Brief note on Chromosomes

Chromosomes

Table of Contents

WHAT ARE CHROMOSOMES

Chromosomes are thread like structures which are made of protein and DNA which can be found inside the nucleus of animal and plant cells.

According to the position of the centromere there are 4 main types of chromosomes.
1) Metacentric
2) Sub metacentric
3) Acro centric
4) Telocentric

CHEMICAL STRUCTURE OF CHROMOSOMES

Chemically chromosomes are formed of nucleic acid and protiens. About 90% are De-oxy Ribonucleo protiens. The remaining 10% constitutes the residual chromosome. The DNA protiens are formed of 45% DNA and 45% basic protiens, the hsitone.

The residual chromosome is the substance of the chromosome remaining after the removal of DNA and histone. The residual chromosome contains RNA, DNA and residual protien. The residual protien is acidic in nature, which forms the structural integrity of the chromosome. If the residual protien is removed, the structural integrity of the chromosome is lost. Removal of DNA and histones doesn’t affect the structural integrity. There is another special type of protien called as chromosmin formed of high tryptochan. The linkage between the DNA and protien is of ionic nature and is called salt linkage. Specific divalent ions namely Ca++, Mg++, Fe++ present in cells formed additional linkages in the chromosomes between DNA and Protien or between DNA groups.

FUNCTION OF CHROMOSOMES

1) They control the heredity. They carry genes feom parents to young ones.
2) The chromosomes control the metabolism of an organism.
3) The hetero Chromatin helps in the formation of nucleolous.
4) Chromosomes control the differentiation of different characteristics of an organism.
5) Changes in the number and the structure of chromosomes lead to the formation of New species.

SPECIAL TYPES OF CHROMOSOMES

In addition to the normal types of chromosomes special types of chromosomes with different structure, shape and functions are found in varied groups of animals and plants l. These are very useful in cytogenetic studies. The most important are giant chromosomes and suoer numerary chromosomes. These are exceptionally larger chromosomes. They are described as unusual chromosomes by A. M. Winchester. There are 2 types of giant chromosomes:-
i) Polytin chromosome,
ii) Lambbrush chromosome.