- Organism with single genome, i.e., ‘A’ – haploid.
- Organism with two similar genomes, i.e., ‘AA’ –
autodiploid. - Organism with three similar genomes, i.e., ‘AAA’ –
autotriploid. - Organism with four similar genomes, i.e., ‘AAAA’ –
autotetraploid and so on.
• Autopolyploids are present naturally and can also be
produced artificially.
• Natural autopolyploids are found in apple, banana,
doob grass (Cynodon dactylon), grapes, tomato,
watermelons, Oenothera, maize, barseem, marigold,
etc.
• Polyploidy can be induced artificially by colchicine
treatment in 0.01–0.5% concentration.
• Colchicine is an alkaloid obtained from seeds and
corms of Colchicum autumnale, a plant belonging
to family Liliaceae (first obtained by Houde, 1887
and was first used for inducing polyploidy by Dustin,
1934).
• Colchicine induces cell division without cytokinesis
(cell wall formation), because of its property of
arresting and breaking the spindle. Thus, doubling
of chromosome number occurs.
• Colchicine treatment for inducing polyploidy can be
given in either of the following ways :
(i) By soaking seeds in its solution.
(ii) By placing cotton soaked in colchicine solution
on axillary bud.
(iii)By injecting colchicine solution into the
seedlings.
• Colchicine has no effect on its parent plant
(Colchicum), because of presence of anticolchicine
in it (Blakeslee).
• Colchicine also has medicinal property, and is used
to cure rheumatism.
(ii) allopolyploidy
• This is a chromosomal variation produced in crosses,
between two species, having different sets of
chromosomes.
• The resulting hybrid has a different number of
chromosomes, than the parents.
• For example :
• Some classical examples of allopolyploids are:(a) raphanobrassica
• This allopolyploid was produced by G.D. Karpechenko
(1927) by doubling the chromosome number of
F 1 hybrid produced by crossing radish (Raphanus
sativus) and cabbage (Brassica oleracea).
• This cross was made to produce a new plant with
root character like radish and stem character like
cabbage, i.e.,• But it has no agricultural importance because the roots
of this new plant were like cabbage and stem like
radish.(b) triticale or triticosecale
• This is first man made crop or cereal, produced
by Rimpau.
• Triticale is an example of artificial allopolyploid,
produced by crossing wheat (Triticum) and European
rye (Secale), i.e., intergeneric hybridization.
• Triticale may be hexaploid, or octaploid, on the basis
of wheat used in hybridization (i.e., tetraploid wheat
or hexaploid wheat).