How many chromosomes does a caterpillar have? Chromosomes
The term chromosome was first proposed by V. It is very difficult to identify chromosome bodies in the nuclei of interphase cells using morphological methods. The chromosomes themselves, as clear, dense bodies clearly visible in a light microscope, are revealed only shortly before cell division.
Share your work on social networks
If this work does not suit you, at the bottom of the page there is a list of similar works. You can also use the search button
Lecture No. 6
CHROMOSOMES
Chromosomes are the main functional autoreproducing structure of the nucleus, in which DNA is concentrated and with which the functions of the nucleus are associated. The term “chromosomes” was first proposed by W. Waldeyer in 1888.
It is very difficult to identify chromosome bodies in the nuclei of interphase cells using morphological methods. The chromosomes themselves, as clear, dense bodies that are clearly visible in a light microscope, are revealed only shortly before cell division. In the interphase itself, chromosomes as dense bodies are not visible, since they are in a loosened, decondensed state.
Number and morphology of chromosomes
The number of chromosomes is constant for all cells of a given species of animal or plant, but varies significantly among different objects. It is not related to the level of organization of living organisms. Primitive organisms can have many chromosomes, while highly organized ones have much fewer. For example, in some radiolarians the number of chromosomes reaches 1000-1600. The record holder among plants for the number of chromosomes (about 500) is the grass fern; the mulberry tree has 308 chromosomes. Let us give examples of the quantitative content of chromosomes in some organisms: crayfish 196, humans 46, chimpanzees 48, soft wheat 42, potatoes 18, fruit flies 8, house flies 12. The smallest number of chromosomes (2) is observed in one of Ascaris races, the Asteraceae plant Haplopapus has only 4 chromosomes.
The size of chromosomes varies widely among different organisms. Thus, the length of chromosomes can vary from 0.2 to 50 microns. The smallest chromosomes are found in some protozoa, fungi, and algae; very small chromosomes are found in flax and sea reeds; they are so small that they are difficult to see with a light microscope. The longest chromosomes are found in some orthopteran insects, amphibians and liliaceae. The length of human chromosomes is in the range of 1.5-10 microns. The thickness of chromosomes ranges from 0.2 to 2 microns.
The morphology of chromosomes is best studied at the moment of their greatest condensation, in metaphase and at the beginning of anaphase. The chromosomes of animals and plants in this state are rod-shaped structures of different lengths with a fairly constant thickness; in most chromosomes it is easy to find the zoneprimary constriction, which divides the chromosome into two shoulder . In the area of the primary constriction there is centromere or kinetochore . It is a plate-like, disc-shaped structure. It is connected by thin fibrils to the body of the chromosome in the region of the constriction. The kinetochore is poorly understood structurally and functionally; Thus, it is known that it is one of the centers of tubulin polymerization; bundles of microtubules of the mitotic spindle grow from it, going towards the centrioles. These bundles of microtubules take part in the movement of chromosomes to the poles of the cell during mitosis. Some chromosomes havesecondary constriction. The latter is usually located near the distal end of the chromosome and separates a small section satellite . The size and shape of the satellite are constant for each chromosome. The size and length of the secondary constrictions are also very constant. Some secondary constrictions are specialized regions of chromosomes associated with the formation of the nucleolus (nucleolar organizers); others are not associated with the formation of the nucleolus and their functional role is not fully understood. Chromosome arms end in terminal sections telomeres. The telomeric ends of chromosomes are not able to join with other chromosomes or their fragments, in contrast to the ends of chromosomes lacking telomeric regions (as a result of breaks), which can join the same broken ends of other chromosomes.
Based on the location of the primary constriction (centromere), the following are distinguished: types of chromosomes:
1. metacentricthe centromere is located in the middle, the arms are equal or almost equal in length, in metaphase it acquires V-shape;
2. submetacentricthe primary constriction is slightly shifted to one of the poles, one arm is slightly longer than the other, in metaphase it has L-shape;
3. acrocentricthe centromere is strongly shifted to one of the poles, one arm is much longer than the other, does not bend in metaphase and has a rod-shaped shape;
4. telocentricThe centromere is located at the end of the chromosome, but such chromosomes have not been found in nature.
Usually each chromosome has only one centromere (monocentric chromosomes), but chromosomes can occur dicentric (with 2 centromeres) andpolycentric(possessing many centromeres).
There are species (for example, sedges) in which the chromosomes do not contain visible centromeric regions (chromosomes with diffusely located centromeres). They're called acentric and are not able to perform ordered movement during cell division.
