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Genetics > 4. Genetic variations > Flashcards

4. Genetic variations Flashcards

(52 cards)

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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

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A

DNA polymerase with proofreading ability

22
Q

Direct repair of DNA

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A

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

23
Q

Excision repair of DNA

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A

Template is needed, in eukaryotes

24
Q

What kind of repair mechanisms exists in mitochondria?

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A

None, only repair mechanisms for nuclear DNA

25
Nucleotide-excision repair is defective in
- Xeroderma pigmentosum | + Cockayne syndrome, Trichothiodystrophy
26
3 ways to repair single strand damage (SSD)
- Nucleotide-excision repair - Base-excision repair - Mismatch repair
27
Mismatch repair is defective in
Hereditary non-polyposis colon cancer
28
Repair of double strand breaks (DSB)
- Homologous recombination | - Non-homologous end-joining
29
Template in homologous recombination
- Sister chromatid (after S phase) - Homologous chromosome =safety
30
Template in non-homologous end-joining
No template, may result in loss of nucleotides = deleterious
31
Mutations might be somatic or generative. Difference between the two
- 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
Increased risk for nondisjunction with age, might lead to
Change of chromosome number
33
Increased risk for replication errors with age, might lead to
Point mutations
34
What happens to the association between homologous chrs. in oogenesis with age?
Association gradually weakens (cohesion molecules detach from sister chromatids) -> eventually chiasma also dissociates
35
6 places where mutations can happen in the gene
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
Splicing mutations
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
By function, mutations may be (5)
- Back mutation/reversion - Lethal mutations - Suppressor mutation - Gain-of-function mutations - Loss-of-function mutation
38
Haploinsufficiency is a special type of .... mutation
Loss-of-function
39
Size of mutations
- Large scale: Genome mutations (chr. nr. change) - Medium scale: Chr. mutations (chr. structure change) - Small scale: Not visible
40
Frameshift mutation
If number of nucleotide is not a multiple of three
41
In-frame mutation
If number of nucleotide is a multiple of three
42
Tandem repeats
- Satellite DNA - Minisatellite (10-60bp) - Microsatellite (2- some bp)
43
Interspersed repeats
SINEs (short interspersed elements | LINEs (long interspersed elements)
44
Trinucleotide repeats (micro satellite) can be found in what regions?
Both in coding and non-coding regions
45
Cause of 40% of Hemophilia A
Inversion mutation due to recombination between L1 repetitive sequences within and outside the F8 gene
46
Sickle cell anaemia is the result of what kind of mutation
Missense mutation
47
Point mutations
- Silent - Missense - Nonsense
48
Silent mutation
Change in nucleotide sequence that does not change the AA specified by the codon
49
Missense mutation
A single nucleotide change resulting in a codon that codes for a different amino acid
50
Nonsense mutation
Change in nucleotide sequence that results in an early stop codon
51
Duchenne muscular dystrophy cause
Frameshift mutation leading to non-functional dystrophin
52
Becker muscular dystrophy cause
In frame mutation leading to a partially functional dystrophin

Genetics (17 decks)

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