Write a note on polyploidy.

Explanation

Polyploidy is the condition where an organism possesses more than two basic sets of chromosomes.
It is an important factor in the origin of new plant species. But higher ploidy level leads to death. Polyploidy is of two types, (i) Autopolyploidy and (ii) Allopolyploidy.
(i) Autopolyploidy
The organism which possesses more than two haploid sets of chromosomes derived from within the same species is called autopolyploid. They are divided into two types. Autotriploids and autotetraploids.
(ii) Autotriploids have three set of its own genomes. They can be produced artificially and are highly sterile due to defective gamete formation.
Example: The cultivated banana are usually triploids and are seedless having larger fruits than diploids. Seedless watermelon, apple, sugar beet, tomato, banana are man made autotriploids.
(iii) Autotetraploids have four copies of its own genome. They may be induced by doubling the chromosomes of a diploid species.
Example: rye, grapes, alfalfa, groundnut, potato and coffee.
(iv) Allopolyploids: An organism which possesses two or more basic sets of chromosomes derived from two different species is called allopolyploid. It can be developed by interspecific crosses and fertility is restored by chromosome doubling with colchicine treatment. Allopolyploids are formed between closely related species only.
Eg: Parents
Raphanus `xx` Brassica
2n=18 2n=18
Sterile `F_(1)` hybird
(n+n)=9+9
(2n)=18
Fertile amphidiploid `rArr` Raphano brassica
2n = 4x = 36
(v) Triticale, the successful first man made cereal. Depending on the ploidy level Triticale can be divided into three main groups.
(a) Tetraploidy
(b) Hexaploidy
(c) Octoploidy
Hexaploid Triticale combines the high- protein content of wheat with rye's high content of the amino acid lysine, which is low in wheat.