How many chromosomes do different animals have? How many chromosomes does a cat have? Genetics provides data on various genomes Number of chromosomes in animals
- In total, 7 genera of hamsters are known, including about 19 species. The largest is the common hamster (up to 35 cm in length, weight up to 400 g or more), the smallest is the Roborovsky hamster (4–5 cm in length, weight usually does not exceed 10 g).
- In the wild, hamsters can be found in the steppes, semi-deserts and deserts of Eurasia. Some hamsters climb mountains up to 4000 m, some happily live next to humans - in fields, gardens, orchards, and even in buildings.
- A popular pet in many countries, the golden or Syrian hamster has a rather limited range in nature - it can be found in western Syria and the border regions of Turkey. Millions of animals of this species, living in homes and laboratories around the world, all descend from a single litter obtained by Professor Aharoni in 1930. The hamsters were successfully reproduced, and a year later, part of the resulting offspring was exported to England, from where they began their further “march around the world” as domestic and laboratory animals.
- Several other species are also kept in captivity: the Chinese hamster, and representatives of the genus of hairy hamsters - the Djungarian, Campbell's hamster and Roborovsky's hamster. The rest are practically unknown to anyone except zoological specialists.
- The idea of hamsters as good-natured bumpkins is not entirely true. Most of them are quite aggressive animals. In nature, almost all hamsters lead a solitary lifestyle, without maintaining any constant positive contacts with their fellow tribesmen. The male, by smell, finds a female ready for mating, mates with her, and this is where his participation in procreation usually ends - the female raises the cubs alone. This asociality of hamsters also extends to communication with humans: in captivity, they are, as a rule, poorly tamed, do not become attached to the owner and are not interested in communicating with him. In lines that have been raised in captivity for many generations, aggression towards humans is usually stopped, but one should not expect the same from animals caught in the wild: when you try to pick them up, they will bite furiously, and in representatives of relatively large species the bites can be very painful.
- Contrary to popular belief, hamster burrows are almost never complex. In general, the life of a single person is not conducive to acquiring a large and complex home. A hamster's burrow usually has one or two exits, a nesting chamber and, in some cases, a storage room. But the volume of reserves in some species can be very significant. Hamsters do not fall into a real long-term hibernation (like gophers, for example), so they have to take care of a “food warehouse” for the winter - so that it would not be so sad to while away the long winter evenings.
- One of the most famous features of hamsters is their cheek pouches. This device really deserves at least a special mention. It is clear that in order to create any significant feed reserves, you need to have a device for their transportation. In this case, evolution “tried” - in the cheek pouches, hamsters can carry a volume of food comparable to the size of the hamster itself.
- As everyone knows, the basis of a hamster’s diet is grain (seeds of various plants, both wild and cultivated). However, in addition to this, hamsters can use a variety of food sources. The green parts of plants are used mainly as a source of water - since abundant dew does not always fall, and hamsters most often have no other ways to get water in nature. Some species of hamsters can happily eat various fruits and roots. Also, most species, to one degree or another, exhibit predatory tendencies and make up for the lack of protein through animal food - from insects to frogs and lizards.
- The uniformity of the “hamster” appearance and lifestyle has its exceptions. For example, the name of the rat-shaped hamster speaks for itself - in appearance it can really be confused with a rat. The “rat” color, the elongated body shape, the relatively long tail - all this goes well with the “rat” lifestyle: unlike other species of hamsters, the rat hamster inhabits relatively moist habitats and has an appropriate metabolism.
- In total, 7 genera of hamsters are known, including about 19 species. About - because the status of some forms remains a subject of debate among zoologists. Djungarian and Campbell's hamsters were previously considered one species, but now the species status of each of them is beyond doubt. But some researchers consider the Barabinsk, Transbaikal and Chinese hamsters to be different species, while others consider them to be forms within one polymorphic species. They differ in the number of chromosomes, but produce fertile offspring.
Djungarian hamster (Phodopus sungarus; English Jungariae hamster). Distributed in the steppe and semi-steppe parts of Western and Eastern Siberia, northeast Kazakhstan, Mongolia.
