1. Mutations (Ch 13.3)

2. Types of Mutations Mutation: heritable changes in genetic information
Remember there is a checking system to stop mutations, but not all errors can be caught
Two Categories of Mutations
Gene mutations: produce changes in a single gene (plant height)
Chromosomal mutations: produce changes in whole chromosomes (multiple genes)

3. Gene Mutations
Point Mutations: gene mutations that involve changes in one or a few nucleotides because they occur at a single point in the DNA sequence
These mutations occur during replication
One cell is altered = all cells replicated from that cell is altered
Three types:
Substitutions
Insertions
Deletions

4. Gene Mutations Substitutions
One base is changed to a different base (substituted)
It only changes one amino acid normally
Sometimes it will change the amino acid and sometimes it will not (remember many different codons can code for a single amino acid)
Example:
CCC → CCA = proline to proline
CCC → ACC = proline to threonine

5. Gene Mutations Insertions / Deletions
One base is inserted or deleted from the DNA sequence
If a base is added or deleted it shifts the codon triplets and drastically affects the amino acids
Frameshift mutations: they shift the reading frame of the genetic message
They can alter the protein so much that it will not be able to perform its function
Insertion

6. Chromosomal Mutations
Chromosomal mutations: involve changes in the number or structure of chromosomes
Changes location of genes on chromosomes or the copies of some genes
Four Types:
Deletion: the loss of a chromosome
Duplication: an extra copy of part or all of the chromosome
Inversion: reverses the direction of parts of a chromosome
Translocation: part of one chromosome breaks off and attaches to another chromosome

7. Effects of Mutations
Mutations may or may not affect the organism depending on the type of mutation
Most mutations occur in DNA replication
Stressful environmental conditions could influence mutation rates (50% genes + 50% environment)
Mutagens: chemical or physical agents in the environment
Cells can sometimes repair the damages, but sometimes they remain permanent
Examples:
chemical = tobacco smoke / physical = X-rays

8. Beneficial Effects of Mutations
Mutations often produce proteins with new or altered functions that can be useful to organisms in a changing environment
Examples:
Insects resisting pesticides
Humans resist HIV
Humans increase bone strength
Plants chromosomes fail to separate during meiosis → triploid (3N) or tetraploid (4N) organisms (polyploidy) = larger and stronger

9. Harmful Effects of Mutations
Sickle Cell Disease
defective allele in hemoglobin the oxygen carrying protein in red blood cells
makes hemoglobin stick together when the oxygen levels decrease
Sickle cell shape gets stuck in the capillaries and damages cells, tissues, and organs
Cystic Fibrosis (CF)
Deletion of the amino acid phenylalanine
Need two copies of CF allele to affect the person (recessive)
CF causes digestive problems and produces thick mucus that clogs their breathing passageways

10. Harmful Effects of Mutations
Huntington’s Disease
Caused by a dominant allele for protein found in brain cells
CAG = glutamine = repeated over and over again
Effects
Mental deterioration
Uncontrollable movement
Greater the number of codons the earlier the disease appears and the more severe the symptoms