POLYPLOIDY AND ITS NEED AND ROLE IN CROP
* POLYPOIDY
* Polyploidy is defined as state in which a normal organism or diploid cells have more than two homologous sets of chromosomes in polyploidy there is a more than double the haploid number of chromosomes.
* Organisms having multiple sets of chromosomes instead of basic or diploid number of chromosomes are called POLYPLOIDS ORGANISMS.
* Types of polyploidy
Two types of polyploidy
Euploidy
* Aneuploidy
* Euploidy
Multiplication of whole or complete set of chromosomes or the change in number of chromosomes is the exact multiple of basic number of chromosomes.
* Types of euploidy
On the basis of composition of genome
* Autopolyploidy
* Allopolyploidy
* Autopolyploidy
When change in the number of chromosome is the exact multiple of a single Genome of specific species.
Examples
* Tetraploid crops (alfalfa , peanut, potato coffee)
* Allopolyploidy
When change in the number of chromosome has increased by combining two or more different genomes of different species.
It may be the result of non disjunction.
Examples
Strawberry, Wheat and Oil seed Rape.
* ANEUPLOIDY
When there is addition or subtraction of one or more specific chromosomes to the basic number of chromosomes.
When change in the number of chromosomes is the not exact multiple of basic number of chromosomes..
* CLASSIFICATION OF ANEUPLOIDY
* MONOSOMY
WHEN ONE CHROMOSOME IS MISSING FROM THE ANY ONE PAIR OF THE GENOME
2n-1
Monosomic Gossipium hirsutum
* NULLISOMY
When complete pair of chromosomes is missing from the basic number of chromosomes
2n-2
* Trisomy
When there is addition of extra number of chromosomes to the basic number of chromosomes
2n+1
Example
Datura
* Tetrasomy
When there is addition of additional pair of chromosomes to the basic number of chromosome.
2n+2
Example
Potato 4X=48
* NEED AND ROLE OF POLYPLOIDY
* Polyploidy plays important role in the plant evolution
* Polyploidy is needed to produce
* Superior progeny,
* Bigger size plants,
* Double the number of chromosomes
* Used to produce seedless fruits
* To produce resistant species
* For the improvement of existing varieties of crops
* For producing new variety of crops
* It is used to identify the origin of natural alloploidy plants
* APPLICATION OF ALLOPLOIDY IN CROP IMPROVEMENT
* BRIDING CROSS
Because of the sterility in f1 the direct cross between two species is not possible therefore amphidiploids can be act as bridge
* PRODUCTION OF NEW CROP SPECIES
Alloploidy play important role in the creation of new crop species
EXAMPLE
* TRITICATE
* RAPHANOBRASSICA
* TRANSMISSION OF DESIRED GENE
Desired gene is transffered from the specific species
* SIZE
Sometimes plant breeder needs the plants with large size leaves and fruits for breeding purpose.
Plant size increases with increase in genome which increases with increase in nucleus which result in increase in size.
* HETEROSIS
Polyploidy enhances the heterosis (crossing two lines to produce superior progeny which result from the combination of genes male and female parents.) Which ensure the hetero-zygosity in future generation
* SELF FERTILIZATION
Polyplooidy is used to reduce the hurdles that prevent self fertilization.
It is also related to the asexual reproduction in plants.
