AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

ALLOPOLYPLOIDY

• Allopolyploids are polyploids resulted from the multiplication of chromosome sets of closely related species; however, the different chromosome sets are only partly homologous ( homeologous ), not fully homologous, as they are in autopolyploids.
• The allopolyploidy does not occur naturally in the nature.
• However, some cytologists have produce allopolyploidy in certain plants by selective breeding methods.
• The Russian cytologist, G. D. Karpechenko ( 1928 ) first synthesized an allotetraploid genus called Rhaphanobrassica from the artificial crosses between vegetables belonging to different genera, the radish ( Raphanus satirum, 20 = 18 ) and the cabbage ( Brassica oleracea, 2n= 18 ) in an attempt to produce a hybrid plant with edible portions of the root and the shoot of cabbage.
• However, this hybrid was functionally sterile because the 9 chromosomes from the cabbage parent were different from the radish chromosomes such that pairs did not synapse and segregate normally.
• Fertile amphidiploid arose from spontaneous doubling in the 2n=18 sterile hybrid.
• This kind of allopolyploid is sometimes called an amphidiploid , which means doubled diploid.
• Allopolyploids can be used in plant breeding to combine the useful features of parental species into one type.