6.2 Mutations
Pages 234-239

Mutations can be caused by:
- environmental agents
- errors during cell division

Radiation
Exposure to radioactive materials can cause genetic mutations.

Chemicals
• Examples: Nitrosonguanidine (NTG),
Hydroxylamine, Bromodeoxyuridine (BrdU), and Ethidium bromide

Effects
• Positive, negative or neutral effect on phenotype or cell death

Point Mutations
• A failure of the genetic machinery to copy the
DNA perfectly.

Base-pair substitution
The wrong nitrogenous base pair is included.

Insertion
Extra nitrogenous bases are included during the copying of the DNA.

Deletions
• One or more base pairs are left out during the copying of DNA

Chromosome mutations
Involve the entire chromosome or major chunks
Non-disjunction (sister chromatids fail to separate during meiosis)
• Down syndrome
• Turner syndrome
• Patau syndrome

Chromosome mutations
• Large scale deletions, insertions, duplications or inversions (flipping) of entire portions of a chromosome

Inheriting mutations
• The genetic machinery is designed to find and fix copying errors. (less successful with age)

Inheriting mutations
• Most of the DNA does not code for genes (so errors here are meaningless)

Inheriting mutations
• Mutations in autosomes are not passed on to the next generation

Inheriting mutations
• Mutations in sex cells can be passed on to the next generation

Dominant vs. Recessive
• Mutations can be dominant and appear in the first generation. Ex. Huntington’s disease
• Mutations can be recessive and appear only rarely when two individuals with the same mutation produce offspring. Ex. Cystic Fibrosis

Sickle cell anemia
• Misshapen red blood cells can cause pain and an increased risk of infection

Sickle cell anemia
• Malaria parasite enters red blood cell causing it to become sickle-shaped and leading to its destruction and removal.

Lactose Tolerance
• Most babies tolerate lactose producing the enzyme needed to digest their mother’s milk
• 75% of adults do not tolerate lactose
• 25% of adults have a mutation in their genes that allows them to digest lactose.

Spontaneous mutations
• Happen by accident

Induced mutations
• Result due to exposure to a physical or chemical agent

Antibiotic Resistance
• Usually antibiotics kill bacteria by weakening their cell wall.
• Mutations in genes that code for the cell wall allow the bacteria to be resistant to antibiotics.

Jumping Genes
• Transposons are segments of the DNA that can move from place to place.
• Transposition is the act of moving a segment of DNA from one place to another.
• Example: Indian corn

hemophilia
• A transposon can insert itself into a gene for normal blood factor VIII, causing hemophilia in boys (X-linked gene).

Microarray Technology
Microarray
-small membrane or glass slide
-contains samples of hundreds or even thousands of DNA fragments
-arranged in a regular pattern.
-Each fragment corresponds to a gene

Microarray