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Genetics Final Exam > Chapter 7 > Flashcards

Chapter 7 Flashcards

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Biology 101 flashcards
1
Q

Mutations?

A

Heritable changes in the base pair sequence of DNA

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2
Q

Forward Mutation

A

Changes in wild-type allele to a different allele (A+–>a)

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3
Q

Reverse Mutation (reversion)

A

Changes a mutant allele back to wild-type (a–>A+)

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4
Q

Substitution

A

Replacement of a base by another:
Transition: purine replaced by another purine
Transversion: Purine replaced by a pyridimine (vice versa)

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5
Q

Deletion

A

block of one more more base pairs lost from DNA

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6
Q

Insertion

A

Block of one or more base pairs added to DNA

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7
Q

Point Mutations

A

Affect one or a few base pairs, alternate one gene at a time.
Can include transitions, transversions, small deletions or insertions

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8
Q

Rates of Mutations

A

Different genes have different rates.
Rates higher in gamete producing eukatyotes (meiosis)

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9
Q

Human MutationRates

A

Rate = 1x10-8
Every child has approx 60 mutations - most do not affect phenotype
Higher rate in sperm (2^-4 x 10^-8) - more mitosis

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10
Q

Are Revertants more or less rare than Forward Mutations?

A

Revertants are MORE RARE than forward mutations

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11
Q

Luris-Delbruck Fluctuation Experiment

A

Bacterial resistance arises from mutations that occured before exposure to bactericide.
- allows survival of cells with pre-existing resistance
Mutations are random and heritable

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12
Q

Depurination

A

Natural process
Hydopusis of purine base
1000/hr in every cell

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13
Q

Deamination

A

Natural
Removal of amino group
C to U
normal C-G –> A-T after replication

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14
Q

Cosmic and X-rays

A

Natural
break sugar-phosphate backbone
UV- thymine diamers

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15
Q

Oxidative Damage

A

Natural
8-oxodG mispairs with A
G-C –> mutant Y-A after rep

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16
Q

How do Cells Decrease Replication Mistakes

A

Proofreading:
Portion of DNA polymerase called 3’-5’ exonuclease can recongnize and remove mismatches

17
Q

Tautomerization

A

Results in replication mistakes
-each base has 2 tautomers that can interconvert and cause incorrest base matching

18
Q

Trinucleotide Repeats

A

20 human disease genes have unstable trinucleotide repeats (huntingtons)
- children have an expanded number

19
Q

Trinucleotide Cause

A

Expansion and contraction occur by slipped mispairing

20
Q

Mutagens

A

Agents that raise frequency of mutations above spontaneous rate

21
Q

H.J. Muller Experiment

A

Used X-ray on male flies and was able to determine that it raised the mutation rate

22
Q

How Mutagens Alter DNA: Base Replacement

A

Replace a base - base analogs - chem structure almost identical to normal base

23
Q

How Mutagens Alter DNA: Hydroxylation

A

alter base structure and properties - adds an OH
C matches with A not G

24
Q

How Mutagens Alter DNA: Alkylation

A

Alters base structure and properties - alkylating agents add ethyl or methyl groups
G matches with T not C

25
Q

How Mutagens Alter DNA: Deamination

A

alter base structure and properties - deaminating agents remove amine groups

26
Q

How Mutagens Alter DNA: Insertion

A

Insert between bases - intercalators
proflavin can cause base insertion and deletions

27
Q

Somatic Mutations

A

In non-germ cells
not heritable
can affect to survival and lead to cancer

28
Q

Ames Test

A

Used to determine if chemicals are carcinogens by testing Histidine
Many HIS- —> HIS+ = bad

29
Q

Base Excision Repair

A
  1. DNA glycosylase removes altered N base
  2. Nearby nucleotides removed
  3. New DNA synthesized to fill gap
    important for removing U caused by deamination
30
Q

Nucleotide Excision Repair

A
  1. UvrA + UvrB complex scans for distortions to double helix (thymine diamers)
  2. UvrB + UvrC complex cuts around the damaged DNA
  3. DNA polymerase fills the gap
31
Q

Double Stand Break Repair

A

Homologous Recombination:
- similar to meiosis
Nonhomologous end-joining
- repair of double-strand breaks

32
Q

Bacteria: methyl-directed mismatch repair

A

Corrects mistakes in replication
-MutS and MutL bind to mismatched nucleotides
- MutH cuts unmethylated strand Opposite methylated
- gap made in new strand by DNA exonuclease
- gap filled by DNA polymerase using old strand template

33
Q

Error Prone DNA Repair Mechanisms

A

SOS system - Bactria
- used at rep forks that stalled because of unrepaired damage
- bad DNA polymerase used
- adds random nucleotides
Microhomology Mediated End-joining (MMEJ)
- similar to NHEJ but nucleotides are removed at double- stranded breaks –> small deletions

34
Q

Examples of Hereditary Human Diseases Due to Defects in DNA Repair

A
  • Xeroderma Pigmentosum
    -Hereditary colorectal cancer
  • Hereditary forms of Breast Cancer - BCRA1 + BCRA 2
35
Q

Why are Mutations Important

A

to respond to changes in the environment, would die out without mutations

Genetics Final Exam (11 decks)

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