Chromosome number

Chromosome number in every species is generally constant. In higher organisms, the number
of chromosomes in a somatic cell is called somatic number irrespective of the ploidy level
(number of basic chromosome set) and is represented by 2n.

In the gametes, the chromosome number is reduced to half, it is known as the gametic number or
haploid number and is represented by “n”.

Some organisms including many plants have three or more sets of chromosomes and are
referred to as polyploid. The basic chromosome number is denoted by “x” so that the
chromosome number of a diploid cell or individual is expressed as “2x”.

Diploid: 2n = 2x, n = x
Tetraploid: 2n = 4x, n = 2x
Hexaploid: 2n = 6x, n = 3x



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