What is a chromosome? A set of chromosomes. Pair of chromosomes

Heredity and variability in living nature exist due to chromosomes, genes, deoxyribonucleic acid (DNA). The genetic information in the form of a chain of nucleotides in the DNA is stored and transmitted. What role does genes play in this phenomenon? What is a chromosome in terms of transmission of hereditary traits? Answers to such questions allow us to understand the principles of coding and genetic diversity on our planet. In many ways, it depends on how many chromosomes are included in the recruitment, from the recombination of these structures.

From the history of the discovery of "particles of heredity"

Studying the cells of plants and animals under a microscope, many botanists and zoologists in the middle of the XIX century drew attention to the thinnest threads and the smallest ring-shaped structures in the nucleus. Most often, the discoverer of chromosomes is the German anatomist Walter Flemming. It was he who used aniline dyes to process nuclear structures. The discovered substance Flemming called "chromatin" for its ability to stain. The term "chromosomes" in 1888 was introduced into the scientific revolution by Henry Valdeier.

Simultaneously with Flemming, I sought an answer to the question of what a chromosome is, a Belgian Edward van Beneden. Hardly earlier, German biologists Theodore Boveri and Edward Strasburger conducted a series of experiments demonstrating the individuality of chromosomes, the constancy of their number in different species of living organisms.

Preconditions of the chromosome theory of heredity

American researcher Walter Sutton found out how many chromosomes are contained in the cell nucleus. The scientist considered these structures as carriers of heredity units, signs of an organism. Sutton found that the chromosomes consist of genes, through which properties and functions are transmitted to descendants from parents. The geneticist in his publications gave descriptions of chromosome pairs, their movements in the process of cell nucleus division.

Regardless of his American counterpart, the work in the same direction was led by Theodore Boveri. Both researchers studied the problems of the transmission of hereditary traits in their works, formulated the main provisions on the role of chromosomes (1902-1903). Further development of the Boveri-Sutton theory took place in the laboratory of Nobel laureate Thomas Morgan. An outstanding American biologist and his assistants established a number of patterns of gene placement in the chromosome, developed a cytological basis that explains the mechanism of the laws of Gregor Mendel, the founding father of genetics.

Chromosomes in a cage

The study of the structure of chromosomes began after their discovery and description in the XIX century. These bodies and threads are contained in prokaryotic organisms (non-nuclear) and eukaryotic cells (in nuclei). The study under the microscope made it possible to establish that such a chromosome is from a morphological point of view. This is a movable threadlike body, which is discernible in certain phases of the cell cycle. In the interphase, the whole volume of the nucleus is occupied by chromatin. In other periods, the chromosome is distinguishable as one or two chromatids.

It is better to see these formations during cell division - mitosis or meiosis. In eukaryotic cells, larger chromosomes of linear structure are more often observed. They have less prokaryotes, although there are exceptions. Cells often include more than one type of chromosome, for example, their own small "hereditary particles" are in mitochondria and chloroplasts.

Forms of chromosomes

Each chromosome has an individual structure, differs from other features of staining. In the study of morphology, it is important to determine the position of the centromere, the length and placement of the arms relative to the waist. The set of chromosomes usually includes the following forms:

• Metacentric, or equilateral, for which the middle position of the centromere is characteristic;
• Submetacentric, or non-equilibration (the constriction is biased towards one of the telomeres);
• Acrocentric, or rod-shaped, in which the centromere is located almost at the end of the chromosome;
• Point with a form that is difficult to define.

Chromosome functions

Chromosomes consist of genes - functional units of heredity. Telomeres are the ends of the shoulders of the chromosome. These specialized elements serve to protect against damage, prevent the coalescence of fragments. The centromere performs its tasks when doubling the chromosomes. It has a kinetochore, it is to it that the structures of the spindle of division are attached. Each pair of chromosomes is individual at the location of the centromere. The threads of the division spindle work in such a way that one chromosome departs into the daughter cells, and not both. Uniform doubling in the division process provides the origin of replication. The duplication of each chromosome begins simultaneously in several such points, which significantly accelerates the entire process of fission.

