Human Genetics chapter11 Flashcards
0
Q
2 ways mutation occurs?
A
- Mutations that affect chromosomes
- Mutations that affect nucleotide sequence (single genes) occur spontaneously from errors in DNA replication or exposure to chemicals and radiation: can be detected by sudden appearance of dominant mutation in a single generation
1
Q
What is the source of all genetic variation in humans and all organisms?
A
Mutation
2
Q
Mutation rate
when can it be measured?
How often normally?
A
- The number of events that produce mutated alleles per locus per generation (frequency of heritable changes in DNA, rate of mutation detected and repaired, whether mutation results in recognizable phenotype)
- Can sometimes be measured if
- dominant and results from one gene
- is fully expressed and completely penetrant
- have clearly established paternity
- never the result of non genetic factors - Single mutation per every million genes
3
Q
Why do mutations have different mutation rates
A
- Size of gene (Larger genes are bigger targets for mutations)
- Nucleotide sequence (some genes contain short nucleotide repeats that predispose them to a higher mutation rate)
- Spontaneous changes, like radiation and chemicals (G/C pairs are more likely to mutate than A/T pairs) modify base pairs
4
Q
Neurofibromatosis
A
- Pigmentation spots and tumors of the skin
- 1 in 3000 births
- One of the highest mutation rates known
- Over 300,000 bp long (big gene)
- Autosomal dominant
5
Q
Huntington disease
A
- Very low mutation rate
- CAG repeats over 40 in HTT gene will develop Huntington’s disease
- Autosomal dominant
6
Q
Radiation
A
- The process by which electromagnetic energy travels through space or a medium such as air.
- 54% radon, 8% cosmetic, 8% terrestrial, 11% internal, 11% x-Ray, 3% consumer products (82% nature)
7
Q
Background radiation
A
Radiation in the environment that contributes to radiation exposure.
8
Q
Chemicals
A
- PCBs
- Benzopyrene - a carcinogen in cigarette smoke and charred meats (binds to DNA and impedes replication machinery)
- Base analogs are mutagenic chemical that resemble nucleotides, incorporated during DNA/RNA
9
Q
Base analogs
Example?
A
- Mutagenic chemicals that resemble nucleotides and are incorporated into DNA or RNA during synthesis
- Ex. 5-bromouracil mutates A/T pair to G/C pair
10
Q
Chemicals that bind to DNA
A
- Chemicals that resemble base pairs, intercalating agents, insert themselves into DNA and distort the double helix, producing Frameshift mutations
- Results in addition or deletion of single base pairs
11
Q
Chemical modification of bases
A
- Chemical mutagens can modify bases in DNA and alter their base pairing properties, spontaneous
- Nitrous acid (HNO2) causes G/C pairs to become A/T pairs
12
Q
Nucleotide substitutions
A
- Mutations that alter the sequence, but not the number of nucleotides in a gene
- Usually involve one or small number of bases
13
Q
Missense mutations
Give an example
A
- Single nucleotide substitution mutations that replace one amino acid for another in the protein
- Do not always affect protein function and often lack phenotypic consequence
- Sickle cell anemia (single nucleotide change in the 6th codon in the beta globin gene)
14
Q
Sense mutations
A
- Produce longer than normal proteins by changing a stop codon to one that codes for an amino acid (elongates proteins)
