Sequencing (GBS) data has shown that genetic diversity is actually quite high. It has been suggested that laboratory gerbils should be considered domesticated, and designated "M. unguiculatus forma domestica" to differentiate them from wild animals. A Mongolian gerbil genome sequence was published in 2018 and a genetic map comprising 22 linkage groups (one per chromosome) in 2019.
The Mongolian gerbil, a gentle and hardy animal, has become a popular small house pet. It was first brought from China to Paris in the 19th century, and became a popular house pet. It was later brought to the United States in 1954 by Dr. Victor Schwentker for use in research. Selective breeding for the pet trade has resulted in a wide range of different color and pattern varieties.
Mongolian gerbils prefer to live in pairs or groups rather than alone. They are social and gentle, and do not bite readily. As diggers and tunnel-makers they are better suited to a tank with a deep substrate or bedding rather than a hamster cage, since the absorbent substrate is liable to be kicked up and out of a cage pretty quickly.
Mongolian gerbils are also chewers and need plenty of cardboard items and chew toys; the cardboard will be chewed up into the bedding and mixed with the substrate. They do not need fresh food like vegetables and it can actually give them diarrhea; a diet based on one or more seeds, millet and alfalfapellet mix is sufficient.
Water should be provided with a drip-feed system to prevent an accidental build-up of harmful molds in the tank environment. Although gerbils are adapted to the desert, they require water to be supplied at all times to be safe and healthy. Care should be taken not to introduce new smells suddenly into the tank, because the tank is considered by the gerbils to be their territory. Gerbils are active and appreciate a running or exercise wheel. Repetitive corner digging can be minimized by providing tunnels while gerbils are in their young, formative months. As with most animals, they appreciate a secure, private area that is dark for sleeping.
Gerbils are prohibited as pets in some regions for being invasive, including California.
Currently recognized colour morphs and their genetic basis are described below.
Light Colourpoint Agouti
Golden Agouti - All Mongolian Gerbils in the wild are Golden Agouti, also called Agouti. The hair shafts on the back are grey at the base, gold in the middle and tipped with black, making an even mix of golden brown with black ticking. The belly is creamy white. An Agouti gerbil has black eyes.
Black - A Black gerbil is black both on its back and on its belly. It most often has a "bib" or white line running down its chin. It also may have some white on its paws. A Black gerbil has black eyes. It carries double recessive genes abbreviated "a" for Agouti.
Argente / Argente Golden - An Argente gerbil is orange with a creamy white belly. It has deep ruby eyes. If one were to brush back the fur on its back, one would see that the roots are grey. Argente gerbils carry double recessive genes for "Pink Eyed" which is abbreviated, "p" although the eye colour is ruby rather than pink.
Argente Cream - An Argente Cream gerbil is an Argente lightened by a Himalayan gene, c(h). It is light orange with a creamy white belly and ruby eyes. The undercoat is grey like the Argente Golden, but diluted due to the c(h).
Topaz - A Topaz gerbil is an Argente lightened by a gene called Chinchilla Medium, c(chm), formerly called Burmese, c(b). This colour is lighter than an Argente Golden but darker than an Argente Cream, and it often has slightly darker points at the ears, nose and tail. It has a creamy white belly and ruby eyes. The undercoat is grey, but diluted due to the c(chm). Also called "Argente Fawn."
Lilac - A Lilac gerbil is medium grey all over. It has ruby eyes and carries double recessives for both the "a" and "p" alleles.
Dove - A Dove gerbil is a Lilac lightened by the Himalayan gene, c(h). It is light grey all over. It has ruby eyes.
Sapphire - A Sapphire gerbil is a Lilac lightened by a gene called Chinchilla Medium, c(chm). This colour is lighter than a Lilac but darker than a Dove. It has ruby eyes.
Pink-eyed White - A Pink-eyed White gerbil is completely white with pink eyes.
