The term ' chromosome ' comes from the Greek chroma ( colour ) and soma
( body ). Scientists coined the term because chromosomes are cell structures , or bodies , that were found to be strongly stained by certain colourful dyes during research .
CHROMOSONE STRUCTURE
Chromosomes vary in number and shape among living things . Most bacteria have one or two circular chromosomes . Humans , along with plants and other animals , have linear chromosomes that are arranged in pairs within the nucleus of the cell .
Each chromosome , in its nonreplicated state , consists of a single chromatid , which is simply a very long DNA molecule to which are attached a great many ‘ histone protein molecule complexes ’. Histones make up about 40 percent of every chromosome while DNA accounts for the other 60 percent . Once duplicated , every chromosome consists of two identical copies of itself , called sister chromatids .
> The centromere is the constricted region of a linear chromosome at which point sister chromatids are attached . It also separates the chromosome into a short arm ( p ) and a long arm ( q ). Centromeres help keep chromosomes properly aligned during cell division . The centromere can be located at different positions along the chromosome , resulting in four different types of chromosomes :
Metacentric The centromere is in the middle , meaning the p and q arms are of equal length ( chromosomes 1 , 3 , 16 , 19 , 20 ).
Submetacentric The centromere is off-center , leading to a shorter p arm and a longer q arm ( chromosomes 2 , 4-12 , 17 , 18 , X ).
Acrocentric The centromere is severely offset from the center , leading to a much shorter p arm ( chromosomes 13-15 , 21 , 22 , Y ).
Telocentric The centromere is found at end of the chromosome , meaning no p arm exists ( not found in humans ).