508 Chapter 15 • Large-Scale Chromosomal Changes Polyploidy is an abnormal condition in which there is a larger than normal number of chromosome sets. Poly-ploids such as triploids (3 3 ) and tetraploids (4 3 ) are common among plants and are represented even among animals. Organisms with an odd number of chromosome sets are sterile because there is not a partner for each chromosome at meiosis. Unpaired chromosomes pass randomly to the poles of the cell during meiosis, leading to unbalanced sets of chromosomes in the resulting ga-metes. Such unbalanced gametes do not yield viable progeny. In polyploids with an even number of sets, each chromosome has a potential pairing partner and hence can produce balanced gametes and progeny. Poly-ploidy can result in an organism of larger dimensions; this discovery has permitted important advances in horticul-ture and in crop breeding. In plants, allopolyploids (polyploids formed by com-bining chromosome sets from different species) can be made by crossing two related species and then doubling the progeny chromosomes through the use of colchicine
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.