1. Pellicle: Chromosomes are covered by a membrane called pellicle. Modern studies have found no attachment to the pellicle. Scientists Mc Clinton and Swanson mentioned the pellicle. But scientists Darlington, Novikoff and Rees deny Pellicol’s existence.
2. Matrika: The fluid inside the pellicle is called Matrika. But the remains of the mother have not been found till date.
3. Centromere: The word Centromere is formed from the Greek word Kentron meaning center and meros meaning part. The round, colorless and constricted area in the chromosome is called centromere. Each chromosome has only one centromere. However, some chromosomes may have two or more centromeres. The position of the centromere creates a groove in the chromosome. This is called Mukhyakunchan or Mukhyakhan. Scientist Darlington named it centromere.
4. Kinetochore: The disc or disk like structure at the centromere of chromosome is called kinetochore. The kinetochore contains DNA, tubulin protein and microtubules. Each kinetochore is composed of two plates. The outer plate is associated with microtubules and the inner plate with centromeric heterochromatin. It regulates chromosomal movement.
5. Arms: The chromosomal parts on either side of the centromere are called arms. Chromosome arms can be equal or unequal.
6. Secondary Contractions: Chromosomes contain one or more other sites of contraction other than the centromere. This is called secondary shrinkage. A secondary contraction called SAT (Sine Acid Thymonucleic) forms the nucleolus. Each diploid chromosome has a pair of secondary chromosomes. It is called Nucleolar Organizer Region-NOR. Human chromosomes 13, 14, 15, 21 and 22 have a total of five pairs of NORs.
7. Chromomeres: The small beads like beads found in the chromosomes are called chromomeres. Its other name is Idiomere. Chromomeres are formed by DNA coiling. The region between two chromomeres is called interchromomeres.
8. Satellite: The small segment adjacent to the secondary end of the chromosome is called satellite. Such chromosomes are called SAT chromosomes. Chromosome 1 of chickpea has satellite. Human chromosomes 13, 14, 15, 21 and 22 have been identified as SAT chromosomes. Cotton and jute have satellite chromosomes.
9. Telomere: The word Telomere is formed from the Greek words telos meaning end and meros meaning part. Scientist H. J. According to Müller, the characteristic regions at both ends of chromosomes are called telomeres. The repeated sequence of DNA at the head of the chromosome is the telomere. Because of telomeres, chromosome arms can never come together. Here some nucleotides are rearranged. It contains the telomerase enzyme that works to prevent human aging. Telomere length decreases with each cell division. Therefore, the age of an organism can be determined by measuring the length of the telomere. Human telomere length is 8000 base pairs at birth, 3000 base pairs at age 35, and 1500 base pairs at age 65. Telomeres are always in the TTAGGG state in higher plants and TTTAGGG in vertebrates. The function of telomeres is to protect the coding region of DNA from destruction during cell division.
10. Chromatin: Each chromosome divides longitudinally to form two thread-like structures. These are called chromatin. It is initially 11 nm thick and gradually becomes 30 nm, 300 nm and 700 nm thick. Heitz (1928) divided chromatin fibers into two parts. Heterochromatin and Euchromatin.
11. Chromonema: Each chromatid divides longitudinally to form two linear structures. It is called chromonema. Scientist Vejdovsky (1921) called them Chromonema. Chromonema has two types of patches. Paranemic panch and plactonemic panch. Each chromoneme is made up of 26 or 32 molecules. However, in 1965, scientist Drup proved that chromonema does not have any formula. During the anaphase phase the chromatin becomes organized into chromosomes.
