|Figure 6-2 Structural aberrations of chromosomes.
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
|Figure 6-3 Aneuploid gamete formation by nondisjunction
during (a) meiosis I and (b) meiosis II.
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).