2. What Are Mutations?
Changes in the nucleotide sequence
of DNA
May occur in somatic cells (aren’t
passed to offspring)
May occur in gametes (eggs &
sperm) and be passed to offspring
3. Are Mutations Helpful or
Harmful?
Mutations happen regularly
Almost all mutations are neutral
Chemicals & UV radiation cause
mutations
Many mutations are repaired by
enzymes
4. What Causes Mutations?
There are two ways in which DNA can
become mutated:
Mutations can be inherited.
Parent to child
Mutations can be acquired.
Environmental damage
Mistakes when DNA is copied
5. Are Mutations Helpful or
Harmful?
Some type of skin cancers and
leukemia result from somatic
mutations
Some mutations may improve an
organism’s survival (beneficial)
Immunity to HIV
6. Chromosome Mutations
May Involve:
Changing the
structure of a
chromosome
The loss or gain of
part of a
chromosome
8. Gene Mutations
Change in the nucleotide
sequence of a gene
May only involve a single
nucleotide
May be due to copying errors,
chemicals, viruses, etc.
9. DNA (antisense strand)
mRNA
Polypeptide
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
The antisense strand is the DNA strand which acts as
the template for mRNA transcription
20. Background to Phenylketonuria
Phenylalanine and tyrosine
are two amino acids that
humans obtain from protein
in their diet. During normal
metabolism, excess
phenylalanine is acted upon
by an enzyme
(phenylalanine hydroxide).
20
21. Phenylketonuria: aka - PKU
PKU is a hereditary
disorder caused by a
genetic defect which
disrupts this metabolic
pathway.
An affected person lacks
the normal allele of the
gene required to make the
enzyme Phenylalanine
Hydroxide
21
22. Phenylketonuria: Continued
Owing to this inborn error in
metabolism, phenylalanine is
no longer converted to
tyrosine.
Instead it undergoes
alternative pathways which
produces toxins which affect
the metabolism of brain cells
and severely limit mental
development.
22
23. Screening for PKU –
Newborn babies are
screened for PKU, and
sufferers are put on a diet
containing minimum
phenylalanine.
As a result the worst
effects of PKU can be kept
to a minimum.
23
24. Albinism
Albinism results from a mutation
which prevents the formation of
enzyme 3 (Melanocyte Tyrosinase).
As a result albinos fail to synthesize
melanin.
24
25. Albinism – the symptoms
Due to the total lack of the pigment melanin Albino’s
have characteristic
Very pale skin which fails to tan.
White hair
The colour of the iris is usually blue/gray or light
brown with some people having a reddish or violet
hue reflected through the iris.
In some cases there is vision problems.
They must avoid ultraviolet radiation and may require to
ware tinted glasses to assist with photophobia.
25
27. Cystic Fibrosis
Mucus is a slimy substance
secreted by the inner lining of
the wind pipe and intestine.
Mucus is made of a glycoprotein
which makes it thick, slimy and
perfect for protection and
lubrication.
The genetic information for
coding this glycoprotein is on
chromosome 7.
27
28. Cystic fibrosis:
due to gene mutation
If the info on the gene for the glycoprotein
is altered.... Two outcomes.....
1. Homozygous for the mutant allele: Make
abnormally thick and sticky mucous leading
to lung congestion and blockage of the
pancreatic duct = CYSTIC FIBROSIS.
2. Heterozygous for the mutant allele: they carry
the mutant allele masked in their genotype
28
30. Mutagenic agents –
Increases mutation rate.
These include
A variety of chemicals act as mutagens. E.g.
Bromouracil, are structurally similar to DNA bases, and are
inserted in place of normal bases.
Ethidium bromide has a structure that allows it to wedge
within the DNA double helix
Peroxides and mustard gas, chemically modify DNA.
Exposure to high-energy radiation (bombardment by
alpha, beta, or gamma particles) or ultraviolet light can
have a similar effect.
30
31. Example of chemical mutations
Mrs Smith: Ch13: Mutations an
Chromosomal Abnormalities 31
