1. DNA MUTATIONS Diseases Types Mutagens
Mutations are any change in the genetic make up of an organism and can occur naturally or can be increased by mutagens.
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Diseases
Types
Mutagens

2. Error rate is 1 in 1,000,000 replications.
TYPES OF MUTATIONS
Mutations can be spontaneous or natural as a result of errors in DNA replication or gamete production.
Error rate is 1 in 1,000,000 replications.
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POINT
BLOCK
CHROMOSOMAL ABBERATIONS

3. Point mutations
Involves a change to one of the DNA bases that makes up a gene.
Also known as a MISSENSE mutation.
Consequence varies depending on type of change.
Change DNA
Change amino acid sequence
Change protein
Change organism
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Three types of point mutation
deletion
insertion
substitution

4. Base Substitution But… Also
Involves one base in the DNA being substituted by another.
This mutation only affects one codon in the gene.
But…
ATA
UAU
Tyr
mRNA
DNA
ATT
UAA
STOP
T A C T T C A A A C C G C G T
DNA
C is replaced by T in the DNA.
Known as NONSENSE mutation
Totally different protein made
Effect on organism can be dramatic
Also
AGA
UCU
Ser
mRNA
DNA
AGG
UCC
T A C T T C A A A T C G C G T
End result is a different amino acid in protein.
Generally minor effect on protein/organism.
Serine is still added
Known as a SILENT mutation

5. Dramatic effect on protein made. Known as frame shift mutations.
Base Insertion/Deletion
Involves one base either being inserted or removed from the DNA sequence.
Both these mutations affect all codons after the insertion or deletion.
The earlier the mutation occurs in the sequence the greater the effect.
T A C T T C A A A C C G C G T
DNA
Dramatic effect on protein made.
Known as frame shift mutations.
T A C T T C A A A A C C G C G
Trp
Arg
BASE INSERTION
INSERTION
T A C T T C A A C C G C G T A

6. Block mutations
Involves large scale changes in DNA segments on chromosome.
Only occur during meiosis, formation of gametes (sex cells).
Can affect the functioning of many genes
Severe effect on functioning and characteristics of organism.
Change DNA
Change amino acid sequence
Change protein
Change organism
Four types of block mutation
inversions
translocations
deletions
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duplications

7. Deletion
Section of chromosome is lost, anywhere from three bases to large segments.
The DNA breaks due to the effect of mutagens. A D B E C F H G
STEP 1
genes A D B E C F H G
segment is lost
STEP 2
break A D E F H G
DNA ligase rejoins chromosome
STEP 3

8. Translocation
Section of chromosome breaks and is joined to another chromosome.
Problem when gametes formed-some receive extra genes, some deficient.
STEP 1 A D B E C F H G 3 4 2 5 1
segment removed
STEP 2 3 4 2 5 1 D E F H G
break D E F H G
DNA ligase joins segment
STEP 3 3 4 2 5 1

9. Duplication
Segment of one chromosome is added to the homologous chromosome.
Problem when gametes formed-some have double the genes, some have no genes.
STEP 1 A D B E C F H G D E F H G A B C
STEP 2
segment removed
break D E F H G
STEP 3 A B C

10. Inversion Section of chromosome falls out and rotates through 180o.
DNA ligase rejoins section but the genes are in reverse order.
There is no loss of genetic information. A D B E C F H G
STEP 1 A D B E C F H G
STEP 2
segment rotates 180o
break
segment rejoins
STEP 3 A D B E C F H G

11. Chromosomal abberations
Loss or gain of entire chromosomes- called aneuploidy.
Main cause is non-disjunction of chromosomes during meiosis.
Gametes end up with extra chromosome(s) or fewer than 23 chromosomes.
2 x 23
Normal diploid (2N) human cell containing 2 sets of chromosomes.
<23, >23
Through meiosis haploid (N) gametes are produced, containing only one set of chromosomes. 23
Mainly occurs with sex chromosomes.
Turner syndrome
Normal female
Metafemale
Normal male
Jacob syndrome XO XX
XXX XY
XYY
Examples

12. Mutagens
Chemicals or radiation that increase the likelihood of a mutation occurring.
Rate of mutation induced by mutagen is proportional to the dose of mutagen.
Mutagens cause a decrease in the stability of the DNA molecule.
Thus DNA more susceptible to error during replication or meiosis.
Viruses & micro-organisms
Incorporate into genome
Trigger cancers
Ionising radiation
Nuclear
UV rays
X rays
Types
Alcohol & dietary factors
High fat, alcohol
Trigger cancers
Environmental poisons/irritants
Benzene, asbestos
Tobacco tar, formaldehyde

13. Diseases Down syndrome Sickle cell disease Cystic fibrosis
Click on a disease to find out more about how it is caused by a mutation.
Sickle cell disease
Down syndrome
Cystic fibrosis

14. Sickle cell disease
haemoglobin
Haemoglobin is made up of 4 polypeptide chains (2 alpha & 2 beta chains).
Gene for beta chain is found on chromosome 11 and consists of 438 bases.
A mutation occurs in the gene coding for the beta chain.
The mutation is a substitution where adenine replace thymine on the DNA template strand.
As a result the amino acid valine replaces glutamic acid.
This change the properties of the haemoglobin and results in distorted red blood cells.
HBB gene on chromosome 11
normal red blood cell
sickle cell
This single point mutation has a dramatic effect. Individuals have many health problems, eg weakness, jaundice, anaemia, heart & kidney defects, brain damage, skin lesions and inflamed spleen.

15. Cystic Fibrosis AAA TAA TAG AAA CCA CAA TAA TAG AAA CCA CAA
CFTR gene on chromosome 7
Inherited disorder and occurs when an individual has both copies of the faulty gene.
The gene (CFTR) is found on chromosome 7 and normally contains 1480 amino acids.
A mutation occurs whereby the 508th triplet (AAA) is deleted resulting in a mutated CFTR protein of 1479 amino acids.
The abnormal protein is unable to control chloride ion balance in cells.
The build up of chloride ions in cells results in severe effects.
Individuals have reduced life expectancy, high salt levels, blocked airways, pancreatic deficiencies and males are infertile.
Cystic fibrosis is relatively common and occurs 1 in every 2500 individuals.
triplet deleted
TAA TAG AAA CCA CAA
DNA
506th 507th 508th 509th 510th
TAA TAG AAA CCA CAA
DNA
506th 507th 508th 509th 510th
AAA
AUU AUC UUU GGU GGU
mRNA
AUU AUC GGU GGU
ile ile gly val
mRNA
amino acids
ile ile phe gly val
amino acids

16. Down Syndrome 24 23 Non-familial Familial
Arise from having 3 copies of chromosome 21
known as trisomy-21.
Down Syndrome
Individuals have characteristic facial features, are relatively short, slowed intellectual and physical development.
Two main types of Down syndrome-97% non-familial, 3% familial. 24 23
One of the parent’s sex cells contains two no. 21 chromosomes, due to non-disjunction during meiosis.
Non-familial
Familial
One of the parents has only 45 chromosomes. A translocation has occurred where one of no.15 and one of no. 21 have joined together. One of the sex cells contain 23 but one of the 23 is the 15/21 chromosome. 15 21
15/21
Parent 1
Parent 2
Down child 3 no.21