Chemical composition of chromosomes
The main components of chromosomes are DNA and basic proteins (histones). DNA complex with histonesdeoxyribonucleoprotein(DNP) constitutes about 90% of the mass of both chromosomes isolated from interphase nuclei and chromosomes of dividing cells. The DNP content is constant for each chromosome of a given species of organism.
Of the mineral components, the most important are calcium and magnesium ions, which give plasticity to chromosomes, and their removal makes the chromosomes very fragile.
Ultrastructure
Each mitotic chromosome is covered on top pellicle . Inside is matrix , in which a spirally twisted DNP thread with a thickness of 4-10 nm is located.
Elementary fibrils of DNP are the main component that is included in the structure of mitotic and meiotic chromosomes. Therefore, to understand the structure of such chromosomes, it is necessary to know how these units are organized as part of the compact chromosome body. Intensive study of chromosome ultrastructure began in the mid-50s of the last century, which is associated with the introduction of electron microscopy into cytology. There are 2 hypotheses for the organization of chromosomes.
1). Unimute the hypothesis states that there is only one double-stranded DNP molecule on the chromosome. This hypothesis has morphological, autoradiographic, biochemical and genetic confirmation, which makes this point of view the most popular today, since at least for a number of objects (drosophila, yeast) it is proven.
2). Polynemic the hypothesis is that several double-stranded DNP molecules are combined into a bundle chromonema , and, in turn, 2-4 chromonemas, twisting, form a chromosome. Almost all observations of chromosome polynemism were made using a light microscope on botanical objects with large chromosomes (lilies, various onions, beans, tradescantia, peony). It is possible that the phenomena of polynemia that were observed in the cells of higher plants are characteristic only of these objects.
Thus, it is possible that there are several different principles for the structural organization of chromosomes in eukaryotic organisms.
In interphase cells, many regions of chromosomes are despiralized, which is associated with their functioning. They're called euchromatin. It is believed that the euchromatic regions of the chromosomes are active and contain the entire main set of genes of the cell or organism. Euchromatin is observed in the form of fine granularity or is not visible at all in the nucleus of an interphase cell.
During the cell transition from mitosis to interphase, certain zones of different chromosomes or even entire chromosomes remain compact, spiralized and well stained. These zones are called heterochromatin . It is present in the cell in the form of coarse grains, lumps, and flakes. Heterochromatic regions are usually located in the telomeric, centromeric, and perinucleolar regions of chromosomes, but can also be part of their internal parts. The loss of even significant sections of heterochromatic regions of chromosomes does not lead to cell death, since they are not active and their genes temporarily or permanently do not function.
Matrix is a component of mitotic chromosomes of plants and animals, released during despiralization of chromosomes and consisting of fibrillar and granular structures of ribonucleoprotein nature. Perhaps the role of the matrix is the transfer of RNA-containing material by chromosomes, which is necessary both for the formation of nucleoli and for the restoration of the karyoplasm itself in daughter cells.
Chromosome set. Karyotype
The constancy of such characteristics as size, location of primary and secondary constrictions, the presence and shape of satellites determines the morphological individuality of chromosomes. Thanks to this morphological individuality, in many species of animals and plants it is possible to recognize any chromosome set in any dividing cell.
The totality of the number, size and morphology of chromosomes is called karyotype of this type. A karyotype is like the face of a species. Even in closely related species, chromosome sets differ from each other either in the number of chromosomes, or in the size of at least one or several chromosomes, or in the shape of the chromosomes and their structure. Consequently, the structure of the karyotype can be a taxonomic (systematic) character, which is increasingly used in the taxonomy of animals and plants.
A graphic representation of a karyotype is called idiogram.
The number of chromosomes in mature germ cells is called haploid (denoted n ). Somatic cells contain double the number of chromosomes diploid set (2 n ). Cells that have more than two sets of chromosomes are called polyploid (3 n, 4 n, 8 n, etc.).
The diploid set contains paired chromosomes that are identical in shape, structure and size, but have different origins (one is maternal, the other is paternal). They're called homologous.
In many higher dioecious animals in the diploid set there are one or two unpaired chromosomes that differ in males and females, this sexual chromosomes. The remaining chromosomes are called autosomes . Cases have been described when a male has only one sex chromosome, and a female has two.
In many fish, mammals (including humans), some amphibians (frogs of the genus Rana ), insects (beetles, Diptera, Orthoptera), the large chromosome is designated by the letter X, and the small by the letter Y. In these animals, in the karyotype of the female, the last pair is represented by two XX chromosomes, and in the male, by XY chromosomes.