Djungarian hamsters have been used as experimental and laboratory animals since the 60s of the 20th century. These are very docile and peaceful animals, gray in color with a black stripe along the back. The maximum size of adult individuals is 100 mm, and their weight is 30-40 g (Fig. 97.4).
The length of all the intestines of the Djungarian hamster is 37.5-52.6 cm, the cecum is 3.1-5.4 cm; spleen - 1.5-2.0 cm, testicles - 1.5-1.6 cm. Heart weight - 160-330 mg, kidney - 180-320 mg, liver - 1200-3300 mg. Relative mass of the main internal organs (index): heart - 5.1%, kidneys - 5.9%, liver - 52.3%. Sexual maturity in females occurs on the 30-60th day, in males on the 45-60th day of life. The estrous cycle lasts 4-5 days and is regular. The estrus stage takes 12 hours and is easily determined by examining vaginal smears. They reproduce well in captivity.
The duration of pregnancy of a female Djungarian hamster is 16-18 days, i.e. very short. The lactation period averages 20 days. The average number of litters is 5, but can be up to 12 or even 18 (O.I. Sokova et al., 1973). The number of cubs is from 1 to 9 (on average 5-6). The weight of a newborn is 1.5-2.2 g. They begin to see clearly on days 9-11. By the 15th day, the cubs switch to the adult diet. The animals become sexually mature by the age of two months, and begin to reproduce from the age of four months.
Djungarian hamsters are active at dusk and at night. They feed on seeds, green parts of plants and insects. Seed reserves are prepared for the winter. They do not hibernate. The diet of Djungarian hamsters is no different from the diet of golden hamsters.
The lifespan of Djungarian hamsters is up to 3 years. They tolerate captivity well, in cages intended for mice. It should be borne in mind that Djungarian hamsters must be kept in dry, well-ventilated rooms in which air humidity should not exceed 40-50%. In Djungarian hamsters under the age of 8 months, spontaneous tumors were observed in 10% of cases, and in older age groups they were observed in 30% of cases. Spontaneous tumors in the vast majority of cases affected the areas of the nose, skin, lips, jaws, mammary glands, and lungs. In the later stages of ontogenesis, tumors of the mammary glands, ovaries, and uterus became more frequent, and skin tumors occurred less frequently. Most of the neoplasms in Djungarian hamsters were cancerous tumors. The most common benign tumors were liver adenomas and skin papillomas. These animals are sensitive to the carcinogenic effects of dimethylbenzanthracene, methylcholanthrene and resistant to the carcinogenic effects of urethane.
Djungarian hamsters are resistant to paratyphoid pathogens, ectromelia, and trichophytosis. Animals are characterized by a small number of chromosomes - their karyotype consists of 14 pairs, which makes it possible to use these new laboratory animals for cytogenetic studies of chromosomes,
Djungarian hamsters tolerate inbreeding worse than mice, which makes it difficult to breed linear animals.
What mutations, besides Down syndrome, threaten us? Is it possible to cross a man with a monkey? And what will happen to our genome in the future? The editor of the portal ANTHROPOGENES.RU talked about chromosomes with a geneticist, head. lab. comparative genomics SB RAS Vladimir Trifonov.
− Can you explain in simple language what a chromosome is?
− A chromosome is a fragment of the genome of any organism (DNA) in complex with proteins. If in bacteria the entire genome is usually one chromosome, then in complex organisms with a pronounced nucleus (eukaryotes) the genome is usually fragmented, and complexes of long fragments of DNA and protein are clearly visible in a light microscope during cell division. That is why chromosomes as colorable structures (“chroma” - color in Greek) were described at the end of the 19th century.
− Is there any relationship between the number of chromosomes and the complexity of an organism?
- There is no connection. The Siberian sturgeon has 240 chromosomes, the sterlet has 120, but it is sometimes quite difficult to distinguish these two species from each other based on external characteristics. Female Indian muntjac have 6 chromosomes, males have 7, and their relative, the Siberian roe deer, has more than 70 (or rather, 70 chromosomes of the main set and up to a dozen additional chromosomes). In mammals, the evolution of chromosome breaks and fusions proceeded quite intensively, and now we are seeing the results of this process, when each species often has characteristic features of its karyotype (set of chromosomes). But, undoubtedly, the general increase in genome size was a necessary step in the evolution of eukaryotes. At the same time, how this genome is distributed into individual fragments does not seem to be very important.
