Post on 15-Jan-2016
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Types of Chromosome Mutations
Chromosome Mutations: Changes in Chromosome Structure
A B C D E F A C D E F
A B C D E F A B B C D E F
A B C D E F A E D C B F
A B C D E F
G H I J K
A B C D J K
G H I E F
Deletion/Deficiency
Duplication
Inversion
Translocation
Nonallelic Homologous Recombination (NAHR)
Origins of Chromosomal Rearrangements
Chromosome Mutations
A B C D E F A C D E F
A B C D E F A B B C D E F
A B C D E F A E D C B F
A B C D E F
G H I J K
A B C D J K
G H I E F
Deletion/Deficiency
Duplication
Inversion
Translocation
Deletions
Deletions can be terminal or interstitial.
An intragenic deletion inactivates a gene;multigenic deletions affect several genes.
Homozygous condition for chromosomal deletion is often lethal.
Chromosome deletion cannot revert.
Synapsis of a normal chromosome and a deletion chromosome produces a deletion loop during meiosis.
In heterozygous deletions, recombination frequencies between genes outside the deletion are lower than normal.
normal chromosome
deletion chromosome
a a
Recessive alleles covered by a deletion are unmasked and are expressed phenotypically. This effect is known as pseudodominance.
Deletions
Cancer cells often harbor chromosome mutations.
Cells of a tumor do not always show the same chromosome mutation.
Chromosome-specific deletions are associated with certain tumors.
Chromosome Mutations
A B C D E F A C D E F
A B C D E F A B B C D E F
A B C D E F A E D C B F
A B C D E F
G H I J K
A B C D J K
G H I E F
Deletion/Deficiency
Duplication
Inversion
Translocation
Duplications
Arrangement of a duplication can be in tandem or reverse order.
Several pairing possibilities exist in heterozygotes of a normal chromosome and a side-by-side duplication.
Heterozygous condition results in a loop structure during meiosis.
Duplications (and higher order duplications) can occur by unequal crossing-over after asymmetric synapsis of chromosomes.
Chromosome Mutations
A B C D E F A C D E F
A B C D E F A B B C D E F
A B C D E F A E D C B F
A B C D E F
G H I J K
A B C D J K
G H I E F
Deletion/Deficiency
Duplication
Inversion
Translocation
Inversions
A B C D E F G H
A B C D E F G H
A B F E D C G H
A B C D E G F H
pericentric inversion
paracentric inversion
A heterozygote for a normal chromosome and an inversion will form an inversion loop during meiosis.
The number of recombinant products is reduced in inversion heterozygotes by:
1) elimination of crossing over products within the inversion loop, and
2) inhibition of pairing between homologues in the region of the inversion.
Pairing in paracentric inversion heterozygotes and resulting meiotic products.
Anaphase bridge results in random breakage of chromosomal material.
2 of 4 meiotic products are not genetically balanced and will not produce viable gametes.
Pairing in pericentric inversion heterozygotes and resulting
meiotic products.
Possible effects of inversion at the molecular level
No disruption of any gene.
Chromosomal rearrangement is the only result.
Disruption of one gene by chromosomal breakage.
Disruption of two genes and fusion of those two genes.