chapter 7: chromosome mutations
DESCRIPTION
Chapter 7: 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 PresentationTRANSCRIPT
Chapter 7: 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
viabilityIn 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
AllopolyploidyPolyploidy
Variations in Chromosome StructureDeletions
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:
Evolution of hemoglobin genes
Variations in Chromosome StructureInversions
*Paracentric*Pericentric
Variations in Chromosome StructureTranslocation
Variations in Chromosome StructureTranslocation – unbalanced gametes are produced