The role of DNA and RNA

It is possible to find out what the chromosome is, what function this nuclear structure performs, after studying its biochemical composition and properties. In eukaryotic cells, nuclear chromosomes are formed by a condensed substance - chromatin. According to the analysis, its composition includes high-molecular organic substances:

• Deoxyribonucleic acid (DNA);
• Ribonucleic acid (RNA);
• Proteins-histones.

Nucleic acids take a very direct part in the biosynthesis of amino acids and proteins, ensure the transfer of hereditary characteristics from generation to generation. DNA is contained in the nucleus of the eukaryotic cell, RNA is concentrated in the cytoplasm.

Genes

X-ray diffraction analysis showed that DNA forms a double helix, whose chains consist of nucleotides. They are a carbohydrate deoxyribose, a phosphate group and one of four nitrogen bases:

1. A is adenine.
2. D is guanine.
3. T is thymine.
4. C is cytosine.

Areas of spiral deoxyribonucleoprotein filaments are genes carrying coded information on the sequence of amino acids in proteins or RNA. During reproduction, hereditary traits from parents to offspring are transmitted in the form of gene alleles. They determine the functioning, growth and development of a particular organism. According to a number of researchers, those parts of DNA that do not encode polypeptides perform regulatory functions. The human genome can number up to 30 thousand genes.

Set of chromosomes

The total number of chromosomes, their features - a characteristic feature of the species. In Drosophila flies, their number is 8, in primates 48 and in humans 46. This number is constant for the cells of organisms that belong to the same species. For all eukaryotes there is the concept of "diploid chromosomes". This is a complete set, or 2n, in contrast to the haploid - half amount (n).

Chromosomes in a single pair are homologous, identical in shape, structure, location of centromere and other elements. Homologues have their own characteristics, which distinguish them from other chromosomes in the set. Staining with basic dyes allows to examine, to study the distinctive features of each pair. The diploid set of chromosomes is present in somatic cells, while the haploid set is present in sexual (the so-called gametes). In mammals and other living organisms with heterogametic male sex, two kinds of sex chromosomes are formed: the X chromosome and the Y. The males have a set of XY, the females have XX.

Chromosomal recruitment of a human

The cells of the human body contain 46 chromosomes. All of them are combined into 23 pairs that make up the set. There are two types of chromosomes: the autosomes and the sex. The first form 22 pairs - common for women and men. They are distinguished by the 23rd pair - sex chromosomes, which in the cells of the male body are nonhomologous.

Genetic traits are associated with gender. For their transmission, Y and X chromosomes are used in men, two X in women. Autosomes contain the remainder of information on hereditary traits. There are techniques that allow to individualize all 23 pairs. They are clearly distinguishable in the drawings, when painted in a certain color. It is noticeable that the 22nd chromosome in the human genome is the smallest. Its DNA in the stretched state has a length of 1.5 cm and has 48 million pairs of nitrogenous bases. Special proteins of histones from the chromatin make compression, after which the thread takes up thousands of times less space in the nucleus of the cell. Under an electron microscope, the histones in the interphase nucleus resemble beads strung on a DNA strand.

Genetic diseases

There are more than 3 thousand hereditary diseases of different types, caused by damage and disorders in the chromosomes. Down syndrome is one of them. For a child with such a genetic disease, a lag in mental and physical development is characteristic. In cystic fibrosis, there is a failure in the functions of the glands of external secretion. Violation leads to problems with perspiration, secretion and accumulation of mucus in the body. It complicates the work of the lungs, can lead to suffocation and death.

Disorder of color vision - color blindness - immunity to some parts of the color spectrum. Hemophilia leads to a weakening of blood coagulability. Lactose intolerance does not allow the human body to absorb milk sugar. In family planning offices, one can learn about the predisposition to a particular genetic disease. In large medical centers, it is possible to undergo the appropriate examination and treatment.

Genotherapy - the direction of modern medicine, the elucidation of the genetic cause of hereditary diseases and its elimination. With the help of new methods, normal genes are introduced into pathological cells instead of disturbed ones. In this case, doctors relieve the patient not of symptoms, but of the causes that caused the disease. Only the correction of somatic cells is carried out, the methods of gene therapy are not yet applied massively to the sex cells.