5.2 Mutations

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Types of Mutations

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

Radiation

Exposure to radioactive materials can cause genetic mutations.

Chemicals

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

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

Non-disjunction:• 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

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