Chapter 8: Chromosome Mutations
*Chromosome mutations/aberrations
Variation in chromosome number:
*aneuploidy
*euploidy
*polyploidy
Nondisjunction
Homologous chromosomes:
during anaphase I
Sister chromatids:
during anaphase II
Monosomy
*Condition in which one member of a chromosome pair is missing (2n-1)
In Drosophila:
Haplo-IV are monosomic for chromosome 4
develop more slowly, reduced size, impaired viability
*develop
In Plants:
Maize, tobacco, evening primrose, Jimson weed
*Segmental deletions
*Cri-du-chat (46,5p-)
1
Trisomy
*Condition in which one chromosome is present in three copies (2n+1)
In Plants:
Jimson weed, rice
In Drosophila and humans:
Has severe effects, usually lethal
Exceptions:
Patau syndrome, 47, 13+
Edwards syndrome, 47, 18+
Down syndrome, 47, 21+
Polyploidy
1) Addition of one or more
sets of chromosomes
(replication)
2) Combination of
chromosome sets from
different species
2
Autopolyploidy
Arise in several ways:
*failure of all chromosomes to segregate during meiosis
*two sperm may fertilize an ovum
*experimentation
The benefits of autopolyploid breeding:
increased size of plant organs- roots, leaves, flowers fruits, seeds
Allopolyploidy
Variations in
Chromosome Structure
Deletions
3
Variations in Chromosome Structure
Duplications
Crossover:
A
A
A
A
B
B
B
B
C
C
C
C
D
D
D
D
A
A
A
A
B
B
B
B
C
C
C
C
D
D
D
D
A
A
A
A
B
B
B
B
C
C
C
C
D
D
D
D
Due to unequal crossing over:
Evolution of hemoglobin genes
Variations in Chromosome Structure
Inversions
*Paracentric
*Pericentric
4
Variations in
Chromosome
Structure
Translocation
Variations in
Chromosome
Structure
5