In birds, reptiles, certain species of fish, some amphibians (tailed amphibians), and butterflies, the male sex has the same sex chromosomes ( WW -chromosomes), and the female are different ( WZ chromosomes).
In many animals and humans, in the cells of female individuals, one of the two sex chromosomes does not function and therefore remains entirely in a spiraled state (heterochromatin). It is found in the interphase nucleus in the form of a lumpsex chromatinat the inner nuclear membrane. Both sex chromosomes function throughout life in the male body. If sex chromatin is detected in the nuclei of the cells of a male body, this means that he has an extra X chromosome (XXY Kleinfelter's disease). This may occur as a result of impaired spermato- or oogenesis. The study of the content of sex chromatin in interphase nuclei is widely used in medicine to diagnose human chromosomal diseases caused by an imbalance of sex chromosomes.
Karyotype changes
Changes in the karyotype may be associated with a change in the number of chromosomes or a change in their structure.
Quantitative changes in karyotype: 1) polyploidy; 2) aneuploidy.
Polyploidy this is a multiple increase in the number of chromosomes compared to haploid. As a result, instead of ordinary diploid cells (2 n ) are formed, for example, triploid (3 n ), tetraploid (4 n ), octaploid (8 n ) cells. Thus, in onions, whose diploid cells contain 16 chromosomes, triploid cells contain 24 chromosomes, and tetraploid cells contain 32 chromosomes. Polyploid cells are large in size and have increased viability.
Polyploidy is widespread in nature, especially among plants, many species of which arose as a result of multiple doublings of the number of chromosomes. Most cultivated plants, for example, bread wheat, multi-row barley, potatoes, cotton, and most fruit and ornamental plants, are naturally occurring polyploids.
Experimentally, polyploid cells are most easily obtained by the action of an alkaloid colchicine or other substances that disrupt mitosis. Colchicine destroys the spindle, so that already doubled chromosomes remain in the equatorial plane and do not diverge to the poles. After the cessation of the action of colchicine, the chromosomes form a common nucleus, but a larger one (polyploid). During subsequent divisions, the chromosomes will again double and move towards the poles, but twice the number of them will remain. Artificially obtained polyploids are widely used in plant breeding. Varieties of triploid sugar beet, tetraploid rye, buckwheat and other crops have been created.
In animals, complete polyploidy is very rare. For example, in the mountains of Tibet there lives one of the species of frogs, the population of which on the plain has a diploid chromosome set, and the high-mountain populations have a triploid, or even tetraploid.
In humans, polyploidy leads to sharply negative consequences. The birth of children with polyploidy is extremely rare. Usually the death of the organism occurs at the embryonic stage of development (about 22.6% of all spontaneous abortions are caused by polyploidy). It should be noted that triploidy occurs 3 times more often than tetraploidy. If children with triploidy syndrome are nevertheless born, they have abnormalities in the development of external and internal organs, are practically non-viable and die in the first days after birth.
Somatic polyploidy is more often observed. Thus, in human liver cells, with age, dividing cells become less and less, but the number of cells with a large nucleus or two nuclei increases. Determining the amount of DNA in such cells clearly shows that they have become polyploid.
Aneuploidy this is an increase or decrease in the number of chromosomes that is not a multiple of the haploid number. Aneuploid organisms, that is, organisms in which all cells contain aneuploid sets of chromosomes, are usually sterile or poorly viable. As an example of aneuploidy, consider some human chromosomal diseases. Kleinfelter's syndrome: the cells of the male body have an extra X chromosome, which leads to general physical underdevelopment of the body, in particular its reproductive system, and mental abnormalities. Down syndrome: an extra chromosome is contained in the 21st pair, which leads to mental retardation, abnormalities of internal organs; the disease is accompanied by some external signs of dementia and occurs in men and women. Turner syndrome is caused by the lack of one X chromosome in the cells of the female body; manifests itself in underdevelopment of the reproductive system, infertility, and external signs of dementia. If one X chromosome is missing in the cells of the male body, death occurs at the embryonic stage.
Aneuploid cells constantly arise in a multicellular organism as a result of disruption of the normal course of cell division. As a rule, such cells quickly die, but in some pathological conditions of the body they reproduce successfully. A high percentage of aneuploid cells is characteristic, for example, of many malignant tumors of humans and animals.
Structural changes in the karyotype.Chromosomal rearrangements, or chromosomal aberrations, occur as a result of single or multiple breaks of chromosomes or chromatids. Chromosome fragments at break sites are able to connect with each other or with fragments of other chromosomes in the set. Chromosomal aberrations are of the following types. Deletion this is the loss of the middle section of the chromosome. Difference this is the detachment of the end section of a chromosome. Inversion tearing off a section of a chromosome, rotating it 180 0 and joining to the same chromosome; this disrupts the order of nucleotides. Duplication breaking off a section of a chromosome and attaching it to a homologous chromosome. Translocation detachment of a section of a chromosome and its attachment to a non-homologous chromosome.
