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Psychiatry > Genetics > Flashcards

Genetics Flashcards

1
Q

What are the phases of the cell cycle?

A

G1 phase
S phase
G2 phase
M phase

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2
Q

What is the M phase

A

Mitosis phase

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3
Q

What happens to cells in the G0 phase?

A

Stimulated by growth factor, resulting in activation of transcription factors that lead to the initiation of DNA synthesis, followed by mitosis and cell division.

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4
Q

What happens in G1 phase?

A

Chromosomes are prepared for replication.

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5
Q

What happens in synthetic phase?

A

46 chromosomes are duplicated into chromatids

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6
Q

What happens in interphase?

A

Replication of cellular genetic material and organelles to prepare for next division

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7
Q

What is the longest phase in the cell cycle?

A

Interphase

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8
Q

Which steps in the cell cycle constitute the interphase?

A

G0
G1
G2
S

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9
Q

Stages of mitosis?

A

Prophase
Metaphase
Anaphase
Telophase

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10
Q

What happens during prophase?

A

Condensation of chromatin
breakdown of nuclear envelope
spindles at opposite cellular poles

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11
Q

What happens during metaphase?

A

Alignment of chromosomes

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12
Q

What happens during anaphase?

A

Separation of paired chromosomes

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13
Q

What happens during telophase?

A

Chromosomes are packed into distinct new nuclei in emerging daughter cells.
Cytokinesis (division of cytoplasm) also starts

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14
Q

What happens in Meiosis 2?

A

Same as normal mitosis

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15
Q

What is a acrocentric/submetacentric chromosome?

A

Centromere is at one end, so arms are of unequal length.

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16
Q

What is telocentric?

A

When centromere is at tail end of chromosome.

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17
Q

What is a holocentric chromosome?

A

Entire length of chromosome acts as centromere.

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18
Q

When types of chromosomes are not seen in humans?

A

Telocentric

Holocentric

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19
Q

What is an aneuploid cell?

A

When a cell possesses chromosomal numbers different from normal diploid status.

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20
Q

What failure results in triploidy/tetraploidy?

A

Non-disjunction - failure of chromosome/chromatid to separate in meiosis

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21
Q

Rate of Downs?

A

1:700

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22
Q

Prominent findings in Downs?

A

Reduced maternal levels of alpha-fetoprotein
Increased beta-hCG
Increased nuchal fold thickness in fetal USS

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23
Q

What is 95% of Downs attributed to?

A

Meiotic nondisjunction of homologous chromosomes,

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24
Q

What are 4% of Downs due to?

A

Robertsonian Translocation

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25
Q

What characterizes Edwards syndrome?

A 
Severe mental retardation
Rocker bottom feet
Low-set eats
Micrognathia (small jaw)
Congenital heart disease
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26
Q

Frequency of occurrence of Edwards syndrome?

A

1:8000

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27
Q

Which gender is Edwards syndrome more common in?

A

Three times more common in girls

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28
Q

Characteristics of Trisomy 13?

A 
Severe mental retardation
Microphthalmia
Microcephaly
Cleft lip/plate
Coloboma eye
Abnormal forebrain structures
Polydactyly
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29
Q

Rate of occurrence of Patau’s?

A

1:6000

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30
Q

Cause of Turners in 80%?

A

Origin of aneuploidy is from paternal X chromosome, so Turners is of maternal origin

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31
Q

Occurrence of Turners?

A

1:2000 live-born female infants

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32
Q

IQ profile of Turners?

A

Lower than general population by mean of 10 points (nearly one SD) due to reduced performance IQ
Verbal IQ preserved

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33
Q

What are the purine nucleic acids in DNA?

A

Adenine

Guanine

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34
Q

Difference between DNA and RNA?

A

RNA is single stranded in humans

DNA is double stranded

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35
Q

What is an exon?

A

Polypeptide coding sequences in DNA

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36
Q

Types of sequences in introns?

A

Satellite
Mini-satellite
Micro-satellite

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37
Q

When are introns removed?

A

ntrons are removed from mRNA before it leaves the nucleus and starts protein synthesis.

