Download Mutations - Kaikoura High School

Mutations
• Any change in DNA sequence which is not
immediately and properly repaired.
• If they occur in somatic cells then they are
non-inheritable, if in gametes then can be
passed on to offspring.
• Can be due to mistakes in DNA replication
(spontaneous) or caused by mutagenic
agents e.g. UV light, ionising radiation,
Xrays, chemicals, viruses
• May be harmful, beneficial or neutral.
• Usually recessive in diploids, can pass
through many generations with no further
change.
• Two main types: gene mutations (point)
and chromosome mutations (block,
number of chromosomes or sets of
chromosomes)
Point Mutations
• These are single gene mutations. There is
a change in the DNA sequence of one
base. This affects the amino acid coded
for and therefore the protein. There are 3
types of point mutation.
• Substitution: a base is swapped for
another base, the code for the amino acid
may be changed resulting in a nonfunctioning protein. E.g. sickle cell
anaemia.
• Insertion: an extra base is added resulting
in a frame shift in the reading of the code
making a new sequence of amino acids.
• Deletion: a base is removed resulting in a
frame shift in the reading of the code
making a new sequence of amino acids.
E.g. cystic fibrosis.
• Tautomerism is where the wrong base
pairing occurs which results in the amino
acid sequence being misread.
Block mutations
• A change in structure of the chromosome.
Groups of genes are affected and often
occurs during crossing over or due to
mutagens. Four types:
• Deletion: loss of a section of chromosome
• Inversion: part of a chromosome turned
around.
• Translocation: part of one chromosome
breaks off and is joined to another
chromosome.
• Duplication: part of a chromosome is
copied and added to the chromosome.
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A bird bird flys thru the trees
Chromosome numbers
• Aneuploidy: loss or gain of whole
chromosomes
• Polyploidy: loss or gain of sets of
chromosomes.
• All cause diseases with multiple effects
which are called syndromes.
Aneuploidy
• Normally a human has pairs of
homologous chromosomes (disomy).
• Aneuploidy is where one pair of
chromosomes either has monosomy (only
1 chromosome) or trisomy (three
chromosomes).
• Can occur in autosomes (nonsex
chromosomes) e.g. downs, patau, edward
syndrome
• Can occur in sex chromosomes e.g.
Klinefelter (XXY) or Turner (XO)
syndrome.
Polyploidy
• 3+ complete sets of chromosomes,
common in plants and rare in humans
(spontaneously aborts).
• Autopolyploidy – within a single species
• Allopolyploidy – within hybrid