Chapter 8
Variation in Chromosome Structure and Number
Study Outline
I. Variation in Chromosome Structure
A. Natural variation exists in chromosome structure
B. Changes in chromosome structure include deletions, duplications, inversions, and
translocations
C. The loss of genetic material in a deletion tends to be detrimental to an organism
D. Duplications tend to be less harmful than deletions
E. Duplications provide additional material for gene evolution, sometimes leading to the
formation of gene families
F. Copy number variation is relatively common among members of the same species
G. Comparative genomic hybridization is used to detect chromosome deletions and
duplications
H. Inversions often occur without phenotypic consequences
I. Inversion heterozygotes may produce abnormal chromosomes due to crossing over
J. Translocations involve exchanges between different chromosomes
K. Individuals with reciprocal translocations may produce abnormal gametes due to the
segregation of chromosomes
II. Variation in Chromosome Number
A. Aneuploidy causes an imbalance in gene expression that is often detrimental to the
phenotype of the individual
B. Aneuploidy in humans causes abnormal phenotypes
C. Variations in euploidy occur naturally in a few animal species
D. Variations in euploidy can occur in certain tissues within an animal
E. Variations in euploidy are common in plants
III. Natural And Experimental Ways To Produce Variations In Chromosome Number
A. Meiotic nondisjunction can produce aneuploidy or polyploidy
B. Mitotic nondisjunction or chromosome loss can produce a patch of tissue with an altered
chromosome number
C. Changes in euploidy can occur by autopolyploidy, alloploidy, and allopolyploidy
D. Allodiploids are often sterile, but allotetraploids are more likely to be fertile
E. Experimental treatments can promote polyploidy
F. Cell fusion techniques can be used to make hybrid plants
G. Monoploids produced in agricultural and genetic research can be used to make
homozygous and hybrid strains