Chromosomes Each person's genetic information is stored in 23 pairs of chromosomes, which vary greatly in size and shape. Chromosome 1 is the largest, more than three times the size of chromosome 22. The twenty-third pair of chromosomes are two special chromosomes, X and Y, which determine our sex. Women have a pair of X chromosomes (46, XX), while men have a pair of X and Y chromosomes (46, XY).
The main component of each chromosome is DNA, and genes are the main components of chromosomal DNA. The molecule of each chromosome is very long, so for compactness it is tightly wound on specific histone proteins. This phenomenon is called supercoiling or supercompaction.
Almost in the center of each chromosome is its centromere, a small area that divides the chromosome into two parts, forming a long arm (q) and a short arm (p). In addition, for a more detailed and accurate study of chromosomes, the method of staining chromosomes with special dyes is used. The use of which causes the formation of a characteristic striped structure. Each chromosome has a unique clear striped structure, and each strip has a number that helps to identify (localize) a specific part of the chromosome (locus). This method, in which the position of a particular gene is determined by its location on a specific strip of the chromosome, is called cytogenetic mapping. For example, the beta-hemoglobin (HBB) gene is located on chromosome 11p15.4. This means that the HBB gene is located on the short arm (p) of chromosome 11 and is located on band 4 of the 15th region of this chromosome.
The emergence of new methods of DNA analysis makes it possible to study the structure of chromosomes in more detail. The method of cytogenetic mapping can be called a bird's eye view in relation to the techniques that are currently available for genetic research. Thus, the main goal of the well-known Human Genome Project is to identify and determine the sequence of more than 30,000 human DNA genes.
Karyogram of a man
This is an image of 23 pairs of human chromosomes. They are colored and arranged in decreasing order of size. The presence of a Y chromosome in the last pair indicates that this set of chromosomes is male. |
For comparison, you can imagine that all the DNA contained in the nucleus of each cell in its unwound form would be about three meters long. If we calculate the length of all the DNA in the human body, then if these strands are added together, this double strand could connect the Earth and the Sun about 70 times. The length of DNA of one chromosome is on average 5 cm.