Download Cause and effect of mutation

Mutations and genetic
variation
Learning outcomes:
1. Causes of mutations
2. Effects of mutations
3. Type of mutations
Keywords
• Gametic mutation – permanent change to
DNA of gametes, inherited mutation
• Somatic mutation – permanent change to
DNA of normal body cells, affects
person during their lifetime but not
passed on.
• Gene mutations – Mutations that affect
one gene arise from point mutations – a
change in the nucleotides on a DNA
strand.
Keywords continued
• Chromosome mutation – occur during
meiosis and result in whole sections of
the chromosome being changed.
• Aneuploidy – having an extra or missing
chromosome due to non-disjunction
during meiosis.
• Polyploidy – having more than 2n
chromosomes in each cell, usually only
occurs in plants.
What causes mutations?
• http://www.youtube.com/watch?v=zcae
SKiZ37Y
• http://www.youtube.com/watch?v=JLrM
S_zs1kE
What causes mutation
• Mutations are spontaneous
• Increases in the number of mutations
are caused by environmental factors
(mutagens)
• UV light
• X-rays
• Benzene, formaldehyde, carbon
tetrachloride
Gametic and somatic mutations
• Gametic – testis of males, ovaries of
females, inherited
• Somatic – in normal body cells occuring
beyond zygote formation, not inherited
but may effect the person during their
lifetime. Chimaeras
Mutagens and their effects
• Ionising radiation –
Nuc radiation, xrays,
gamma rays (e.g.
medical treatment)
associated with
development of
cancers (e.g.
leukaemia, thyroid
cancer and skin
cancer)
Mutagens and their effects
• Viruses and
microorganisms –
integrate into
human chromosome,
upset genes and can
trigger cancer
Mutagens and their effects
• Environmental
poisons –
Organic
solvents such
as
formaldehyde,
tobacco, coal
tars, benzene,
asbestos, some
dyes
Mutagens and their effects
• Alcohol and diet –
High alcohol intake
increase the risk of
some cancers. Diet
high in fat and those
containing burned or
highly preserved
meat
The effect of mutations
• Not all are harmful
• For some it can be a survival advantage
• Most common among bacteria and
viruses but also seen in insects
• If no selective pressure against it, a
mutation may remain in gene pool.
Harmful mutations
• Cystic fibrosis and sickle cell anaemia
• Disfunctional proteins
• Albinism – caused by mutation in gene of
enzyme pathway of melanin
Beneficial mutations
• Bacteria – antibiotic
resistance through
mutation, transfer between
bacterial species
• Superbugs such as MRSA
have arisen this way
• RNA viruses – such as HIV
– mutates it’s protein coat
so that the host human is
unable to make antibodies
quick enough against it
Neutral mutations
• Neither harmful or beneficial to the
organism but may be important in an
evolutionary sense
• Silent mutations
• Virtually impossible to detect because
no observable effect
SOME MUTATION EXAMPLES
Normal red
blood cell
“Sickle” cell
BENEFIT
Most mutations are harmful.
Beneficial ones more common with short generation times.
Many may be silent – not observed – and may only be selected for or against
at a later date.
Neutral mutations make no change at all, due to Degeneracy
Example:
DNA
mRNA
Amino acids
Mutant DNA
mRNA
GENE MUTATIONS
Three types : substitution, deletion, insertion
Mutations that affect one gene arise from point mutations
– a change in the nucleotides on a DNA strand.
Normal DNA
Normal polypeptide
Mutant DNA
mRNA
e.g. Sickle cell anaemia
Mutated DNA creates a STOP codon which
prematurely ends synthesis of the polypeptide
chain
Insertion
Deletion
Causes a frame shift – it stuffs up
the whole rest of the sequence.
Mutation: Insertion of C
Original DNA
Normal polypeptide
Mutant DNA
mRNA
Amino acids
Large scale frame
shift results in a new
amino acid
sequence. The
resulting protein is
unlikely to have any
biological activity.
Page 144
CHROMOSOME MUTATIONS
These can only occur during meiosis.
a.k.a. Block mutations.
Deletion:
Inversion:
Examples:
Examples:
Cri-Du-Chat, Prader-Willi
On chromosome 2 – unviable offspring
Translocation:
Duplication:
A section of one chromosome is lost
to another one
A section of one chromosome is
lost to its Homologue
Chromosomes 9 and 22 – chronic
leukaemia
WHOLE CHROMOSOME MUTATIONS
Normal (Euploid) humans have
46
chromosomes (2 exact sets).
Aneuploidy is the term for having 1 or more missing or extra.
Monosomy = only one of a pair
Polysomy = more than 2 of a pair, e.g. Trisomy = 3 homologues.
This normally results from non-disjunction during meiosis.
Somatic cell
Some examples:
Trisomy chromosome 21
(Down’s)
Monosomy sex chromosome
(XO = Turner’s)
Gametes
Trisomy sex chromosome (XXY
= Klinefelters)
POLYPLOIDY
n = haploid (gametes)
2n = diploid (normal individual)
3n or more = polyploidy
Usually only in plants.
Allopolyploidy – from a cross between 2 species.
Hybrids, being a recombination of 2 lines, often show increased hybrid
vigour.
Autopolyploidy – from the same species.
Autopolyploidy
Allopolyploidy
Page 159-160, Look at 161/2