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MRCPsych > Molecular genetics > Flashcards

Molecular genetics Flashcards

1
Q

How many barr bodies in trisomy X?

A

2

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2
Q

What is a Barr body?

A

When X chromosome is inactivated

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3
Q

How does X inactivation occur?

A

DNA methylation

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4
Q

What is mutation in SHANK3 associated with?

A

Autism

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5
Q

Mutation in KISS1 gene

A

Kallmann syndrome - hypogonadotrophic hypogonadism

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6
Q

What is the heritability of bipolar?

A

75-85%

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7
Q

What are the purines?

A

Adenine and guanine

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8
Q

What are the pyrimidines?

A

Thymine and cytosine

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9
Q

What are the possible base pairs of DNA?

A

TA
AT
GC
CG

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10
Q

What does genetic abnormality of Progranulin cause?

A

Frontotemporal dementia

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11
Q

Where is progranulin gene found?

A

17q21

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12
Q

What is locus heterogeneity?

A

Same disease phenotype caused by mutations at different loci

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13
Q

What is a cloning vector?

A

Small piece of DNA into which foreign DNA fragment can be inserted

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14
Q

What is polymorphism?

A

Natural variations in a gene, DNA sequence or chromosome that have no adverse impact on the individual & occur with fairly high frequency in the general population

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15
Q

Which gene encodes for serotonin transporter?

A

SL6CA4

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16
Q

Where is SL6CA4 found?

A

Chromosome 17 - 17q11

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17
Q

Where would you find COMT?

A

22q11

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18
Q

How is fragile X inherited?

A

X-linked

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19
Q

Which trinucleotide repeat is responsible for Fragile X?

A

CGG

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20
Q

What is heritibility?

A

Proportion of variation of an observed feature that is due to genetic factors

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21
Q

What are the 3 steps of PCR?

A
  1. DS DNA denatured by heat into single strand then annealed by cooling
  2. DNA polymerase used to extend primers in opposite directions. After 1 cycle there are 2 copies of DNA, after 2 cycles there are 4 copies.
  3. Cycling is set to produce the necessary number of amplifications
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22
Q

What is the lifetime risk of unipolar depression in a first degree family member with bipolar disorder?

A

10-20% (2-3x greater than general population)

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23
Q

What % of the human genome is considered to be active with coding sequences?

A

2%

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24
Q

Where is mitochondrial DNA inherited from?

A

Ovum

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25
Q

How many autosomes in a human cell?

A

44

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26
Q

What is the law of segregation?

A

For any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent to an offspring

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27
Q

Which nuclear component undergoes splicing?

A

Intron

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28
Q

What is an intron?

A

Any nucleotide sequence within a gene that is removed by RNA splicing to generate final mature RNA product of gene

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29
Q

Gene associated with late onset dementia

A

APO E on chromosome 19

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30
Q

What is an inframe mutation?

A

Changes happening in multiple of 3 bases with no disturbances to the actual reading frame

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31
Q

What is epistasis?

A

Gene-gene interaction between different alleles of different genes

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32
Q

What is alternate splicing?

A

Where one gene gives rise to more than one protein

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33
Q

LOD score for statistical evidence of linkage

A

Over 3

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34
Q

LOD score evidence something not linked

A

-2 or less

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35
Q

Maternal inheritance of Huntington’s effect on disease severity

A

More severe disease

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36
Q

3 stop codons

A

UAA
UGA
UAG

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37
Q

Southern blot test

A

Visualises restriction fragment length polymorphisms

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38
Q

How are genetic distances expressed?

A

centiMorgans

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39
Q

What is one centiMorgan equivalent to?

A

1% recombination frequency between two loci

1,000,000 base pairs of DNA

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40
Q

Difference between missense and nonsense mutation

A

Missense - new mutant codon specifies a different amino acid with variable effects on final protein product
Nonsense - new codon codes for stop code

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41
Q

Which cells remain in G0 stage indefinitely?

A

Liver cells

Neurons

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42
Q

How is Noonan’s inherited?

A

Autosomal dominant

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43
Q

What is a Robertsonian translocation?

A

Where chromosomes break at their centromeres and the 2 long arms fuse to form a metacentric chromosome
Non-reciprocal translocation involving 2 homologous pairs or non-homologous chromosomes

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44
Q

Which enzyme mediates the binding of tRNA with amino acids?

