Chromosomal aberrations are of two
types.
1. Euploidy:
Addition or removal of a complete set of chromosome
2. Aneuploidy:
Addition or removal of individual chromosome
Euploidy
In euploidy an organism acquires an additional
set of chromosomes over and above the diploid complement, eg. Triploidy (3n),
Tetraploidy (4n), Pentaploidy (5n),
hexaploidy (6n).
|
Euploids
|
Constitution
|
No
of chromosomes
|
|
Monoploids (n)
|
XYZ
|
3
|
|
Diploid (2n)
|
XX YY ZZ
|
6
|
|
Triploid (3n)
|
XXX YYY ZZZ
|
9
|
|
Tetraploid (4n)
|
XXXX YYYY ZZZZ
|
12
|
Euploidy again can be divided into
two Autopolyploidy and Allopolyploidy.
Autopolyploidy
The source of extra
chromosome is same species. Auto polyploidy can be autotriploidy or
autotetraploidy. Autotriploids are formed as a result of fusion of gametes of
tetraploids and diploid. Although sterile, once formed these plants are robust
and can be propagated through asexual reproduction methods.
Autopolyploidy is observed in nature as well
as it can be induced also. Treating the deviding cells with colchinice arrest
the spindle formation and prevents the migration of chromosome to the poles. As
a result, one of the progenies will be with 4n number.
Allopolyploidy
An allopolyploid is a plant
that is a hybrid of two or more species, containing two or more copies of each
of the input genomes. Eg. Raphnobrassica
(4n 18+18) is a hybrid of Raphnus sativus,2n 18 (Radish) and Brassica
oleracea, 2n 18 (Cabbage).
Polyploids are very important in agriculture.
Important example is Wheat. Commonly used wheat variety (Tritium aestivum,
hexaploid, 2n = 42) is developed from goat grass (2n 14) and T. dicoccum (2n
28).
Assignment: Make a list of polyploidy plants
used for cultivation.