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38
Q

What is the name of synthesis of RNA from nuclear DNA?

A

Transcription

In cell nucleus

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39
Q

What is heterogeneous nuclear RNA?

A

Transcripted RNA which contains junk sequences (introns) that do not code for polypeptides,

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40
Q

Where are transfer RNAs synthesized

A

Synthesized from DNA in nucleus

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41
Q

What happens in termination?

A

Chain termination is signaled by one of three codons; UAA, UGA, UAG

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42
Q

What is modification?

A

Post-translational changes in a protein molecule before it becomes functionally active.

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43
Q

Where do modifications take place?

A

Endoplasmic reticulum

Golgi bodies

44
Q

Where does protein destruction occur?

A

Lysosome

45
Q

What is transcriptomic?

A

Study of mRNA using microchip arrays

46
Q

Define a mutation

A

Sudden, permanent and heritable change in DNA sequence

47
Q

What is a point mutation?

A

Single-base alteration in DNA

48
Q

What can lead to point mutations?

A

Substitution - one base replaced by another
Transition - if purine is replaced by another purine/pyrimidine with pyrimidine
Trans version - purine replaced by pyrimidine and vice versa

49
Q

What happens in frame mutation?

A

Changes in multiples of 3 bases, therefore no disturbance in actual reading frame

50
Q

Types of effects of mutations on protein product

A

Silent
Mis-sense
Nonsense

51
Q

What is a silent mutation?

A

No change in protein product

52
Q

What is a mis-sense mutation

A

New mutant codon specifies a different aa with variable effects in final protein.

53
Q

What happens in non-sense mutation?

A 
New codon is either:
UUA
UGA
UAG
which signal stop to aa sequence, therefore nonfunctional protein
54
Q

What are most translocations described as?

A

Reciprocal - one segment is exchanged for another segment among chromosomes

55
Q

What is the Robertsonian translocation?

A

Non-reciprocal (unequal exchange) resulting in single fused chromosome from 2 acrocentric chromosomes.

56
Q

Type of transmission of DiGeorge?

A

Autosomal dominant

57
Q

Risk of schizophrenia if offspring has deletion for DiGeorge?

A

25%

58
Q

Features of DiGeorge?

A 
Mild-moderate LD
Facial deformities (cleft palate)
Absent/malformed parathyroids leading to hypocalcaemia
Broad nasal bridge
Articulatory speech and swallow problems
59
Q

Location of transmission in Williams syndrome?

A

7q11 micro deletion

60
Q

Features of Williams syndrome?

A 
Hypercalcemia at birth
Supra valvular aortic stenosis
Moderate LD
Disinhibited disposition
Speech appears superficially fluent
Hyperacusis
61
Q

Features of Angelman syndrome?

A

Low IQ
Jerky movements - especially hand flapping
Frequent smiling
Seizures

62
Q

Features of Prader-Willi?

A 
Obesity
Short stature
Small limbs
Decreased IQ
Hyperphagia and skin pricking
63
Q

First law of Mendelian inheritance?

A

Law of uniformity;

if two organisms that differ in one trait are crossed, resulting hybrid will be uniform in that trait

64
Q

What is the second law of Mendelian inheritance?

A

Principle of segregation;
for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent to the offspring, based on chance

65
Q

What is the third law of Mendelian inheritance?

A

Principle of independent assortment;

66
Q

How does X inactivation occur?

A

DNA methylation

67
Q

What is unfavorable Lyonisation?

A

When during random X inactivation, most X chromosomes carrying normal alleles are inactivated

68
Q

What type of inheritance is Tuberous sclerosis?

A

AD

1 in 30000

69
Q

Features of Tuberous sclerosis

A 
Adenona sebaceum
Normal to severe MR (heart)
Ash leaf macules
Brain hamartomas
Heart and kidney cysts
70
Q

Features of Apert syndrome?

A 
Variable MR
Cranio synostosis
Shallow orbits
Trapezoid mouth
Mitten hands and feet
AD
71
Q

Inheritance of Noonan syndrome?

A

AD

Chromosome 12

72
Q

Risk of Noonan syndrome?

