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
This is the end of the preview. Sign up
access the rest of the document.