Chromosomal Mutation

1
Chromosomal Mutation

• Some genetic diseases are brought about by
  structural changes in chromosomes

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
2
Chromosome Mutation

• Definition
• Abnormalities in chromosomal structure
  (chromosome aberration) changes in chromosome
  number (aneuploidy / euploidy)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
3

• Types of chromosome mutation
• Chromosome aberration
• Chromosomal number alteration
• Aneuploidy
• Euploidy (polyploidy)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
4
Structural change/chromosomes aberration

• Changes in the chromosomes structure, are most
  frequently formed during mitosis or meiosis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
5
Chromosome Aberration

• Rearrangement a certain segment _at_ parts of
  chromosome
• 4 types
• Translocation
• Deletion (segmental deletion)
• Inversion
• Duplication

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
6
Translocation involves a region of a chromosome
breaking off and rejoining either the other end
of the same chromosome or another non-homologous
chromosome
1
2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
7
Robertsonian translocation

• Robertsonian translocation involves breaks at the
  extremes ends of the short arms of two
  nonhomologous chromosomes (13, 14, 15, 21 and 22)
• Named after the American insect geneticist
  W.B.Robertson
• Also called whole-arm translocation or
  centric-fusion translocation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
8
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
9
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
11
Deletion (segmental deletion) the lost of 1
segment containing 1 or more genes
Losing middle section
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
12

• When the chromosome breaks at two places and lead
  to the loss of the middle segment
• The segment lost may contain one or more genes
• The remaining end of chromosome will join again
  and become shorten

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
13

• Genetic disease Cri du chat syndrome (usually
  mentally retarded and cries like a cat mewing)
• Loss of a small part of the short arm of
  chromosome 5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
14
Cri du chat Syndrome
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
15

• Cri du chat is a rare syndrome (1 in 50,000 live
  births) caused by a deletion on the short arm of
  chromosome 5.
• The name of this syndrome is French for "cry of
  the cat," referring to the distinctive cry of
  children with this disorder.
• The cry is caused by abnormal larynx development,
  which becomes normal within a few weeks of birth.
  
• Infants with cri du chat have low birth weight
  and may have respiratory problems.
• Some people with this disorder have a shortened
  lifespan, but most have a normal life expectancy.
• Where does the abnormal chromosome 5 come from?
  In 80 percent of the cases, the chromosome
  carrying the deletion comes from the father's
  sperm.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
16
Inversion a region of a chromosome breaks off
and rotates through 180 before rejoining the
chromosome
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
17
Duplication a region of a chromosome becomes
duplicated an additional set of genes exists
ABCDEFGHI FGHI
Additional set of genes
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
18

• When a single locus or a large piece of a
  chromosome is present more than once in the genome

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
19
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19