Chapter 7: Chromosome Mutations
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Transcript of Chapter 7: Chromosome Mutations
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Chapter 7: Chromosome Mutations
*Chromosome mutations/aberrations
Variation in chromosome number:*aneuploidy*euploidy*polyploidy
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Nondisjunction
Homologous chromosomes: during
anaphase I
Sister chromatids: during anaphase II
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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
viabilityIn Plants:
Maize, tobacco, evening primrose, Jimson weed*Segmental deletions
*Cri-du-chat (46,5p-)
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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+
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Down syndrome, 47,21+
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Polyploidy
1) Addition of one or more sets of
chromosomes (replication)
2) Combination of chromosome sets from different species
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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
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AllopolyploidyPolyploidy
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Variations in Chromosome StructureDeletions
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Variations in Chromosome StructureDuplications
Due to unequal crossing over:
A B C D
A B C D
A B C DA B C D
A B C D
A B C D
A B C DA B C D
A B C D
A B C DAA
B C DB C D
Crossover:
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Evolution of hemoglobin genes
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Variations in Chromosome StructureInversions
*Paracentric*Pericentric
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Variations in Chromosome StructureTranslocation
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Variations in Chromosome StructureTranslocation – unbalanced gametes are produced