CHROMOSOMES

CHROMOSOMES
During cell division chromatin material becomes shorter and thicker forming chromosomes, chromosomes stains dark and under compound microscope appears to be made up of arms and centromeres.
Centromeres attached the two arms called chromatids. Centromeres has a proteins called kinetochore proteins through which chromosomes is attached to the spindle fibers during cell division.

COMPOSTION OF CHROMOSOMES:
A chromosomes is composed of DNA and proteins. (one chromosomes =one DNA molecules)

DIPLOID AND HAPLOID NUMBER OF CHROMOSOMES
The full number of chromosomes in normal body cells is diploid (2n) whereas haploid (n) is the half number of chromosomes present in germ or gamete cells. For example, human sperms and eggs have 23 each and those of Drosophila have 4 each in sperms and eggs. So in this way after fertilization the number of chromosomes remains constant in the next generation

EUCHROMATIN:
Euchromatin is the well dispersed form of chromatin which takes lighter DNA-stain and is genetically active, i.e. it is involved in gene duplication, gene transcription (DNA- dependent RNA synthesis) and morphological expression of a gene through some type of protein synthesis.

HETEROCHROMATIN:
Heterochromatin is the highly condensed form of chromatin which takes dark DNA-stain and is genetically inert. Such type of chromatin exists both in the region of centromere (called constitutive heterochromatin) and in the sex chromatin (called facultative heterochromatin) and is late replicating one.