How many chromosomes a person has?
Chromosome is a structural-functional elementcell nucleus containing genes. The name "chromosome" comes from the Greek words (chrōma - color, color and sōma - body), and is due to the fact that during cell division they intensively stain in the presence of basic dyes (for example, aniline).
Many scientists, from the beginning of the XX century, thought aboutquestion: "How many chromosomes a person has?". So until 1955, all the "minds of mankind" were convinced that the number of chromosomes in man is 48, i.е. 24 pairs. The reason was that Teofilus Painter (a Texas scientist) incorrectly counted them in preparative sections of the testes of people who were castrated by court decision (1921). Later, other scientists, using different methods of counting, also came to this opinion. Even after developing the method of separation of chromosomes, the researchers did not challenge the result of Painter. The error was discovered by scientists Albert Levan and Joe-Hin T'o in 1955, who accurately calculated how many pairs of chromosomes a person had, namely, 23 (they used more modern techniques when calculating them).
Somatic and sex cells contain differentchromosome set in biological species, which can not be said about the morphological features of chromosomes, which are constant. Somatic cells have a doubled (diploid set), which is divided into pairs of identical (homologous) chromosomes, which are similar in morphology (structure) and magnitude. One part is always paternal, the other is of motherly origin. Sexual cells of a human (gametes) are represented by a haploid (single) set of chromosomes. When the ovum is fertilized, they unite in one nucleus of the zygote of haploid sets of female and male gametes. This recovers the double set. You can tell exactly how many chromosomes a person has - 46, with 22 pairs of them being autosomes and one pair - sex chromosomes (gonosomes). Sexes have differences - both morphological and structural (composition of genes). In the female body, the gonosome pair contains two X chromosomes (XX pair), and in the male body, one X and Y chromosome (XY pair).
Morphologically, chromosomes change in divisioncells when they are doubled (with the exception of sex cells, in which doubling does not occur). This is repeated many times, but the change in the chromosome set is not observed. Most noticeable are chromosomes at one of the stages of cell division (metaphase). In this phase, the chromosomes are represented by two longitudinally-split formations (sister chromatids) that narrow and unite in the area of the so-called primary constriction, or centromeres (an obligatory element of the chromosome). Telomeres are called the ends of the chromosome. Structurally, human chromosomes are represented by DNA (deoxyribonucleic acid), which encodes the genes that make up their composition. Genes, in turn, carry information about a particular feature.
On how many chromosomes a person will haveits individual development depends. There are such concepts as: aneuploidy (change in the number of individual chromosomes) and polyploidy (the number of haploid sets is more diploid). The latter can be of several types: loss of homologous chromosome (monosomy), or appearance of extra chromosomes (trisomy - one extra, tetrasomy - two extra, etc.). All this is a consequence of genomic and chromosomal mutations, which can lead to such pathological conditions as: Down's disease, Kleinfelter syndrome, Shereshevsky-Turner syndrome and other diseases.
Thus, only the twentieth century gave answers to allquestions, and now about how many chromosomes a person has, every educated inhabitant of the planet Earth knows. It is on the composition of the 23 pairs of chromosomes (XX or XY) that the sex of the unborn child depends, and this is determined by the fertilization and fusion of the female and male sexual cells.