As a result of such rearrangements, dicentric and acentric chromosomes can be formed. Large deletions, differentiations and translocations dramatically change the morphology of chromosomes and are clearly visible under a microscope. Small deletions and translocations, as well as inversions, are detected by changes in the inheritance of genes localized in regions of chromosomes affected by the rearrangement, and by changes in the behavior of chromosomes during the formation of gametes.
Structural changes in the karyotype always lead to negative consequences. For example, “cry of the cat” syndrome is caused by a chromosomal mutation (division) in the 5th pair of chromosomes in humans; manifests itself in abnormal development of the larynx, which leads to “meowing” instead of a normal cry in early childhood, and retardation in physical and mental development.
Chromosome reduplication
The basis of the doubling (reduplication) of chromosomes is the process of DNA replication, i.e. the process of self-reproduction of nucleic acid macromolecules, ensuring accurate copying of genetic information and its transmission from generation to generation. DNA synthesis begins with the divergence of strands, each of which serves as a template for the synthesis of a daughter strand. The products of reduplication are two daughter DNA molecules, each of which consists of one parent and one daughter strand. An important place among reduplication enzymes is occupied by DNA polymerase, which carries out synthesis at a rate of about 1000 nucleotides per second (in bacteria). DNA reduplication is semi-conservative, i.e. during the synthesis of two daughter DNA molecules, each of them contains one “old” and one “new” chain (this method of reduplication was proven by Watson and Crick in 1953). Fragments synthesized during reduplication on one strand are “crosslinked” by the enzyme DNA ligase.
Reduplication involves proteins that unwind the DNA double helix, stabilize the untwisted sections, and prevent the molecules from becoming entangled.
DNA reduplication in eukaryotes occurs more slowly (about 100 nucleotides per second), but simultaneously at many points in one DNA molecule.
Since protein synthesis also occurs simultaneously with DNA reduplication, we can talk about chromosome reduplication. Studies conducted back in the 50s of the twentieth century showed that no matter how many longitudinally arranged DNA strands the chromosomes of organisms of different species contain, during cell division the chromosomes behave as if they consist of two simultaneously reduplicating subunits. After reduplication, which occurs in interphase, each chromosome turns out to be double, and even before division begins in the cell, everything is ready for an even distribution of chromosomes between daughter cells. If division does not occur after reduplication, the cell becomes polyploid. During the formation of polytene chromosomes, chromonemas are reduplicated, but do not diverge, due to which giant chromosomes with a huge number of chromonemas are obtained.
Other similar works that may interest you.vshm> |
|||
| 8825. | Mitotic subclinus. Budova chromosomes | 380.96 KB | |
| Budov's chromosomes Laboratory work No. 5 Meta: systematize and distil students' knowledge about the life cycle of the child; about mitosis of its biological significance; It is wise to formulate and use a light microscope in the early phases of mitosis to install them with microphotographs... | |||
| 16379. | At the same time, the challenges without overcoming which our country cannot become one of the modern ones have become even more clearly defined. | 14.53 KB | |
| At the same time, being inherent in their nature to the historical roots of Russia, they aggravate the effect of the crisis on the general situation in Russia and especially on the possibility of overcoming crisis phenomena. Since the middle class, which stabilized the situation in society, was lost in its previous form in Russia for a long time, current fluctuations in the purchasing power of the majority of the population depend on the presence of a stable job and other generally low incomes in the form of side earnings and social benefits. those who have official status in Russia... | |||
| 20033. | Plasmodium malaria. Morphology. Development cycles. Immunity against malaria. Chemotherapy drugs | 2.35 MB | |
| Malarial plasmodium undergoes a complex life cycle of development, which occurs in the human body (asexual cycle, or schizogony) and mosquito (sexual cycle, or sporogony). The development of the causative agent of malaria in the human body - schizogony - is represented by two cycles: the first of them occurs in liver cells (tissue, or extra-erythrocytic, schizogony), and the second - in red blood cells (erythrocyte schizogony). | |||
| 6233. | Structure and functions of the nucleus. Morphology and chemical composition of the nucleus | 10.22 KB | |
| The nuclei are usually separated from the cytoplasm by a clear boundary. Bacteria and blue-green algae do not have a formed nucleus: their nucleus lacks a nucleolus and is not separated from the cytoplasm by a clearly defined nuclear membrane and is called a nucleoid. Core shape. | |||
Poor ecology, life in constant stress, priority of career over family - all this has a bad effect on a person’s ability to bear healthy offspring. Sadly, about 1% of babies born with serious chromosome abnormalities grow up mentally or physically retarded. In 30% of newborns, deviations in the karyotype lead to the formation of congenital defects. Our article is devoted to the main issues of this topic.
