1. Mutations

2. Mutations
These are any permanent, random changes in the DNA or genetic make-up of a cell.
Remember, DNA codes for the formation of proteins, and proteins are the structure of the body as well as the enzymes that catalyse every chemical reaction in the body.
If a mutation occurs it can cause everything from a mild effect to a lethal one.

3. Mutations
In Nature there is always a certain mutation rate, which can be increased by certain environmental factors.
In humans, the normal spontaneous mutation rate for a single gene is 1 mutation in every 106 to 108 replications.
Since humans have about genes, this means that the normal mutation rate is about 1 gene per person per generation.

4. Mutations
Most of these mutations are recessive, and so are hidden.

5. Effects of Mutations Most mutations are bad for the organism.
Many, though not lethal, produce organisms that are less fertile, as viable or as effective as the normal.
If a mutation occurs in a body cell, the result is more likely to be a form of cancer or cell death – these are not passed on to the next generation.

6. Mutations in Body Cells

7. Effects of Mutations
Mutations that occur in the germ or reproductive cells are passed on to the next generation, and the offspring are called Mutants.

9. Mutagens These are agents that can cause a gene to mutate.
There are a number of mutagens.

10. High-Energy Radiation
E.g. cosmic rays, X-rays, UV radiation, radioactive decay.
Ionising radiation sometimes induces simple substitutions of bases in the DNA. It can also cause deletion of large chunks of genetic material.

11. High-Energy Radiation
UV light most often causes abnormal bonding between thymine bases.
When UV light is absorbed by 2 adjacent thymine bases, they bond together to form a Thymine Dimer, which if it goes unrepaired inactivates the DNA strand.

12. Chemicals
E.g. Mustard Gas, epoxides, nitrous acid, acridine dyes, alkylating agents and formaldehyde.
These chemicals react with specific nucleotide bases in the DNA and change their nature, possibly leading to mistakes in the pairing of nucleotides during replications.

13. Chemicals Nitrous acid is a powerful mutagen found in cigarette smoke.
It can change cytosine to uracil, and other bases to chemicals similar but not the same as adenine and guanine – so it can lead to errors in replication.
Most mutations can be repaired efficiently as long as your repair system is working well.

15. How Mutations Affect Organisms
Changing Biochemical Pathways
Take a biochemical pathway
A B C D

16. How Mutations Affect Organisms
Each step is catalysed by an enzyme. A B C D E1 E2 E3

17. How Mutations Affect Organisms
Each of these enzymes is coded for by a strip of DNA, or a gene. A B C D E1 E2 E3 G1 G2 G3

18. How Mutations Affect Organisms
A mutation in any gene 1, 2 or 3 could cause real problems to the completion of this chemical pathway.

19. How Mutations Affect Organisms
Changes to the Bases in Proteins
A mutation can cause a nucleotide base change on the DNA, in different ways:
It could cause a substitution where one base is changed for another.
Or an insertion where a base is added.
Or a deletion where a base is removed.
No matter what the change it will effect the protein formed.

20. How Mutations Affect Organisms
Changes to the Chromosome
A mutation may cause a whole chromosome to break up, or join onto the other chromosomes, or twist around.
Or it may cause a small piece to repeat itself over and over again.
This repeat piece often determines the severity of a disease.

21. Fragile X
This is a disease where there are repeat pieces of the X chromosome.
If there are only a few repeats, the effect is a learning difficulty but the person is able to function quite well.
If there are many repeat pieces, the person’s development is severely retarded.

23. How Mutations Affect Organisms
Changes in Cell Division
A mutation may upset cell division, and cause whole chromosomes to move in the wrong direction or not separate properly.
This results in people with more than 2 of a chromosome, or organisms with double or more sets of chromosomes.

24. Good or Bad
Remember not all mutations are bad.