Chromosomes
Each cell contains a nucleus within which there are several thread-like structures known as chromosomes, so called because of their affinity for certain stains. (Chroma = color soma = body (
Chromosome: is DNA thread-like double-helix tightly coiled around histones.
Human somatic cells have 23 pairs of chromosomes (diploid number), with one copy of each chromosome inherited from each parent:
ü 22 pairs of chromosomes are autosomes;
ü The remaining pair is called the sex chromosomes (XX in female or XY in male).
Human genetic material contains 3.1 billion bases.
Each germ cell contains 23 single chromosomes (haploid number):
ü 22 autosomes +
ü 1 sex chromosome ( x in ovum - Y or X in sperm)
The non-dividing chromosome appears as thread-like structure which has:
· Short arm (p) (for ‘petit’ or small)
· constriction (centromere): localize genes and categorize chromosomes.
· Long arm (q) (as next letter in the alphabet!) .