The main carrier of hereditary information
As is known, a chromosome is a certain nucleoprotein (consisting of a stable complex of proteins and nucleic acids) structure inside the nucleus of a eukaryotic cell (that is, those living beings whose cells have a nucleus). Its main function is the storage, transmission and implementation of genetic information. It is visible under a microscope only during processes such as meiosis (division of a double (diploid) set of chromosome genes during the creation of germ cells) and mycosis (cell division during the development of the organism).
As already mentioned, a chromosome consists of deoxyribonucleic acid (DNA) and proteins (about 63% of its mass) on which its thread is wound. Numerous studies in the field of cytogenetics (the science of chromosomes) have proven that DNA is the main carrier of heredity. It contains information that is subsequently implemented in a new organism. This is a complex of genes responsible for hair and eye color, height, number of fingers, etc. Which genes will be passed on to the child are determined at the time of conception.
Formation of the chromosome set of a healthy organism
A normal person has 23 pairs of chromosomes, each of which is responsible for a specific gene. There are 46 in total (23x2) - how many chromosomes a healthy person has. We get one chromosome from our father, the other is passed on from our mother. The exception is 23 pairs. It is responsible for the gender of a person: female is designated as XX, and male as XY. When the chromosomes are in a pair, this is a diploid set. In germ cells they are separated (haploid set) before being subsequently united during fertilization.
The set of characteristics of chromosomes (both quantitative and qualitative) examined within one cell is called a karyotype by scientists. Violations in it, depending on the nature and severity, lead to the occurrence of various diseases.
Deviations in the karyotype
When classified, all karyotype abnormalities are traditionally divided into two classes: genomic and chromosomal.
With genomic mutations, an increase in the number of the entire set of chromosomes, or the number of chromosomes in one of the pairs, is noted. The first case is called polyploidy, the second - aneuploidy.
Chromosomal abnormalities are rearrangements both within and between chromosomes. Without going into scientific jungle, they can be described as follows: some sections of chromosomes may not be present or may be doubled to the detriment of others; The sequence of genes may be disrupted, or their location may be changed. Disturbances in structure can occur in every human chromosome. Currently, the changes in each of them are described in detail.
Let us take a closer look at the most well-known and widespread genomic diseases.
Down syndrome
It was described back in 1866. For every 700 newborns, as a rule, there is one baby with a similar disease. The essence of the deviation is that a third chromosome is added to the 21st pair. This happens when the reproductive cell of one of the parents has 24 chromosomes (with double 21). The sick child ends up with 47 chromosomes – that’s how many chromosomes a Down person has. This pathology is facilitated by viral infections or ionizing radiation suffered by parents, as well as diabetes.
Children with Down syndrome are mentally retarded. Manifestations of the disease are visible even in appearance: an overly large tongue, large, irregularly shaped ears, a skin fold on the eyelid and a wide bridge of the nose, whitish spots in the eyes. Such people live on average forty years, because, among other things, they are susceptible to heart disease, problems with the intestines and stomach, and undeveloped genitals (although women may be capable of childbearing).
The older the parents, the higher the risk of having a sick child. Currently, there are technologies that make it possible to recognize a chromosomal disorder at an early stage of pregnancy. Older couples need to undergo a similar test. It will not hurt young parents if one of them has had Down syndrome in their family. The mosaic form of the disease (the karyotype of some cells is damaged) is formed already at the embryonic stage and does not depend on the age of the parents.
Patau syndrome
This disorder is trisomy of the thirteenth chromosome. It occurs much less frequently than the previous syndrome we described (1 in 6000). It occurs when an extra chromosome is attached, as well as when the structure of chromosomes is disrupted and their parts are redistributed.
Patau syndrome is diagnosed by three symptoms: microphthalmos (reduced eye size), polydactyly (more fingers), cleft lip and palate.
The infant mortality rate for this disease is about 70%. Most of them do not live to be 3 years old. In individuals susceptible to this syndrome, heart and/or brain defects and problems with other internal organs (kidneys, spleen, etc.) are most often observed.
