PRE LEC 3: GENE MUTATION Flashcards
- Alteration in DNA sequence that is rare in
the population - Typically affects phenotype
- base - pair change in any part of the DNA molecule
- are recessive and cause a loss-of-function
GENE MUTATION
refers to theprocess of altering a DNA sequence.
MUTATE
EFFECTS OF MUTATION
- genes’ product is reduced or absent
“loss-of-function”
EFFECTS OF MUTATION
- gene’s activity changes
- tend to be dominant and are also called “TOXIC”
“gain-of-function”
- the differences between organisms caused by alternates form of DNA
GENETIC VARIATION
SOURCES OF GENETIC VARIATION
- GENOTYPE
- alteration/change at the DNA or chromosome level.
MUTATION
SOURCES OF GENETIC VARIATION
- “many forms”
- alteration in DNA sequence that is common in the population
- Do not severely affect the phenotype
- Short tandem repeats (microsatellites):
POLYMORPHISM
: short repeating units (2-6 nucleotides), vary in number among individuals and is often used in DNA
profiling and paternity testing
Short tandem repeats (microsatellites)
- refers to phenotype; describes an allele.
- depends upon how the mutation affects the gene’s product or activity, and usually connotes an abnormal or unusual characteristic.
- may also be a rare variant that is nevertheless “normal,” such as red hair.
MUTANT
___________ mutation treats HIV infection
CCR5
o Occurs in the gametes during DNA
replication before meiosis
o All cells will have the mutation
- are transmitted to the next generation of individuals.
germline mutation
- occurs in ANY CELL IN THE BODY except germ cells
- happens during DNA replication before mitosis
- passed to the next generation of cells but NOT PASSED TO ALL CELLS
- has “somatic mosaicism”
somatic mutation
occur in cells that divide often, such as skin and
blood cells
Somatic mosaicism
CAUSES OF MUTATION
- Changes in the nucleotide sequence of gene with no known cause
- Generally assumed to be accidental
- Originates as an error in DNA replication, may be due to the lack of DNA repair
- also manifests as “gonadal mosaicism”
Spontaneous mutation
likelihood of a gene to undergo mutation in a single generation or in a single gamete
Spontaneous mutation rate
where mutations are more likely to occur,
where sequences are repetitive
▪REPETITIVE SEQUENCES: symmetrical:
may confuse replication enzymes
Mutational hotspots
CAUSES OF MUTATION
- Result from the influence of external factors (mutagens), such as exposure to CHEMICAL/RADIATION
- may be the result of either natural/artificial agents
Induced mutation
- agents of mutations
MUTAGENS
MUTAGENS
- Base analogs,
- alkylating agents,
- intercalating agents,
- adduct-forming agents (acetaldehyde
and heterocyclic amines) - UV LIGHT
- IONIZING RADIATION
- base pairing mutation
- Base analogs,
- alkylating agents,
- intercalating agents,
- adduct-forming agents (acetaldehyde
and heterocyclic amines)
CHEMICAL MUTAGENS
point mutation, most common mutagen
➢ UV light, sunlight, and ionizing radiation
Radiation mutagens
can be found inserted into our DNA
➢ Viruses and transposable elements
Biological mutagens
caused by environmental pollutants and
lifestyle factors
➢ Tobacco smoke and alcohol
Environmental mutagens
Common products containing mutagens
- Hair dye
- Smoked meats
- Certain flame retardants in children’s sleepwear
- Food additives
- Developed by DR. BRUCE ARMES in 1970s
- commonly used method that uses bacteria (Salmonella typhimurium) to test if the chemical can cause mutation in the DNA of the test organism
- Indication: produces a measurable increase in the number of colonies
Ames Test
Accidental exposure to mutagens:
- Workplace contact before danger is known
- Industrial accidents
- Medical treatments (chemotherapy and
radiation) - Exposure to weapons that emit radiation
- Natural disasters that damage RADIATION EMITTING EQUIPMENT
Natural exposure to mutagens:
- Natural environment sources of radiation (cosmic rays, sunlight, & radioactive substances)
- Medical X-rays and occupational radiation hazards (ionizing radiation)
- Job sites with increased radiation exposure (weapon facilities, research lab, health care facilities, nuclear power plants, & certain manufacturing plants)
Types of Mutations
* Change of one base pair to another in a
DNA molecule
a. Transition
b. Transversion
c. Missense
d. Nonsense
e. Silent
f. Splice-site
Point Mutations
Point Mutations
: purine replaces PURINE (A-G) and pyrimidine replaces pyrimidine (T-C)
a. Transition
b. Transversion
c. Missense
d. Nonsense
e. Silent
f. Splice-site
TRANSITION
POINT MUTATIONS
- purine replaces a PYRIMIDINE (A-T; C-G) or vice versa
a. Transition
b. Transversion
c. Missense
d. Nonsense
e. Silent
f. Splice-site
TRANSVERSION