A

Aminoacyl synthetase

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45
Q

Risk of AD in patient who is heterozygous for APOE4 compared to those with no APOE4 allele

A

3x higher

For homozygous 15x

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46
Q

How is Rett’s inherited?

A

X-linked dominant

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47
Q

Best technique to detect large sequence of DNA

A

South blotting

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48
Q

Role of RNA polymerase

A

Synthesis of RNA from a DNA template

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49
Q

Features of Argyll-Roberston Pupil

A

Will accommodate but light reflex absent

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50
Q

Deletion of which chromosome causes Prader-Willi?

A

Paternal 15q11 q13

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51
Q

What method can be used to detect abnormal trinucleotide repeats?

A

PCR

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52
Q

What phenomena explains most epigenetic variations?

A

DNA methylation and histone modifications

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53
Q

Which form of inheritance might skip a generation and then reappear?

A

Autosomal recessive

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54
Q

Which gene is mutated in PKU?

A

Phenylalanine hydroxylase

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55
Q

How are monozygotic twins formed?

A

When an embryo is cleaved during early development

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56
Q

How are dizygotic twins formed?

A

Fertilisation of 2 different ova by 2 different sperm

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57
Q

What % of genes do dizygotic twins share?

A

50%

58
Q

What is the lifetime risk of developing schizophrenia in a sibling of a patient?

A

10%

59
Q

CADASIL is associated in a mutation in which gene?

A

NOTCH3

60
Q

What is CADASIL?

A

Cerebral Autosomal Dominant Ateriopathy with Subcortical Infarcts and Leukoencephalopathy

61
Q

What is transcription?

A

Using DNA template to form RNA

62
Q

What is replication?

A

Forming DNA from DNA

63
Q

What is translation?

A

Using RNA template to form protein

64
Q

What are the polypeptide coding sequences in DNA called?

A

Exons

65
Q

What are non-coding sequences in DNA?

A

Introns

66
Q

What are the 3 types of sequences introns contain?

A

Satellite - large sequence of repeats
Minisatellite
Microsatellite - single, di or tri nucleotide repeats

67
Q

What happens to all introns in mRNA before starting protein synthesis?

A

They are removed

68
Q

Where does translation take place?

A

Cytoplasm aided by ribosomes

69
Q

3 steps of translation

A
  1. Initiation
  2. Elongation
  3. Termination
70
Q

Gene problem Smith-Magenis

A

17q11.2

71
Q

Features of Smith Magenis syndrome

A

Self hugging
Pulling off nails
Inserting foreign objects into orifies

72
Q

Williams gene problem

A

17q11 microdeletion

73
Q

Cri-du-chat syndrome gene

A

Deletion of chromosome 5p

74
Q

What is incomplete penetrance?

A

Patients have dominant disorder but it does not manifest itself clinically

75
Q

How might a female manifest a X-linked recessive disorder?

A

Unfavourable lyonization - deactivation of most normal alleles

76
Q

How is tuberous sclerosis inherited?

A

Autosomal dominant

77
Q

Gene and features of TS

A

9q34

Adenoma sebaceum, cysts, brain hamartomas

78
Q

Treacher collins features

A

Autosomal dominant
Maxilla-mandibular hypoplasia
Down slanting palpebrae
Mild to moderate MR

79
Q

Treacher collin gene

A

5q31

80
Q

Apert syndrome gene

A

10q

81
Q

Apert syndrome features

A 
Autosomal dominant
Craniosynostosis 
Shallow orbits 
Trapezoid mouth 
Mitten hands
82
Q

Noonan syndrome gene

A

Chr 12

83
Q

Noonan syndrome features

A

Mild MR
Short stature
Webbed neck
Pulmonary stenosis

84
Q

How is Hurler syndrome inherited?

A

Autosomal recessive

85
Q

Hurler syndrome gene

A

4p16

86
Q

Hurler syndrome features

A

Deteriorating IQ after 2 years
Coarse facies
Clouded cornea
Joint stiffness

87
Q

Lesh-Nyhan gene

A

Xq26-27

88
Q

How is Lesch-Nyhan inherited?

