In diploid (2n) organisms, there are two major types of chromosomal aberrations that are the result of changes in chromosome number. These are polyploidy and aneuploidy. Polyploidy results when cells acquire one or more sets of chromosomes beyond the "normal" number of sets. For example, triploids (3n) contain one extra set of chromosomes, and would therefore be sterile, since they cannot produce balanced gametes by meiosis.
Aneuploids are the result of changes in the individual number of homologous chromosomes in a set. This usually results from nondisjunction during meiosis (Figure 6-3). The aneuploid condition that results in three copies of a given chromosome is known as trisomy (2n+1).
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