Chromosome Mutations
Definitions
A mutation is any change in the DNA.
A chromosome mutation is a change in the structure or
arrangement of the chromosomes
w Numerical Changes
{ Euploidy -- Excess or Defficiency in the
number of the entire chromomosomal
complement.
{ Aneuploidy -- Excess or Defficiency in a single
chromosome.
w Structural Changes
Numerical Chromosome Mutations
Euploid -- “True Number”
The cell(s) have the same number of copies of all the
chromosome.
1. Monoploid (Haploid if a gamete)
2. Diploid (Often is not considered a Euploid)
3. Triploid
4. Tetraploid
Euploidy
Chromosomes shown at metaphase
Normal
Diploid
Euploid
Monoploid
Triploid
Tetraploid
Euploidy is an excess or deficiency for the entire
complement of chromosomes.
Euploidy
Organisms
w Plants, amphibians, lower reptiles
w Some cells in other organisms (liver, midgut, etc.)
Root Causes
w Nondisjunction
w Autoreduplication
Euploidy
(continued)
Origins
w Autopolyploidy
{ Often involving individuals within the same
species.
{ Infertile. Propagation by cloning.
w Allopolyploidy
{ Often involving individuals from different
species.
{ Fertile.
Dosage Concerns
Examples
Numerical Chromosome Mutations
Aneuploidy
Excess or Defficiency in a single chromosome.
1. Monosomy
2. Disomy (only if normally cell is not diploid)
3. Trisomy
4. Tetrasomy
Aneuploidy
Chromosomes shown at metaphase
Normal
Diploid
Aneuploid
Monosomic
Trisomic
Tetrasomic
Aneuploidy is an excess or deficiency for fewer than the
entire complement of chromosomes.
Aneuploidy
Organisms
w All organisms
w Variability in how they deal with it
Root Causes
w Nondisjunction
w Results of Chromosome Structure Mutations
Aneuploidy -- Examples
Plants
w Jimson Weed (Datura stramonium)
Animals
w Drosophila: Triploid females are viable & fertile.
Trisomy flies are not!
w Human (autosomal):
{ Trisomy 13 (Patau Syndrome) 1:20,000
{ Trisomy 18 (Edwards Syndrome) 1:10,000
{ Trisomy 21 (Down Syndrome) 1:700
{ Other rare ones (7, 9, 12, 14, & 22)
Aneuploidy Examples
w Human Sex Determining Chromosomes
1. Monosomy
{ 45,X (Turner Syndrome) 1:2000 female births
2. Trisomy
{ 47,XXX (Triplo-X) 1:1200 female births
{ 47,XYY 1:1000 male births
{ 47,XXY (Klinefelter Syndrome) 1:800 male
births
3. Tetrasomy & above
{ Klinefelter Syndrome 48,XXXY & 49,XXXXY
{ 48,XXXX & 49,XXXXX