Describe the structure of chromosomes with a suitable diagram.
Chromosomes are filamentous bodies present in the nucleus and are visible during cell division. A metaphasic chromosome has 2 identical halves called sister chromatids. Each chromatid is in turn made up of sub chromatids called chromonemata (singular – chromonema). The chromatids lie side by side and are held together at one point called the centromere. The centromere is also called the primary constriction. During cell division, the spindle fibres are attached at the centromere. Besides the primary constriction, additional narrow areas called secondary constrictions are present. Some of the secondary constrictions are called nucleolar organizers because they are necessary for the formation of the nucleolus. The part of the chromosome beyond the nucleolar organizer is short, spherical and is called satellite. The tip of the chromosome is called telomere. It has a unique property in that it prevents the ends of the chromosomes from sticking together but attaches to the nuclear envelope. The surface of a chromosome bears the number of small swellings called chromosomes.
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- Inheritance of Two Genes - Chromosome Theory of Inheritance