Question

A classical example of Allopolyploidy is?
(a)Brassica
(b)Raphano-brassica
(c)Raphanus
(d)All the above

Answer 1

Hint: Artificial hybridization of radish and cabbage(both 2N = 18) produces a sterile first-generation hybrid with one diploid chromosome set from either parent. Tetraploidization eventually produces a stable, true-breeding hybrid.

Complete answer:
The number of sets of chromosomes in an organism is known as the ploidy number. Having two sets of chromosomes means you are diploid or 2n. There are other animals and a number of other species of plants that are polyploidy meaning that they have more than two sets of chromosomes.
There are times when organisms may contain two or more sets of chromosomes that are from different species. When this happens, we say this as allopolyploidy.
Raphano-brassica is a classical example of allopolyploids. This was pro­duced by a Russian Scientist Karpachenko. He crossed Raphanus lativus with Brassica oleracea and obtained an F1 hybrid which was completely sterile. The sterility was because of complete non-homology between the genomes of Raphanus and Brassica. But some plants of Raphanobrassica were fertile obviously because of the doubling of the chromosomes.

So, the correct answer is, “Raphano-brassica.”

Note: Synthesized Raphanobrassica plants proved, in general, highly sterile. Some aneuploids resulted from 4x R. sativus × 4x B. oleracea crosses but most progenies were euploid and showed almost regular chromosome association. A number of stunted, deformed plants were obtained from both 2x and 4x crosses. Vigour, fertility and aneuploidy appeared unconnected in the amphidiploid.
-An interesting intergeneric hybrid Raphanobrassica was produced by the Karpenchenko in 1928 by crossing radish and cabbage.