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Presentation on Evolution of Raphanobrassica

1. Evolution Of Crop Species Presented By- Paritosh Mishra Adm No-46C/15 2nd Yr. B.Sc.(Ag.) 2. Polyploidy I. Types of polyploidy A. Autopolyploidy: more than 2…
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  • 1. Evolution Of Crop Species Presented By- Paritosh Mishra Adm No-46C/15 2nd Yr. B.Sc.(Ag.)
  • 2. Polyploidy I. Types of polyploidy A. Autopolyploidy: more than 2 genetically identical genomes B. Allopolyploidy: combines the genomes of more than one species C. Intermediate situations, e.g. segmental allopolyploids D. Ancient polyploidy followed by chromosomal repatterning and restoration of diploid-like chromosome behavior "diploidization"
  • 3. Allopolyploids There are times when organisms may contain two or more sets of chromosomes that are from different species. When this occurs, we refer to this as allopolyploidy. It may help to remember this if you think about the prefix, 'allo-,' meaning 'other' or 'different,' and that 'poly-' means 'many.‘
  • 4. Origin of Allopolyploids • Natural allopolyploids most likely originate through chromosome doubling of F1 hybrid produced by chance through natural hybridization between two distinct species of the same genus or from different genera. • Experimental production of allopolyploids is achieved through chromosome doubling of F1 hybrid with the help of colchicine. • Such allopolyploids are often called synthetic allopolyploids. The synthesis of allopolyploids involves two steps. i. Production of F1 hybrids by crossing two distinct species and ii. Chromosome doubling of such F 1 hybrids. The man made cereal Triticale is an example of synthetic allopolyploid.
  • 5. Amphidiploid …double diploid, 2n1 + 2n2 …have balanced gametes of the type n1 + n2, these gametes fuse to make fertile 2n1 + 2n2.
  • 6. Origin of Raphanobrassica  An allotetraploid has been produced by the Russian Geneticist G.D. Karpechenko (1927) by crossing Raphanus sativus (2n = 18) and Brassica oleracea (2n = 18).  The hybrid formed by crossing these two species is itself a diploid (2n = 18). It contains only one set of radish chromosome (n = 9) and one set of cabbage (n = 9) chromosomes.  The hybrid differs from both the parents and showed many characters of both.
  • 7. Genetics Of Raphanobrassica  It is almost sterile, because radish and cabbage chromosome are so different that they do not pair or fail to pair at meiosis I. But the hybrid forms an occasional gamete which contains one complete set of radish chromosomes and one complete set of cabbage chromosomes.  When such two gametes combine they produce a plant which contains two sets of radish chromosome and two sets of cabbage chromosomes (18+18 = 36). These F2 progenies were fertile and tetraploids. At meiosis, pairing was regular and the plant was fertile. This plant showed foliage like radish and root like cabbage. The fruit was peculier.
  • 8. Hybridisation
  • 9. Rabbage Cross
  • 10. Morphology Of Raphanobrassica  It resembled the cabbage in its lower portion and the radish in its apical portion.  The allotetraploid bred true, hence of no practical value.  As it combines characters of both radish and cabbage, therefore, has been named Raphanobrassica.
  • 11. Fig: Raphanobrassica
  • 12. Raphanobrassica: A Profit from Loss  However, the experiment was significant and it demonstrated a method by which fertile interspecific hybrids can be obtained.  Attempts to produce a fertile hybrid between potato and tomato, with underground parts like potato and aerial parts like tomato, have also been unsuccessful so far.  Some of the synthetic allotetraploids resemble closely with the existing species.  Various species like wheat, cotton, tobacco etc. might have developed by this method. During the recent years a new genus Triticale has been synthesised by combining the chromosome of Triticum duram and Secale cereale (rye).  This new genus Triticale is a very useful allopolyploid (2n = 56).
  • 13. Thank you
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