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16 - Changes in Chromosome Number and Structure

Published online by Cambridge University Press:  05 June 2012

James N. Thompson, Jr
Affiliation:
University of Oklahoma
Jenna J. Hellack
Affiliation:
University of Oklahoma
Gerald Braver
Affiliation:
University of Oklahoma
David S. Durica
Affiliation:
University of Oklahoma
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Summary

STUDY HINTS

Errors in mitosis and meiosis can lead to aneuploid cells, that is, to cells that have more or fewer chromosomes than the normal diploid (the euploid, or literally “true multiple”) set of chromosomes. Because so many genes are involved in this change in the genetic makeup of a cell, most aneuploids die or are very abnormal. Among those that do survive, however, the addition of a chromosome is apparently more readily tolerated than is the loss of a chromosome.

A related type of genomic change is polyploidy, in which fusion of meiotic products, multiple fertilization, or defects in spindle formation result in extra complete sets of chromosomes (3n, 4n, and so forth). Although polyploidy can occur in either animals or plants, it is much more common in plants. Indeed it is an important evolutionary mechanism in plants that can yield new species. It is also a valuable tool of plant breeders who want to combine characteristics from separate but related species for agricultural purposes. Seedless polyploids are also economically useful.

It is useful to distinguish two types of polyploidy. Autopolyploidy (auto- means “self”) occurs when an inhibition of normal meiosis or other processes increases the number of chromosome sets within a single species. For example, species A (where 2n = AA) becomes an autotriploid (3n = AAA), autotetraploid (4n = AAAA), or higher multiple. Allopolyploidy (allo- means “different”), on the other hand, combines chromosome sets from different species.

Type
Chapter
Information
Primer of Genetic Analysis
A Problems Approach
, pp. 142 - 155
Publisher: Cambridge University Press
Print publication year: 2007

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