Himalayan/Dark Tailed White - A Himalayan or Dark Tailed White gerbil is white with ruby eyes. After several months its tail will darken from white to a shade of light or dark grey depending on a variety of factors such as the temperature of the environment and the other recessive alleles it may carry. A gerbil that is Dark Tailed White, abbreviated "DTW," carries double recessives of the Himalayan gene, "c(h)."
Burmese - A Burmese gerbil is an all over chocolate colour. Around eight weeks or so, it will begin to develop darker points on the tail, nose, feet and tips of the ear. It often has a "bib" or white line running down the chin. It also may have some white on its paws. All Burmese gerbils have black eyes with a pupil which reflects red in bright light. It is also known as a "Colourpoint Black" and carries double recessives for "a" as well as "c(chm)" alleles.
Siamese - A Siamese gerbil starts out a light mushroom colour. Around eight weeks, it moults and the tail, nose, feet and tips of the ear go black. The main body colour stays the same. A Siamese has black eyes with a pupil which reflects red in bright light. It also often has a "bib" or white line running down the chin. It may also have some white on the paws.Younger Siamese gerbils can have lighter bands on their feet, but will fade on the back but may stay on the front. Their colour is also described as "Mushroom Colourpoint" or "Light Colourpoint Black" and they carry double recessives of the "a" allele, as well as one c(chm) and one c(h) allele.
Colourpoint Agouti - A Colourpoint Agouti gerbil has an off-white to grey base with a liberal amount of silvery-brownish ticking along the back. The tail is a ticked light gold and claws are black. The belly is white and the eyes are black with a pupil which reflects red in bright light. Also called simply "Colourpoint," sometimes abbreviated, "CPT." It carries double recessives of the "c(chm)" allele.
Light Colourpoint Agouti - A Light Colourpoint Agouti has an off-white base with silvery-brownish ticking along the back and dark claws. Its belly is white and its eyes are black with a pupil which reflects red in bright light. Also called "Light Colourpoint," sometimes abbreviated, "LCPT." It carries one "c(chm)" allele and one "c(h)" allele.
Grey Agouti - The hairs on the back of a Grey Agouti are dark grey with white in the middle, making an even salt-and-pepper look. They often have gold intermingled into the coat. The belly is white and claws are dark. A Grey Agouti has eyes which are black with a pupil which reflects red in bright light. It carries double recessives of the Underwhite dense gene, "uw(d)." This gene was formerly thought to be the Grey allele, "g."
Pearl - A Pearl gerbil, also called a "Colourpoint Grey Agouti" is a Colourpoint Agouti gerbil which carries double recessives for the "uw(d)" allele. It is a salt and pepper ticked grey gerbil with no gold colour on the tail and very even ticking all over. The ticking is less pronounced than on a Grey Agouti coat. It has black eyes with a pupil which reflects red in bright light and has grey or beige claws.
Slate - A Slate gerbil is a greyish black colour. Often has a "bib" or white line running down the chin. It may also have some white on the paws. It has grey claws. A Slate has black eyes with a pupil which reflects red in bright light. It carries double recessives of the "a" as well as the "uw(d)" alleles.
Ivory Cream - An Ivory Cream gerbil is cream or very pale yellow on its back with a lighter creamy white belly. It has ruby eyes. It is also called "White-bellied Cream" or "Ivory." It carries double recessives of the "p" as well as the "uw(d)" alleles.
Red-Eyed White - A Red-Eyed White gerbil is white all over. It has ruby eyes. Also known as Ruby Eyed White and abbreviated as "REW." It carries double recessives of the "a," "p" and "uw(d)" alleles.
Satin - a Satin gerbil is a light cream colour with a marked sheen and ruby eyes which darken with age. It has a white undercoat. It carries double recessives of the Underwhite gene, "uw."
Azure Slate - An Azure Slate gerbil is dark grey with black eyes. It carries double recessive genes for "a" as well as one Underwhite allele and one Underwhite Dense allele.