− What are some common misconceptions about chromosomes? People often get confused: genes, chromosomes, DNA...
− Since chromosomal rearrangements do occur frequently, people have concerns about chromosomal abnormalities. It is known that an extra copy of the smallest human chromosome (chromosome 21) leads to a rather serious syndrome (Down syndrome), which has characteristic external and behavioral features. Extra or missing sex chromosomes are also quite common and can have serious consequences. However, geneticists have also described quite a few relatively neutral mutations associated with the appearance of microchromosomes, or additional X and Y chromosomes. I think the stigmatization of this phenomenon is due to the fact that people perceive the concept of normal too narrowly.
− What chromosomal mutations occur in modern humans and what do they lead to?
− The most common chromosomal abnormalities are:
− Klinefelter syndrome (XXY men) (1 in 500) – characteristic external signs, certain health problems (anemia, osteoporosis, muscle weakness and sexual dysfunction), sterility. There may be behavioral features. However, many symptoms (except sterility) can be corrected by administering testosterone. Using modern reproductive technologies, it is possible to obtain healthy children from carriers of this syndrome;
− Down syndrome (1 in 1000) – characteristic external signs, delayed cognitive development, short life expectancy, may be fertile;
− trisomy X (XXX women) (1 in 1000) – most often there are no manifestations, fertility;
− XYY syndrome (men) (1 in 1000) – almost no manifestations, but there may be behavioral characteristics and possible reproductive problems;
− Turner syndrome (women with CP) (1 in 1500) – short stature and other developmental features, normal intelligence, sterility;
− balanced translocations (1 in 1000) – depends on the type, in some cases developmental defects and mental retardation may be observed and may affect fertility;
− small additional chromosomes (1 in 2000) – the manifestation depends on the genetic material on the chromosomes and varies from neutral to serious clinical symptoms;
Pericentric inversion of chromosome 9 occurs in 1% of the human population, but this rearrangement is considered a normal variant.
Is the difference in the number of chromosomes an obstacle to crossing?
− If the crossing is intraspecific or between closely related species, then the difference in the number of chromosomes may not interfere with crossing, but the descendants may turn out to be sterile. There are a lot of hybrids known between species with different numbers of chromosomes, for example, equines: there are all kinds of hybrids between horses, zebras and donkeys, and the number of chromosomes in all equines is different and, accordingly, the hybrids are often sterile. However, this does not exclude the possibility that balanced gametes may be produced by chance.
- What unusual things have been discovered recently in the field of chromosomes?
− Recently, there have been many discoveries regarding the structure, function and evolution of chromosomes. I especially like the work that showed that sex chromosomes were formed completely independently in different groups of animals.
- Still, is it possible to cross a man with a monkey?
- Theoretically, it is possible to obtain such a hybrid. Recently, hybrids of much more evolutionarily distant mammals (white and black rhinoceros, alpaca and camel, and so on) have been obtained. The red wolf in America has long been considered a separate species, but has recently been proven to be a hybrid between a wolf and a coyote. There are a huge number of feline hybrids known.
- And a completely absurd question: is it possible to cross a hamster with a duck?
- Here, most likely, nothing will work out, because too many genetic differences have accumulated over hundreds of millions of years of evolution for the carrier of such a mixed genome to function.
- Is it possible that in the future a person will have fewer or more chromosomes?
- Yes, this is quite possible. It is possible that a pair of acrocentric chromosomes will merge and such a mutation will spread throughout the population.
− What popular science literature do you recommend on the topic of human genetics? What about popular science films?
− Books by biologist Alexander Markov, the three-volume “Human Genetics” by Vogel and Motulsky (though this is not science-pop, but there is good reference data there). Nothing comes to mind from films about human genetics... But Shubin’s “Inner Fish” is an excellent film and book of the same name about the evolution of vertebrates.
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