*(REVISE) FOR LAST POST
Analogy of frame-shift mutation
one sentences
CAN YOU BUY CAT FOR HER SON
after insertion only one alphabet , A at CAT in the sentence,
CAN YOU BUY ACA TFO RHE RSO N
we can't read that sentence
after delete only one word, C at CAT in the sentence
CAN YOU BUY ATF ORH ERS ON
we can't read that sentence
*peringatan analogi ini untuk kefahaman sahaja ianya tidak boleh digunakan dalam peperiksaan
7.3: CHROMOSOMAL MUTATION
• Definition: Abnormalities ~ in chromosomal structure (chromosome aberration) & changes in
chromosome number (aneuploidy / euploidy)
• Chromosomal mutations take place when the number of chromosomes changes or when structural
changes occur in the chromosomes
• Classification chromosomal mutation
i) Chromosomal aberration (structural of chromosomal change)
ii) Chromosomal number alteration
- Aneuploidy
- Euploidy (polyploidy)
Chromosomes aberration
• Changes in the chromosomes structure, are most frequently formed during mitosis or meiosis
• Rearrangement a certain segment @ parts of chromosome
• 4 types of chromosomal aberration
i) Translocation
ii) Deletion (segmental deletion)
iii) Inversion
iv) Duplication
Translocation
Translocation : involves a region of a chromosome breaking off and rejoining either the other end of the same
chromosome or another non-homologous chromosome
• e.g. 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
Deletion
Deletion : the lost of 1 segment containing 1 or more genes
• 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
• 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
• 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.
Inversion
Inversion : a region of a chromosome breaks off and rotates through 180° before rejoining the
chromosome
Duplication
Duplication : a region of a chromosome becomes duplicated; an additional set of genes exists
• Whena single locus or a large piece of a chromosome is present more than once in the genome
Alteration of chromosomes number
• Type of the alteration of chromosomal number
i. aneuploidy
ii. euploidy / polyploidy
• Human somatic cells containing a number of chromosomes which is not a multiple of 23 are called
aneuploids
Aneuploidy
• Aneuploidy is a condition in which the number of chromosomes is abnormal due to extra or missing
chromosomes, in other words, it is a chromosomal state where the number of chromosomes is not a
multiple of the haploid set.
• Normal diploid species have 2n chromosomes, where n is the number in the haploid set.
• Aneuploid individuals would have 2n-1 chromosomes (monosomy), 2n+1 chromosomes (trisomy), or
some other such arrangement.
• A change in the number of chromosomes can lead to a chromosomal disorder. Aneuploidy is common in
cancerous cells.
• Aneuploidy occurs during cell division when the chromosomes do not separate properly between the two
cells
Disjunction: chromosomes separated to the opposite poles during meiosis
Non disjunction : failure of pair of chromosome to separate and to move to the opposite poles
both sets of chromosomes pass to the same pole of the cell
Cause of aneuploidy
Nondisjunction in Anaphase I & II
Nondisjunction in Anaphase I and II (meiosis)
• Half the daughter cells produced have an extra chromosomes (n+1) whilst the other half have a
chromosome missing (n-1)
• Fusion gametes between chromosome (n+1) and normal gamete (n), produced embryo with
chromosome (2n+1) : Trisomy; eg. Down’s syndrome
• Fusion gametes between chromosome (n-1) and normal gamete (n), produced embryo with
chromosome (2n-1) : Monosomy; eg. Turner Syndrome
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