Dark Eyed Honey - A Dark Eyed Honey gerbil starts out with a bright orange back with a white belly and flanks. At eight weeks old it moults and a small amount of black ticking appears along its back. It carries double recessives of the "Extension of Yellow" gene, notated "e." A Dark Eyed Honey has black eyes. Dark Eyed Honey is often abbreviated as "DEH."
Nutmeg - A Nutmeg gerbil starts out with a bright orange colour over its entire body. At eight weeks old it moults and liberal black ticking appears along the back with a lesser amount on the belly, changing the colour from an orange to a rich ticked brown, depending on the extensiveness of the ticking. The normal moulting process may give this gerbil type a brindled appearance at times. A Nutmeg gerbil has black eyes. Nutmeg gerbils carry double recessives of the "a" and "e" alleles.
Silver Nutmeg - A Silver Nutmeg gerbil's first coat is an ivory or light peach colour. At eight weeks old the gerbil moults and the liberal greyish ticking appears along the back with a lesser amount on the belly. A Silver Nutmeg gerbil has black eyes with a pupil which reflects red in bright light and has dark claws. Silver Nutmegs carry double recessives of Underwhite Dense, "uw(d)" and Extension of Yellow, "e" as well as "a" alleles.
Red Eyed Honey - A Red Eyed Honey gerbil has a bright orange back with a white belly and flanks. It has ruby eyes. It is also known as a "Yellow Fox." Red Eyed Honey is often abbreviated as "REH." Red Eyed Honey gerbils carry double recessives of "e" and "p" alleles.
Saffron - A Saffron gerbil is a bright orange colour over its entire body, with the colour lightening somewhat through the belly area. Often there is a "bib" or white line running down the chin. There may also be some white on the paws. A Saffron gerbil has ruby eyes. It is also known as a "Red Fox." Saffron gerbils carry double recessives of "a" as well as "p" and "e" alleles.
Polar Fox - A Polar Fox starts out an ivory or light peach colour. At eight weeks old the gerbil moults and minimal greyish ticking appears along the back. The claws are brown. A Polar Fox has black eyes with a pupil which reflects red in bright light. A Polar Fox gerbil carries double recessives of the "e" and "uw(d)" alleles.
Schimmel - A Schimmel gerbil starts out as an orange colour. At eight weeks old it moults and the back begins to lighten to a creamy white. The gerbil's body continues to lighten throughout its life until it can be left with a creamy white body, while the tail, nose, feet and tips of the ears retain the orange. Schimmel gerbils have black eyes. A Schimmel gerbil carries double recessives of the Schimmel gene, notated as "e(f)." A Schimmel with ruby eyes due to carrying double "p" recessive alleles is a Red Eyed Schimmel, also called a Ruby Eyed Schimmel.
Blue - A Blue gerbil is a dark grey colour, sometimes with very faint ticking. Its pigment is slightly lighter on the tail, ears and paws. It has black eyes. It carries double recessives of the Dilute gene, abbreviated, "d."
Smoke - A Smoke coloured gerbil is a medium to dark grey colour with dark eyes. It carries double recessives for both "d" and "uw(d)" alleles.
Black Eyed White - A Black Eyed White gerbil is completely white with black eyes. Some have greyish ear tips and dark claws. Black Eyed White gerbils are often the result of combining many different recessive genes--for example, a Light Colourpoint Dark Eyed Honey, "LCP DEH" which carries double recessives of the "e" alleles as well as a "c(h)" and a "c(chm)" allele, but always retaining a dominant gene for Pink Eyed, "P." The only exceptions would be if double recessives of the Himalayan gene or the Underwhite gene are present, which will turn a Pink Eyed dominant gerbil's eyes to ruby.