Edwards syndrome
Most babies with 3 eighteenth chromosomes die soon after birth. They have pronounced malnutrition (digestive problems that prevent the child from gaining weight). The eyes are set wide and the ears are low. Heart defects are often observed.
conclusions
To prevent the birth of a sick child, it is advisable to undergo special examinations. The test is mandatory for women giving birth after 35 years of age; parents whose relatives were exposed to similar diseases; patients with thyroid problems; women who have had miscarriages.
Genetics is a science that studies the patterns of heredity and variability of all living beings. It is this science that gives us knowledge about the number of chromosomes in different types of organisms, the size of chromosomes, the location of genes on them and how genes are inherited. Genetics also studies mutations that occur during the formation of new cells.
Chromosome set
Every living organism (the only exception is bacteria) has chromosomes. They are located in every cell of the body in a certain amount. In all somatic cells, chromosomes are repeated twice, three times, or more times, depending on the type of animal or variety of plant organism. In germ cells, the chromosome set is haploid, that is, single. This is necessary so that when two germ cells merge, the correct set of genes for the body is restored. However, the haploid set of chromosomes also contains genes responsible for the organization of the entire organism. Some of them may not appear in the offspring if the second reproductive cell contains stronger characteristics.
How many chromosomes does a cat have?
You will find the answer to this question in this section. Each type of organism, plant or animal, contains a specific set of chromosomes. The chromosomes of one type of creature have a certain length of the DNA molecule, a certain set of genes. Each such structure has its own size.
And dogs - our pets? A dog has 78 chromosomes. Knowing this number, is it possible to guess how many chromosomes a cat has? It's impossible to guess. Because there is no relationship between the number of chromosomes and the complexity of the organization of the animal. How many chromosomes does a cat have? There are 38 of them.
Chromosome size differences
The DNA molecule, with the same number of genes located on it, can have different lengths in different species.
Moreover, the chromosomes themselves have different sizes. One information structure can accommodate a long or very short DNA molecule. However, chromosomes are never too small. This is due to the fact that when daughter structures diverge, a certain weight of the substance is required, otherwise the divergence itself will not occur.
Number of chromosomes in different animals
As mentioned above, there is no relationship between the number of chromosomes and the complexity of the organization of the animal, because these structures have different sizes.
The number of chromosomes a cat has is the same number of other cats: tiger, jaguar, leopard, puma and other representatives of this family. Many canids have 78 chromosomes. The same amount for domestic chicken. The domestic horse has 64, and the Przewalski's horse has 76.
Humans have 46 chromosomes. Gorillas and chimpanzees have 48, and macaques have 42.
The frog has 26 chromosomes. There are only 16 of them in the somatic cell of a pigeon. And in a hedgehog - 96. In a cow - 120. In a lamprey - 174.
Next, we present data on the number of chromosomes in the cells of some invertebrate animals. The ant, like the roundworm, has only 2 chromosomes in each somatic cell. A bee has 16 of them. A butterfly has 380 such structures in its cell, and radiolarians have about 1,600.
Data from animals show varying numbers of chromosomes. It should be added that Drosophila, which geneticists use during genetic experiments, has 8 chromosomes in somatic cells.
Number of chromosomes in different plants
The plant world is also extremely diverse in the number of these structures. Thus, peas and clover each have 14 chromosomes. Onion - 16. Birch - 84. Horsetail - 216, and fern - about 1200.
Differences between males and females
Males and females differ genetically in just one chromosome. In females this structure looks like the Russian letter “X”, and in males it looks like a “Y”. In some animal species, females have a “Y” chromosome and males have an “X”.
Traits located on such non-homologous chromosomes are inherited from father to son and from mother to daughter. The information that is fixed on the “Y” chromosome cannot pass on to the girl, because a person who has this structure is necessarily male.
The same applies to animals: if we see a calico cat, we can definitely say that this is a female.
Because only the X chromosome, which belongs to females, contains the corresponding gene. This structure is the 19th in the haploid set, that is, in germ cells, where the number of chromosomes is always two times less than in somatic ones.
The work of breeders
Knowing the structure of the apparatus that stores information about the body, as well as the laws of inheritance of genes and the characteristics of their manifestation, breeders develop new varieties of plants.
Wild wheat often has a diploid set of chromosomes. There are not many wild representatives that are tetraploid. Cultivated varieties more often contain tetraploid and even hexaploid sets of structures in their somatic cells. This improves yield, weather resistance, and grain quality.
Genetics is an interesting science. The structure of the apparatus, which contains information about the structure of the entire organism, is similar in all living beings. However, each type of creature has its own genetic characteristics. One of the characteristics of a species is the number of chromosomes. Organisms of the same species always have a certain constant number of them.
