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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. - PowerPoint PPT Presentation
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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
In Plants:
Maize, tobacco, evening primrose, Jimson weed
*Segmental deletions
*Cri-du-chat (46,5p-)
Trisomy*Condition in which one chromosome is present in three copies (2n+1)
In Drosophila and humans:
Has severe effects, usually lethal
In Plants:
Jimson weed, rice
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
PolyploidyAutopolyploidy
The benefits of autopolyploid breeding:
increased size of plant organs- roots, leaves, flowers fruits, seeds
Arise in several ways:
*failure of all chromosomes to segregate during meiosis
*two sperm may fertilize an ovum
*experimentation
Allopolyploidy
Polyploidy
Variations in Chromosome StructureDeletions
Variations in Chromosome StructureDuplications
Due to unequal crossing over:
A B C D
A B C D
A B C D
A B C D
A B C D
A B C D
A B C D
A B C D
A B C D
A B C D
A
A
B C D
B C D
Crossover:
Evolution of hemoglobin genes
Variations in Chromosome StructureInversions
*Paracentric
*Pericentric
Variations in Chromosome StructureTranslocation
Variations in Chromosome StructureTranslocation – unbalanced gametes are produced