1. Mutations and genetic variation
Learning outcomes:
Causes of mutations
Effects of mutations
Type of mutations

2. 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.

3. 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.

4. What causes mutations? http://www.youtube.com/watch?v=zcaeSKiZ37Y

5. 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

6. 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
Chimaeras – mixtures of cell types, some with the mutation and some without. May trigger the onset of cancer if the normal controls of gene regulation are disrupted

7. 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)

8. Mutagens and their effects
Viruses and microorganisms – integrate into human chromosome, upset genes and can trigger cancer
Aspergillus fungus release toxins that induce liver cancer

9. Mutagens and their effects
Environmental poisons – Organic solvents such as formaldehyde, tobacco, coal tars, benzene, asbestos, some dyes

10. 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
These pass through the gut slowly and allow buildup of irritants/mutagens in the bowel
Test knowledge: In your own words, explain where a mutation must occur to be inherited and give a brief reason why. Explain why inherited mutations are important in an evolutionary sense.

12. 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.
Survival – most common among viruses and bacteria – MRSA, also occur in multicellular organisms
Sometimes neutral and no immediate effect. If no selective pressure against it, a mutation may be carried in the population and be of benefit (or harm) at a future time

13. Harmful mutations Cystic fibrosis and sickle cell anaemia
Disfunctional proteins
Albinism – caused by mutation in gene of enzyme pathway of melanin
CF – loss of 3 nucleotides
Sickle cell anaemia – 1 base change
Albinism – not common in the wild because of predation

14. 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

15. 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
Double page 140 – 141 complete as homework

16. SOME MUTATION EXAMPLES
Normal red blood cell
“Sickle” cell

17. 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

18. 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
Mutated DNA creates a STOP codon which prematurely ends synthesis of the polypeptide chain
e.g. Sickle cell anaemia

19. Mutation: Insertion of C
Deletion
Causes a frame shift – it stuffs up the whole rest of the sequence.
Mutation: Insertion of C
Original DNA
Normal polypeptide
Large scale frame shift results in a new amino acid sequence. The resulting protein is unlikely to have any biological activity.
Mutant DNA
mRNA
Amino acids
Page 144

20. CHROMOSOME MUTATIONS These can only occur during meiosis.
a.k.a. Block mutations.
Inversion:
Deletion:
Examples:
Cri-Du-Chat, Prader-Willi
Examples:
On chromosome 2 – unviable offspring

21. Translocation:
A section of one chromosome is lost to another one
Duplication:
A section of one chromosome is lost to its Homologue
Chromosomes 9 and 22 – chronic leukaemia

22. WHOLE CHROMOSOME MUTATIONS
Normal (Euploid) humans have 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. 46
Somatic cell
Some examples:
Trisomy chromosome 21 (Down’s)
Monosomy sex chromosome (XO = Turner’s)
Trisomy sex chromosome (XXY = Klinefelters)
Gametes

23. 2n = diploid (normal individual)
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.

24. Autopolyploidy Allopolyploidy
Page , Look at 161/2