1. 12.4 Mutations
Kinds of Mutations
Significance of Mutations

2. Kinds of Mutations
Sometimes, cells make a mistake in copying their DNA, inserting an incorrect base or even skipping a base as the new strand is put together.
Mutations: changes in the genetic material.
Gene mutations: changes in a single gene.
Chromosomal mutations: changes in a whole chromosomes.

3. Gene Mutations
Point mutations: gene mutations involving changes in one or a few nucleotides; occur at a single point in the DNA
Substitutions: one base is changed to another; usually only affects one amino acid
Effects of insertions and deletions can be much more dramatic.
If a nucleotide is added or deleted, the bases are still read in groups of three, but now those groupings are shifted
Called frameshift mutations because they shift the reading frame of the DNA
This kind of mutation may change every amino acid after that point.
Can alter a protein so much that it is unable to perform its normal function.

4. Chromosomal Mutations
Involves changes in the number or structure of chromosomes.
These change the locations of genes on chromosomes.
Deletions: the loss of all or part of a chromosome.
Duplications: extra copies of parts of a chromosome.
Inversion: reverses the direction of parts of chromosomes.
Translocations: occurs when part of one chromosome breaks off and attaches to another.

5. Significance of Mutations
Most mutations are neutral meaning they have little or no effect on the expression of genes or the function of proteins.
Others have major effects on the expression of genes.
These mutations offer great variability among species some of which may be beneficial.
These mutations may cause some of the disorders we have previously discussed.
Polyploidy: condition in which an organism has extra sets of chromosomes.

6. Causes of Mutations
Mutations are generally cause by one of two factors.
Either the DNA fails to copy correctly
Environmental factors cause the DNA to mutate

7. Effects of Mutations No change in phenotype Small change in phenotype
Big change in phenotype