Considering our body at the cellular level, you will definitely come across its structural unit - the chromosome. It is where the genes are contained. From Greek, this concept can be literally translated as “body coloring.” Why such a strange name? The fact is that during cell division, structural units can become colored when interacting with natural dyes. The chromosome is a valuable carrier of information. Therefore, when a person develops the wrong number of chromosomes, this indicates a pathological process.
In contact with
Normal for a healthy person
According to the latest statistics, 1% of newborns today are born with abnormalities at the physiological level, when an insufficient number of chromosomes appears. This problem is already becoming global, causing great concern among doctors. A healthy person (male or female) has 46 chromosomes, that is, 23 pairs. An interesting fact is that until 1996, scientists had no doubt that there were not 23, but 24 pairs of structural units. The mistake was made by Theophilus Painter, a well-known scientist in his circle. It was found and corrected by two other luminaries - Albert Levan and Jo-Hin Tyo.
All chromosomes have the same morphological characteristics, but germ and somatic cells have a different set of structural units. What is this difference?
When cell division occurs (that is, their number begins to double), changes in chromosomes are observed at the morphological level. But, despite the fact that such complex processes occur in our body, the number of chromosomes in a person still remains the same - 46. His intellectual development and general health depend on how many pairs of chromosomes a person should have. That is why it is very important for doctors to pay attention to this issue during the pregnancy planning process. Often, the gynecologist recommends that young couples contact a geneticist who will conduct some important clinical studies.
At conception, a person receives one of the units in a pair from the biological mother, and the second from the biological father. But the sex of the unborn baby depends on the 23rd pair. When studying the human karyotype, it is important to explain that the chromosome set of healthy people consists of 22 autosomes, as well as one male and one female chromosome (the so-called sex chromosomes). A person’s karyotype can be determined without any problems by simply studying the totality of the characteristics of these units in one cell. If any abnormality is found in the karyotype, the person will face big health problems.
There can be several problems at the gene level. And all of them are considered separately, because they have a different clinical picture. Below are only those pathologies that modern medicine can successfully treat after a sick child is born:
These readings are considered a deviation from the norm and can be determined during fetal development. If it is possible that the child will be born with serious problems, doctors often recommend that the pregnant woman have an abortion. Otherwise, a woman dooms herself to life with a disabled person who will need additional education.
Abnormalities in chromosome sets
Sometimes the number of pairs does not meet the standard. A problem in intrauterine development can only be noticed by a geneticist if the expectant mother voluntarily undergoes a study. If the quantity is disturbed, then the following diseases are distinguished:
- Klinefelter's syndrome.
- Down's disease.
- Shereshevsky-Turner syndrome.
Conservative methods for replenishing the missing genetic series do not exist today. That is, such a diagnosis is considered incurable. If the problem was diagnosed during pregnancy, it is best to terminate it. Otherwise, a sick child appears with possible external deformities.
Down's disease
This disease was first diagnosed back in the 17th century. At that time, determining the number of chromosomes in a healthy person was an extremely problematic task. Therefore, the number of sick newborns was truly frightening. For every 1,000 babies, two were born with Down syndrome. After some time the illness was studied at the genetic level, which made it possible to determine how the chromosome set changes.
In Down syndrome, another pair is added to the 21st pair. That is, the total number is not 46, but 47 chromosomes. The pathology develops spontaneously, and its cause may be diabetes mellitus, the elderly age of the parents, an increased dose of radiation, or the presence of certain chronic diseases.
Outwardly, such a child differs from healthy peers. He has a narrow and wide forehead, a voluminous tongue, large ears, and his mental retardation is immediately obvious. The patient is also diagnosed with other health problems that affect many internal systems and organs.
By and large, the chromosomal sequence of the unborn baby is highly dependent on the genome of its mother. That is why before starting pregnancy planning it is necessary to undergo a full clinical examination. It will help identify hidden problems. If doctors find no contraindications, you can think about conceiving a child.
Patau syndrome
With this disorder, trisomy is observed in the thirteenth pair of structural units. This disease is much less common than Down syndrome. It occurs if an extra structural unit is attached or the structure of chromosomes and their redistribution are disrupted.
There are three main symptoms, by which this pathology is diagnosed:
- Reduced eye size or microphthalmia.
- Increased number of fingers (polydactyly).
- Cleft palate and lip.
With this disease, about 70% of infants die soon after birth (before three years of age). Children with Patau syndrome are often diagnosed with heart defects, as well as brain defects, and problems with many internal organs.
Edwards syndrome
This pathology is characterized by the presence of three chromosomes in the eighteenth pair. Most babies die soon after birth. They are born with pronounced malnutrition (they cannot gain weight due to digestive problems). They have low-set ears and wide-set eyes. Heart defects are often diagnosed.
