The chromosomes

What are chromosomes ?
Chromosomes are microscopic structures ,rod- shaped ,filamentous bodies present in the nucleus of cells in the body (except for red blood cell) ,which become visible during cell division . They are the carriers of the gen or unit of heredity . Chromosomes are not visible in active nucleus due to their high water content ,but are clearly seen during cell division .
Chromosomes in eukaryotes and prokaryotes are different
EUKARYOTES
PROKARYOTES
many chromosomes
single chromosome plus plasmids
linear chromosomes
circular chromosome
made of chromatin, a nucleoprotein (DNA coiled around histone proteins)
made only of DNA
found in a nucleus
found in cytoplasm
copies chromosomes, then the cell grows, then goes through mitosis to organise chromosomes in two equal groups
copies its chromosome and divides immediately afterwards.Strecture of chromosomes
? Chromosomes are composed of thin chromatin threads called Chromatin fibrs .
? These fibers undergo folding, coiling and supercoiling during prophase so that the chromosomes become progressively thicker and smaller.
? Therefore, chromosomes become readily observable under light microscope .
? At the end of cell division, on the other hand, the fibers uncoil and extend as fine chromatin threads, which are not visible at light microscope.