1. Section 20.4 Mutations and Genetic Variation
Chapter 20
Section 20.4
Mutations and Genetic Variation

2. Mutations Mutations are changes in the sequence of a DNA molecule.
Mutations provide a source of new genetic variation to a population.
Mutations can be:
Beneficial – help an organism survive.
Neutral – does not affect survival.
Harmful – hinder an organisms survival.

3. 2 Main Types of Mutations
Point Mutation - a mutation that alters only one base pair.
Gene Mutation - a mutation that changes the coding for amino acids.

4. Point Mutation

5. Gene Mutation

6. Other Mutations
The following mutations can be classified as point or gene mutations based on the specific changes they make to the DNA sequence.
Silent Mutation
Missense Mutation
Nonsense Mutation
Frameshift Mutation
Deletion
Insertion
Translocation
Inversion

7. Silent Mutation
A mutation that does not result in a change in the amino acid coded for.

8. Missense Mutation
A mutation that results in the single substitution of one amino acid in the polypeptide.

9. Nonsense Mutation
A mutation that converts a codon for an amino acid into a stop codon.

10. Frameshift Mutation
A mutation that causes the reading frame of codons to change.
Can either be caused by the insertion or deletion of nucleotides.

11. Deletion
The elimination of a base pair or group of base pairs from a DNA sequence.

12. Insertion
The placement of an extra nucleotide(s) in a DNA sequence.

13. Translocation
The transfer of DNA from one site in the genome to another location.

14. Inversion
The reversal of a segment of DNA.

15. Causes of Genetic Mutation
Genetic mutations can either be spontaneous or induced.
Spontaneous mutations – occur as a result of errors made during DNA replication.
Induced mutations – are caused by a foreign chemical agent or radiation.
Substances that induce mutations are known as mutagenic agents.
Examples: UV radiation, cosmic rays, X-rays, tobacco, viruses, alcohol, STI’s, etc.

16. Inferring Relationships from DNA Sequences
Unit C: Cell Division, Genetics and Molecular Biology
Inferring Relationships from DNA Sequences
Phylogeny – the proposed evolutionary history of a species or group.
The phylogeny of a species can be determined based on the sequences of DNA.
More closely related organisms will have more similar DNA.