Spotting - Dominant spotting can be in any coat variety and will lighten the fur around it. How the spotting will look depends on modifiers. The claws of a spotted gerbil are a pale colour. Spotting types that don't conform to show standards are usually classed as patched. Spotting is notated as "Sp."
Collared - A thick, unbroken band of spotting around the neck connecting to the white belly.
Collar and blaze - A thick, unbroken band of spotting around the neck connecting to the white belly and an unbroken white blaze connecting the three spotting areas (neck, forehead and nose).
Pied - The base coat colour may be of any standard type except for white. There is a thick band of white around the neck and shoulder area to form a collar that is connected to a blazed down the forehead and face. The distinguishing feature are small spots on the rump and back area around the spinal area. These spots usually do not have clear edges. The gerbil may be 50% white before it is considered a mottled gerbil as long as the spotting pattern conforms to the standard, accepted pattern.
Mottled - The coat colour of the gerbil may be any standard coat colour broken by small white patches accompanying a collar and blaze. The gerbil may be up to 75% white until it would be considered a variegated gerbil.
Variegated - The variegated pattern is when any standard coat colour is broken up by small white patches along with a collar and blaze. The difference between the variegated spotting form and the mottled spotting form is the amount of white. The variegated spotting is an extended form of mottling. There is more white on the back and rump, allowing less colour to show through. This can form a "dalmatian" pattern. Often the tail tuft and the end of the tail is white or lacking pigment.
Extreme White - The extreme white pattern is associated with any standard colour except for white. Here the coat colour is 90% white and barely any of the base coat colour, or any pigment, is remaining. There have been health concerns circulating about extreme white gerbils. Head tilts, lack of good balance, and repetitive running and circling has been reported in these gerbils. It has been found that these health concerns mostly affect gerbils with unpigmented (light pink/not very opaque) ears.
Dark Patched Pied/Spotted - When a somatic reversion mutation causes a dark spot of the original, unlightened fur to appear on a spotted gerbil, it is called Dark Patched Pied. This trait does not conform to standard Mendelian inheritance patterns though certain lineages are more prone to produce it.
Note: some coat varieties, for example Yellow Fox, are described as fox strains despite not carrying the fox gene
Mongolian Gerbil Young
These rodents are widely used as subjects of testing within laboratoriesfor a plethora of different reasons. These rodents are susceptible to carrying diseases and infections some transmitted sexually, much the subject of many experiments within labs. In the wild, Wild Mongolian gerbils breed during the months of February and October. Males do not become sexually mature for about 70-80 days, while the vaginal opening occurs in females about 33-50 days after birth. For other gerbils such as the hairy footed gerbil, sexual maturity has a slightly earlier and longer window of 60-90 days in comparison with a later and shorter window for Mongolian gerbils, 70-84 days . Females reach sexual maturity shortly after this opening occurs. Mongolian gerbils are regarded as monogamous within science. Even with this said, many Mongolian Gerbils have still been found in laboratory tests regarding their sexual reproduction behavior to have shown signs of "cheating" when not in contact with their initial mate in laboratory setting.  Cheating meaning showing signs of promiscuity and mating with other females while their monogamous partner is absent. Gerbils are for the most part selective when it comes to picking a mate for copulation; though their selection process occurs more rapid than other species due to the high amount of gerbil population and shorter life span. An average litter size for the Mongilian Gerbil would be around 1-2 pups, if the litter only contains around 1-2 young than the mother will neglect them and they will die from starvation.Mongolian Gerbils are monogamous and mate with their selected partner for the rest of their time together, when one becomes widowed many girbils refrain from seeking other mates to reproduce with. Obviously not every single gerbil is going to act the same after losing their mate but for the most part these rodents do not seek additional partners after the fact. When older females lose their mate they almost all of the time give up on seeking reproduction. Their behavior tends to vary when faced with different settings, within the wild finding and selecting a mate is not a problem at all due to the high frequency of mates. Within a laboratory setting many gerbils tend to keep to themselves and refrain from copulation. 
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