In order to prevent the development of pathology, it is recommended that all parents who decide to conceive a child after 35 years of age undergo special examinations. There is also a greater likelihood of developing diseases in those whose parents had problems with the thyroid gland.
Do all living organisms have chromosomes? Do all mammalian cells have these structures? How many chromosomes does this or that organism have? Geneticists study such questions. Many similar questions have already been answered. Data on the number, size and shape of chromosomes are increasingly being used in other biological sciences. Particularly in taxonomy.
Chromosomes are information structures
What is a chromosome? If we examine a eukaryotic cell under high magnification, then in the normal state of this “building block” of the organism, we will not see any chromosome-like structures. They are formed only before cell division, and immediately after the end of reproduction, dense structures disappear, as if dissolving. Chromosomes are necessary for the uniform distribution of information material between daughter cells. They are formed by a DNA molecule and proteins that maintain the dense structure of the chromosome.
What is a karyotype
Each chromosome has its own size and shape. One type of organism is characterized by a certain set of chromosomes. Different individuals of the same species always have the same amount of these information structures; these structures have a size and shape characteristic of a particular species.
Thus, a karyotype is the external characteristics of chromosomes and their number in individuals of the same species. Unlike the genome, a karyotype does not include specific characteristics of individuals, but only the appearance of chromosomal structures. Karyotype features help taxonomists correctly distribute living organisms into taxonomic groups.
How many chromosomes do dogs have
Each type of organism has a certain number of chromosomes. This applies to all eukaryotes. Prokaryotes have a circular DNA molecule, which also doubles during cell division and is distributed among daughter cells without the formation of chromosomal structures.
The number of chromosomes varies extremely among different representatives of the animal and plant kingdoms. For example, a person has 46 chromosomes in somatic cells. This is a diploid set. There are 23 structures in human germ cells. How many chromosomes do dogs have? Their number cannot simply be guessed for each organism. The karyotype of a dog consists of 78 chromosomes. How many chromosomes does a wolf have in this case? Here there is a similarity in karyotype. Because all wolves are relatives to each other and to the domestic dog. Almost all wolves also have 78 chromosomes in their somatic cells. The exceptions are the red wolf and
How many chromosomes do dogs have in their reproductive cells? Germ cells always have two times fewer chromosomes than somatic cells. Because they are distributed equally between daughter cells during meiosis.
In addition to dogs and wolves, the canine family also includes foxes. There are 78 chromosomes in a dog's karyotype. How many chromosomes do foxes have? Taxonomic genera of foxes are very heterogeneous in the number of chromosomes. The common fox has 38. The sand fox has 40. The Bengal fox has 60.
How many chromosomes are there in a dog's red blood cells?
Red blood cells are red blood cells that serve as oxygen carriers. How are they structured? Mature red blood cells must contain a large amount of hemoglobin. That is why they do not have many organelles, including chromosomes, since there is no nucleus at all.
However, in the blood of dogs, as in the blood of humans, there are reticulocytes - immature red blood cells. They make up only 1-2 percent of the total number of red blood cells. Reticulocytes contain ribosomal RNA, mitochondria, ribosomes, and the Golgi complex. But after a day or a day and a half, reticulocytes are transformed into mature red blood cells, which do not contain DNA, and, consequently, chromosomal structures.
How many chromosomes are in the karyotype of other animals
Animal species are very diverse in karyotype. Moreover, the number of chromosomes in the nuclei of cells of various animals does not depend on the complexity of the organization of a living being. For example, in a somatic cell of a frog there are 26 chromosomes. Chimpanzees have 48, which is slightly more than humans. Domestic chicken has 78 structures. This is the same number of chromosomes in dogs. The carp has 104, and the lamprey, a jawless vertebrate, has 174.
Chromosome set of plants
The karyotype of plant forms is also extremely diverse. Bread wheat with a hexaploid set of chromosomes has 42 information structures, rye has 14, and corn has 20. Tomatoes have 24 chromosomes in each cell, and rice has the same number. Jerusalem artichoke has 102.
There are absolute record holders in the number of chromosomes in the plant kingdom. These are ferns.
There are about 1200 chromosomes in the cell of this ancient plant. Horsetail has many such structures: 216.
Thus, all eukaryotic cells, except erythrocytes, have chromosomes. Depending on the type of animal or plant, the quantitative composition of chromosomes changes, as well as their size and shape. It is precisely because chromosomes have different sizes that the number of these structures is so different. The smaller the structures, the more likely their number will be greater.
