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Genetics > 4. Genetic variations > Flashcards

4. Genetic variations Flashcards

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Biology 101 flashcards
1
Q

Significance of genetic variability

A

Provides raw material for evolution and allows the adaptation of the species to unexpected changes of environment

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2
Q

Genetic variability is increased by (6)

A
  1. Sexual reproduction
  2. Meiosis (generation of gametes)
  3. Homologous recombination (crossing over)
  4. Independent assortment of homologous chromosomes
  5. Fertilisation
  6. Mutations (new variations produced)
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3
Q

Which allele is the most frequents in a population?

A

The normal/wild allelic variant

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4
Q

A mutant is an allelic variant of a DNA sequence which…

A

Causes disease (has recently occurred and it has reference)

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5
Q

Polymorphism

A

Is an allelic variant of a DNA sequence, which has no effect on phenotype and its frequency is >1% in a population

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6
Q

Spontaneous mutations can be caused by

A
  • Spontaneous chemical reactions in bases (tautomerization, deputisation, deamination)
  • Errors in DNA related processes (relocation, recombination, repair)
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7
Q

Frequent tautomer of adenine

A

Amino form

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8
Q

Rare tautomer of adenine

A

Imino form

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9
Q

Tautomerization of an adenine residue can result in..

A

Transition of A-T to a G-C base pair

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10
Q

Rare tautomer of cytosine and adenine

A

Imino form

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11
Q

Rare tautomer of thymine and guanine

A

Enol form

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12
Q

Process of depurination

A
  1. A base eg. G is lost (depurination)
  2. Apurinic site cannot provide a template for a complementary base on the newly synthesized strand
  3. Nucleotide with incorrect base (usually A) -> Into new strand
  4. Next round of replication. Wrong nucleotide used as template
  5. =Permanent mutation
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13
Q

Deamination

A

Removal of NH2 to produce different nucleotide

  • Cytosine -> Uracil (repaired)
  • Cytosine -> Thymine (not repaired)
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14
Q

Examples of induced mutation

A

By environmental agent =mutagen

  • Physical: Radiation (heat, UV, ionization)
  • Chemicals (natural toxins, synthetic substances)
  • Biological: Viruses
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15
Q

Checkpoints in cell cycle

A
  • Restriction point (right before S)
  • G2 (right before M)
  • M (spindle)
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16
Q

Participants of checkpoint machinery

A
  • Sensor and transducer (protein kinases)
  • Effector
  • Senses and stops cell cycle in case of DNA damage
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17
Q

Transducers of G1 checkpoint

A

ATM and BRCA1

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18
Q

Mutation of ATM causes

A

Ataxia telangiectasia

  • Neurodegenerative, inherited (AR) disease
  • Characterized by radio sensitivity and different tumors
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19
Q

BRCA mutation found in

A

Breast, ovarian and other types of cancer

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20
Q

Effector of G1 checkpoint

A

p53

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21
Q

Responsible for correction of DNA errors

A

DNA polymerase with proofreading ability

22
Q

Direct repair of DNA

A

The change is reversed, no template is needed, mainly in prokaryotes

23
Q

Excision repair of DNA

A

Template is needed, in eukaryotes

24
Q

What kind of repair mechanisms exists in mitochondria?

A

None, only repair mechanisms for nuclear DNA

25
Q

Nucleotide-excision repair is defective in

A
  • Xeroderma pigmentosum

+ Cockayne syndrome, Trichothiodystrophy

26
Q

3 ways to repair single strand damage (SSD)

A
  • Nucleotide-excision repair
  • Base-excision repair
  • Mismatch repair
27
Q

Mismatch repair is defective in

A

Hereditary non-polyposis colon cancer

28
Q

Repair of double strand breaks (DSB)

A
  • Homologous recombination

- Non-homologous end-joining

29
Q

Template in homologous recombination

A
  • Sister chromatid (after S phase)
  • Homologous chromosome
    =safety
30
Q

Template in non-homologous end-joining

A

No template, may result in loss of nucleotides = deleterious

31
Q

Mutations might be somatic or generative. Difference between the two

A
  • Somatic: Passed on to other somatic cells but not to next generation
  • Generative: In primordial germ line, inherited from one generation to the next one
32
Q

Increased risk for nondisjunction with age, might lead to

A

Change of chromosome number

33
Q

Increased risk for replication errors with age, might lead to

A

Point mutations

34
Q

What happens to the association between homologous chrs. in oogenesis with age?

A

Association gradually weakens (cohesion molecules detach from sister chromatids) -> eventually chiasma also dissociates

35
Q

6 places where mutations can happen in the gene

A
  1. Promotor region -> dec. transcription
  2. Exon -> AA change or truncated protein (stop)
  3. Intron -> Errors in splicing
  4. Polyadenylation site -> Dec. mRNA stability
  5. 5`UTR -> Dec. protein synthesis
  6. 3´UTR -> Disturbed translation and localisation
36
Q

Splicing mutations

A

When there is a mutant splice donor (or acceptor) e.g. donor GU is changes for CU. Next sequence is recognised as donor sequence -> mutant RNA

37
Q

By function, mutations may be (5)

A
  • Back mutation/reversion
  • Lethal mutations
  • Suppressor mutation
  • Gain-of-function mutations
  • Loss-of-function mutation
38
Q

Haploinsufficiency is a special type of …. mutation

A

Loss-of-function

39
Q

Size of mutations

A
  • Large scale: Genome mutations (chr. nr. change)
  • Medium scale: Chr. mutations (chr. structure change)
  • Small scale: Not visible
40
Q

Frameshift mutation

A

If number of nucleotide is not a multiple of three

41
Q

In-frame mutation

A

If number of nucleotide is a multiple of three

42
Q

Tandem repeats

A
  • Satellite DNA
  • Minisatellite (10-60bp)
  • Microsatellite (2- some bp)
43
Q

Interspersed repeats

A

SINEs (short interspersed elements

LINEs (long interspersed elements)

44
Q

Trinucleotide repeats (micro satellite) can be found in what regions?

A

Both in coding and non-coding regions

45
Q

Cause of 40% of Hemophilia A

A

Inversion mutation due to recombination between L1 repetitive sequences within and outside the F8 gene

46
Q

Sickle cell anaemia is the result of what kind of mutation

A

Missense mutation

47
Q

Point mutations

A
  • Silent
  • Missense
  • Nonsense
48
Q

Silent mutation

A

Change in nucleotide sequence that does not change the AA specified by the codon

49
Q

Missense mutation

A

A single nucleotide change resulting in a codon that codes for a different amino acid

50
Q

Nonsense mutation

A

Change in nucleotide sequence that results in an early stop codon

51
Q

Duchenne muscular dystrophy cause

A

Frameshift mutation leading to non-functional dystrophin

52
Q

Becker muscular dystrophy cause

A

In frame mutation leading to a partially functional dystrophin

Genetics (17 decks)

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