# Describe the structure of chromosome.
ANS :
* Chromosomes are carriers of genes.
* Chromosomes can be identified by staining.
* In prokaryotes only one chromosome occurs whereas in eukaryotes many chromosomes occur in pair.
* The paired structure of chromosomes is known as diploid(2n) and is seen in somatic cells. They are called homologous chromosomes as both the chromosomes of a pair are exactly similar.
* The number of diploid chromosomes is fixed for a species.
* In reproductive cells the chromosomes are haploid(n), i.e. they are half in number.
* During cell division(metaphase), different chromosomes get separated from each other and their morphological study becomes possible.
* A group of minimum two chromatids forms one chromosome.
* The diameter of each chromatid is 60 A°.
* Chromatids are joined with each other by a dark region called centromere or primary constriction. Some chromosomes have additional secondary constriction.
* Variation can be seen in position and number of centromere.
* The length of chromosomes is 0.2 - 5.0μ (micron) andtheir diameter ranges from 0.2 - 2.0μ.
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