A

1 in 1500

73
Q

Features of Noonan syndrome

A 
Mild MR
Short stature
Nuchal oedema/webbed neck
Pulmonary stenosis
Cryptorchidism
74
Q

Type of inheritance of Lesch-Nyhan syndrome

A

X linked recessive

75
Q

Features of Lesch-Nyhan syndrome

A

Poor muscle control
Moderate mental retardation - year 1
Self-mutilating behaviour - lip and finger biting
Hyperuricaemia and Hyperuricosuria (gout and kidney problems)

76
Q

Give e.g. of X-linked inheritance

A

Haemophilia A/B
Duchenne Muscular Dystrophy
Androgen insensitivity syndrome

77
Q

Commonest cause of blindness in young men?

A

Commonest cause of blindness in young men?

78
Q

Examples of Trinucleotide repeat disorders

A

Fragile X
Friedreich Ataxia
Huntingtons
Myotonic dystrophy

79
Q

Where is the mutation in Fragile X?

A

CGG

80
Q

Where is the mutation in Friedreich?

A

GAA

81
Q

Where is the mutation in myotonic dystrophy?

A

CTG

82
Q

Which two conditions result in most cases of mental retardation in males?

A

Downs

Fragile X

83
Q

Which gene results in Fragile X?

A

Expansion of CGG proximal to FMR1 gene

84
Q

Features of Fragile X (male)

A 
Enlarged testes
Prominent ear lobes
Protracting jaw
High pitched voice
Mental retardation
85
Q

What are premutant carriers of Fragile X at risk of?

A

Developing intention tremor and ataxia after middle taxia

86
Q

What are premutation carriers in Fragile X?

A

Those who carry increased number of CGG repeats in FMR1 locus but do not have clinical phenotype

87
Q

What are women who are premutation carriers for Fragile X at risk of?

A

Premature ovarian failure

Mild cognitive/behavioral abnormalities

88
Q

Prevalence of Huntington’s?

A

5 per 100000

89
Q

What is the gene that causes Huntington’s?

A

Expanded and unstable CAG trinucleotide repeat on short arm of chromosome 4-4p16.3

90
Q

What is genomic imprinting?

A

Where the disease phenotype expressed depends on whether allele is maternally or paternally inherited.

91
Q

What is polymorphism?

A

Variations in genetic make-up at a particular locus noted in the healthy population - at least in 1% of population

92
Q

What are single nucleotide polymorphisms?

A

If polymorphism is to due to change in single nucleotide in a sequence.

93
Q

How can single based polymorphisms be assayed?

A

DNA sequencing

DNA chips

94
Q

What are variable number of tandem repeats?

A

Polymorphism due to varying number of repeats in specific region of chromosome.

95
Q

How are variable number of tandem repeats classified?

A

Short tandem repeat polymorphism
Microsatellite (2-6 bases)
Minisatellite (20-bases)

96
Q

Where do most polymorphisms occur in a gene?

A

Introns

97
Q

Features of those with short allele of 5HTTLPR?

A

Low expression of serotonin transporter

98
Q

What is short variant of 5HTTLPR speculated to be linked to?

A

Higher incidence of affective disorders, neuroticism, anxiety and PTSD

99
Q

When is southern blotting used?

A

For detecting specific sequence of DNA

100
Q

When is western blotting used?

A

Detection of specific protein after electrophoresis

101
Q

When is northern blotting used?

A

Detection method for specific RNA after electrophoresis.

102
Q

What does PCR do?

A

Amplifies minute amounts of DNA, allowing further analysis

103
Q

What does the Hardy Weinberg equilibrium determine?

A

The frequency of an abnormal gene or genotype in the population.

104
Q

What is epistasis?

A

Gene-gene interaction, particularly between different alleles

105
Q

What is locus heterogeneity?

A

When same disease phenotype can be caused by mutations in different loci.

106
Q

What is allelic heterogeneity?

A

Same disease phenotype resulting form different types of mutations at same loci.

107
Q

What is pleiotropy

A

When single disease-causing mutation affects multiple organ systems.

Psychiatry (10 decks)

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