Natural Allopolyploidy in Brassica spp

1. Natural Allopolyploidy in Brassica sp.
Presented by-
Amrit Kumar Nayak
Adm.no- 41c/15
2nd Year Bsc.(Ag)

2. INTRODUCTION
• GENOME:-A genome is an organism’s complete set of DNA, including all of its
genes. Each genome contains all of the information needed to build and maintain
that organism.
• Polyploidy:-The condition in which a normally diploid cell or organism acquires
one or more additional sets of chromosomes. In other words, the polyploid cell
or organism has three or more times the haploid chromosome number.
Polyploidy arises as the result of total nondisjunction of chromosomes during
mitosis or meiosis.
•Origin of Polyploidy:- Different degrees of polyploidy are originated by different
means. However, 2 basic irregular process have been discovered by which
polyploids may evolve from diploid plants
• Somatic Doubling:- Cell sometimes undergo irregularities in mitosis and give
rise to meristematic cells that perpetuate these irregularities in new generations
of plant
• Reproductive process:- Irregular reductive division in which chromosomes fail
to separate completely.
• Induction of Polyploidy:- Polyploidy can be induced artificially by chemical
agents like colchicine or by physical means like X-Ray.

3. Types of Polyploidy
• Autopolyploids:- Autopolyploidy describes the multiple
occurrence of a set of chromosomes in a cell, a tissue or a whole
organism. An autopolyploid nucleus is a type of Polyploid
nucleus which, is formed when the single cell has diploid set of
chromosomes both from the same parent. This means that the
chromosomes are homologous rather than fusion from different
species during reproduction.
• Allopolyploids:- A polyploid containing genetically different
chromosome sets from two or more species is known as
Allopolyploid. Almost all natural allopolyploids have 2 copies of
each genomes.This has led to speciation or evolving of new
species from existing ones.

4. Origin of Allopolyploidy
• Natural allopolyploids most likely originated
through chromosome doubling of F₁ hybrid between
two distinct species.
• chromosome doubling may have occurred in
somatic cells of F₁ hybrids due to irregular mitosis.
•Alternatively,irregular meiosis may lead to the
production of unreduced gametes.
•Such gametes may unite to produce amphidiploid
progeny.
• Amphidiploid:- an interspecific hybrid having a
complete diploid chromosome set from each parent
form —called also allotetraploid.

5. Effects of Allopolyploidy
• Genetic Effects:- They generally have combined
morphological and physiological features of parent
species. In general allopolyploids are more vigorous
than diploids, but this isn’t true in all cases.
• Cytology:- They show variable frequencies of
multivalents. This produces variable sterility and leads
to both cytogenetic and genetic instability.
• Role in Evolution:- Allopolyploids have been more
successful as crop species than autopolyploids. Many
of our present day crops like wheat, cotton, tobacco
are allopolyploids. It has greatly contributed to
EVOLUTION of plants.

6. A.AUTOPOLYPLOIDY
B.Allopolyploidy

7. Natural Allopolyploidy in Brassica sp.
• Genome allopolyploidy is seen in Brassica sp.
•Genome allopolyploidy is the state where two or more distinct
genomes are brought together through hybridization between
two or more species followed by doubling of the resulting
hybrid.
• The F1 is often completely sterile because of irregular
chromosome distribution at Al due to lack of pairing between
the chromosomes of the different genomes.
• Chromosome doubling of the F1 hybrid produces an
allotetraploid which has two copies of each of the two parental
genomes; as a result bivalents are formed in the allotetraploid
due to pairing between homologous chromosomes
(autosyndesis or homo-genetic pairing) which makes it fertile.

8. NATURAL ALLOPOLYPLOIDY IN BRASSICA SP.
BRASSICA:
•The genus brassica belongs to the family cruciferae and consists of
both diploid and polyploid species. There are three elementary
species, namely, B. Nigra, (2n = 16; BB), B. Oleracea (2n = 18; CC)
and B. Campestris (2n = 20; AA).
•Chromosome pairing studies have revealed that these species of
brassica evolved from some ancestral species with “x = 6”, though
the process of Dysploidy.
• Dysploidy may be defined as the condition where basic
chromosome number differs within a population or species.
•The three elementary species gave rise to amphidiploids
(allotetraploids) through natural hybridization and subsequent
chromosome doubling.
•The allotetraploid species are Brassica carinata (2n = 34, BBCC), B.
juncea (2n = 36, AABB), and B. napus (2n; = 38, AACC).

9. Brassica Triangle

10. Infernces From Brassica Triangle
•The relationship among the different Brassica
speciesstarted to be explained by Morinaga (1934) and U
(1935) with the already-cited U-triangle, and accordingto
them, the diploid species B. rapa (AA-genome), B. nigra
(BB-genome), and B. oleracea (CC-genome) originated
along the same time as the allotretrapoid species B. juncea
(AABB), B. napus(AACC), andB. carinata (BBCC).
• It helps to determine the lineage of the species.
•The evolution of the species was identified by the
mitochondria and chloroplast genomes, which are co-
inherited and thereby could evidence for the more recent
origin of the allopolyploid species.
• It can help in improving environmental stress tolerance in
a species and can have more vigour than parent plant.

11. THANK YOU!!!
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