In a dividing cell, the hereditary material is compactly packed. Due to DNA helixing during cell division, the hereditary material becomes visible under a light microscope as rod-shaped bodies – chromosomes.
Chromosomes have shoulders and the primary constriction is the centromere. Before DNA doubling, the chromosome is formed by one DNA molecule, and after reduplication it includes two DNA molecules – chromatids bound in the centromere region. The shape of the chromosomes depends on the primary constriction, to the area of which, during division of the cell, the threads of the division spindle are attached. The centromere divides the chromosome into 2 shoulders. There are 3 main types of chromosomes:
1) equal shoulders – with shoulders of equal or almost equal length;
2) unequal shoulders – with shoulders of different lengths;
3) rod-shaped – with one long, I have another very short shoulder.
Some chromosomes have a secondary constriction — a region of lesser spiralization of the chromosome material corresponding to the position of the nucleolar organism in it.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.