A

Autosomal recessive

89
Q

Best known example of X-linked dominant disease

A

Vitamin-D resistant rickets

90
Q

Fragile X trinucleotide repeat

A

CGG - proximal to FMR1 gene

91
Q

Friedreich Ataxia trinucleotide repeat

A

gAA

92
Q

Huntington chorea trinucleotide repeat

A

CAG

93
Q

Myotonic dystrophy trinucleotide repeat

A

CTG

94
Q

Southern blotting

A

Detection of specific sequence in DNA

95
Q

Western blotting

A

Detection of specific protein after electrophoresis

96
Q

Northern blotting

A

Detection of specific RNA sequence after electrophoresis

97
Q

What is FISH used for?

A

Localise specific DNA sequences on a chromosome

98
Q

Heritability estimate Schizophrenia

A

80

99
Q

Heritability estimate BPD

A

Over 80

100
Q

Heritability estimate major depression

A

40

101
Q

Heritability estimate anxiety

A

30

102
Q

Heratibility estimate panic

A

40

103
Q

Heratibility estimate alcoholism

A

60

104
Q

Big 5 personality traits and their heratibility

A 
Openness - 57% 
Extraversion - 54%
Conscientiousness - 49%
Neuroticism - 48%
Agreeableness - 42%
105
Q

What is Hardy-Weinberg equilibrium?

A

In the absence of mutation, non-random mating, selection and genetic drift, the genetic constitution of the population remains the same from one generation to the next

106
Q

What is alllelic heterogeneity?

A

Same disease phenotype from different mutations at same loci (e.g. CF - 600 mutations at chromosome 7 resulting in same disease)

107
Q

What is pleiotropy?

A

Single disease causing mutation affects multiple organ systems e.g. Marfan’s

108
Q

MZ vs DZ concordance of male alcoholism

A

41% vs 22%

109
Q

MZ vs DZ concordance of Bulimia

A

23% vs 9%

110
Q

MZ vs DZ concordance Autism

A

64% vs 9%

111
Q

Tourette’s MV vs DV concordance

A

53% vs 8%

112
Q

Female alcoholism MZ vs DZ concordance

A

34% vs 31%

113
Q

Genes implicated in Schizophrenia (6)

A 
DISC1
COMT 
NRG1 (neuregulin)
DTNBP1 (dysbindin)
DAAO
RGS4
114
Q

Where is DISC1 gene

A

1q42

115
Q

Most frequent personality disorder in relatives of patients with Schizophrenia?

A

Schizotypal

116
Q

General population risk of schizophrenia

A

1%

117
Q

First cousins risk of Schizophrenia

A

2%

118
Q

Uncles/Aunts risk of Schizophrenia

A

2%

119
Q

Nephews/Nieces risk of Schizophrenia

A

4%

120
Q

Grandchildren risk of Schizophrenia

A

5%

121
Q

Half siblings risk of Schizophrenia

A

6%

122
Q

Parents risk of Schizophrenia

A

6%

123
Q

Siblings risk of Schizophrenia

A

9%

124
Q

Children risk of Schizophrenia

A

13%

125
Q

Identical twins risk of Schizophrenia

A

48%

126
Q

Fraternal twins risk of schizophrenia

A

17%

127
Q

Risk of BAD in population, 1st degree rel & monozygotic twins

A

pop - 0.5-1.5%
1st - 5-10%
mono - 40-70%

128
Q

Lifetime risk of unipolar disorder in general pop, 1st degree rel and monozygotic twin

A

pop - 5-10%
1st - 10-20%
Mono - 15-25%

129
Q

Which genes are suspected in BAD?

A

COMT
BDNF
DAO G72/G30

130
Q

Genes in early onset dementia and their chromosome location

A

Presenilin 1 - chromosome 14
Presenilin 2 - chromosome 1
APP - chromosome 21

131
Q

Effect on APOE2 on AD

A

Protective

132
Q

Effect of APOE3 on AD

A

Neutral

133
Q

Effect of APOE4 on AD

A

Increases risk

134
Q

Where is APOE located?

A

Chromosome 19

135
Q

Which gene is associated with late onset dementia?

A

APOE

136
Q

Genes associated with Familial Frontotemporal Dementia

A

Progranulin

MAPT

137
Q

Genes potentially associated with Parkinson’s disease

A

SNCA - chromosome 4 - alpha-synuclein - dominant

Parkin - recessive inheritance

138
Q

Recurrence rate in siblings of autism inc. RR

A

2-8%

50x RR

139
Q

Heritability of ADHD

A

70-80%

140
Q

Genes linked to alcoholism

A

GABRA2 - chromosome 4
ADH4 - early onset regular drinking
DRD2

MRCPsych (19 decks)

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