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Principles of Disease > Mutations and Genetic Analysis > Flashcards

Mutations and Genetic Analysis Flashcards

1
Q

Incidence of chromosomal abnormalities

A

First-trimester miscarriages = 50%
Children with mental retardation = 35-40%
Congenital malformations = 5-10%

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2
Q

trisomy accounts for

A

50% first trimester miscarriages

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3
Q

main trisomy include

A

other trisomy
trisomy 16
trisomy 21

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4
Q

monosomy accounts for

A

20% first trimester miscarriages

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5
Q

trisomy 21 is

A

downs syndrome

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6
Q

Monosomy 45 X means

A

only 45 chromosomes, one X being missing (this is Turner syndrome).

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7
Q

in liveborn infants most common is the abnormality

A

trisomy 21

45 X

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8
Q

Trisomy 47,XX +13 causes

A

Patau

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9
Q

Trisomy 47,XY +18 causes

A

Edwards

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10
Q

Trisomy 47,XX +21

A

downs syndrome

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11
Q

47,XXY causes

A

Klinefelter

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12
Q

in trisomy 13, 18, 21 and and 47XXY, origin of disjunction is usually from

A

maternal side

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13
Q

in monosomy 45X, origin of disjunction is usually from

A

paternal side

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14
Q

Unbalanced Robertsonian translocation (4%) is linked to

A

downs syndrome

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15
Q

Autosomal aneuploidy syndromes:

downs syndrome

A 
Incidence: 1 in 650 to 1 in 700
Characteristic facial dysmorphologies
IQ less than 50
Average life expectancy (50-60 years)
Alzheimer’s disease in later life
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16
Q 
Autosomal aneuploidy syndromes:
Trisomy 13 (Patau syndrome)
A

Incidence: 1 in 5000
Multiple dysmorphic features and mental retardation
About 5% die within first month, very few survive beyond first year

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17
Q

Unbalanced Robertsonian translocation (10%) is linked to

A

Trisomy 13 (Patau syndrome)

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18
Q 
Autosomal aneuploidy syndromes:
Trisomy 18 (Edwards syndrome)
A

Incidence: 1 in 3000

Severe developmental problems; most patients die within first year, many within first month

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19
Q

Sex chromosomes aneuploidy syndromes:

45,X (Turner syndrome)

A

Incidence: 1 in 5000 to 1 in 10000 (liveborn)
Females of short stature and infertile
Neck webbing and widely spaced nipples
Intelligence and lifespan is normal

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20
Q

Sex chromosomes aneuploidy syndromes:

47,XXY (Klinefelter syndrome)

A

Incidence: 1 in 1000
Tall stature, long limbs
Male but infertile, small testes, about 50% gynaecomastia
Mild learning difficulties

21
Q

Structural abnormalities

A 
Balanced or unbalanced rearrangements
Translocations
Deletions
Insertions
Inversions
22
Q

Reciprocal Translocations:

A

involving breaks in two chromosomes with formation of two new derivative chromosomes

23
Q

Robertsonian Translocations:

A

fusion of two acrocentric (near end of one) chromosomes

no genetic information is lost: other translocations occur but do not lead to a viable fetus.

24
Q

deletion mutation is when

A

breaks in a chromosome leads to part of genetic material being deleted.
- unbalanced rearrangement

25
Q

inversion mutation types

A

pericentric
- breaks in chromosome involving centromere gets inverted

paracentric
- break in chromosome where part of chromosome gets inverted

both are balanced rearrangements

26
Q

genetic mutations can be

A 
Germline or somatic
Gene disruption /disease-associated
Polymorphism
- No phenotypic effect
- Frequency >1%
27
Q

Types of mutations

A

Non-coding

Coding

28
Q

Coding mutations

A

Silent – synonymous e.g. CGA (Arg) to CGC (Arg)
Missense e.g. CGA (Arg) to GGA (Gly)
Nonsense e.g. CGA (Arg) to TGA (Stop)
Frameshift – deletion / insertion e.g. CGA (Arg) to CCGA (Pro, then out-of-frame

29
Q

mutations detection methods

A

Polymerase chain reaction (PCR) - In vitro technique

Gel electrophoresis
Restriction fragment length polymorphism (RFLP) analysis
Amplification refractory mutation system (ARMS)
DNA sequencing

30
Q

What do we need for PCR?

A 
Sequence information
Oligonucleotide primers
DNA
Nucleotides
DNA polymerase
31
Q

in PCR denaturation occurs at

A

93-95 degrees C

32
Q

in PCR annealing occurs at

A

50-70 degrees C

33
Q

in PCR extend occurs at

A

70-75 degrees C

34
Q

Gel electrophoresis

A 
Separate DNA fragments by size
Apply an electric field - direction of migration is from negative to positive
DNA is negatively charged
Separate through agarose gel matrix
Visualise DNA fragments
35
Q

Advantages of Gel electrophoresis

A

Speed
Ease of use
Sensitive
Robust

36
Q

PCR applications

A 
DNA cloning
DNA sequencing
In vitro mutagenesis
Gene identification
Gene expression studies
Forensic medicine
Typing genetic markers
Detection of mutations
37
Q

ARMS (Amplification Refractory Mutation System) and primers

A

normal primer causes amplification

mutant primer causes no amplification

38
Q

ARMS (Amplification Refractory Mutation System)

Advantages

A

Cheap
Labelling not required
Electrophoresis required
Primer design critical

39
Q

ARMS (Amplification Refractory Mutation System)

Disadvantages

A

Need sequence information

Limited amplification size

40
Q

Restriction endonucleases are

A

Enzymes from bacterial cells

  • Protective mechanism
  • Degrade DNA of invading viruses
  • Recognise specific DNA sequences
  • Usually 4-8 bp
  • Always cut DNA at the same site
41
Q

RFLP analysis is

A

PCR and digest

42
Q

RFLP Advantages

A

Simple
Cheap
Non-radioactive

43
Q

RFLP Disadvantages

A

Requires gel electrophoresis

Not always feasible

44
Q

DNA sequencing:

Sanger

A

Chain termination method

45
Q

ddNTP has

A

h groups

46
Q

dNTP has

A

OH group

47
Q

DNA sequencing:

Advantages

A

Gold standard for mutation detection
Automation and high throughput
Next generation sequencing
- 18 billion bp in 4 days (about 6 human genomes)

48
Q

DNA sequencing:

Limitations

A

Expensive equipment
Poor quality sequence read
- First part of sequence (15 to 40 bases)
- Deterioration after 700-900 bases

49
Q

Choice of method

A 
Direct test
Quick and easy
Cheap
Sensitivity
Specificity

Principles of Disease (27 decks)

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