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Types of Chromosome Mutations

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Page 1: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

Types of Chromosome Mutations

Page 2: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

Mammalian X Chromosome Inactivation

Calico cats are usually females heterozygous for orange allele and black allele at an X-linked locus.

Male calico cats are very rare. Why is this the case?

Page 3: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

X Chromosome Inactivation

Most genes on the inactivated X chromosome are silenced (turned off, not expressed).

Genes on the inactivated X chromosome remain silenced in descendant cells.

Heritable alteration of this type is an example of epigenetic inheritance.

Chromosomal DNA sequence remains unchanged.

Page 4: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

Mammalian X Chromosome Inactivation

Inactivated X chromosome becomes highly condensed, Inactivated X chromosome becomes highly condensed, darkly staining structure called Barr body. darkly staining structure called Barr body. State of inactivation is transmitted down the cell lineage.State of inactivation is transmitted down the cell lineage.

Page 5: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

Types of Chromosome Mutations

Page 6: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

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

Page 7: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

Nonallelic Homologous Recombination (NAHR)

Origins of Chromosomal Rearrangements

Page 8: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

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

Page 9: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

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.

Page 10: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

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.

Page 11: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

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

Page 12: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

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.

Page 13: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

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

Page 14: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

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.

Page 15: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

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.

Page 16: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

Pairing in pericentric inversion heterozygotes and resulting

meiotic products.

Page 17: Types of Chromosome Mutations. Mammalian X Chromosome Inactivation Calico cats are usually females heterozygous for orange allele and black allele at

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.


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