Numerical changes in chromosome can be of two types
- Aneuploidy
- Euploidy
Aneuploidy
The loss or gain of one or few chromosomes as compared to the somatic chromosome number of a species is called as aneuploidy.
It is of following types
- Monosomy
- Nullisomy
- Trisomy
- Tetrasomy
Monosomy (2n – 1)
One chromosome is missing from the somatic chromosome complement
Nullisomy
One pair of chromosome is missing from the somatic chromosome complement
Double monosomic state (2n -1 -1) when two missing chromosomes are non-homologous
Trisomy (2n +1)
When somatic cell of an organism contain three copies of any one chromosome of the haploid complement
- Primary trisomics
- Secondary trisomics
- Tertiary trisomics
Tetrasomy(2n + 2)
When somatic cell of an organism contain one pair of chromosome in addition to the somatic complement.
Euploidy
Have one or more complete genomes which may be identical with or distinct from each other.
Monoploids (including haploids)
Monoploidy (x) – denotes presence of a single copy of a single genome
Haploidy (n) – represent gametic chromosome number of a species irrespective of whether it is diploid or polyploid species.
Polyploids
Presence of more than two genomes in an individual
Polyploids can be of two types as follows
Autopolyploidy
Have multiple copies of same genome.
Allopolyploidy
Contain two or more distinct genome derived from different species.