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MRCPsych Part A small > Molecular genetics > Flashcards

Molecular genetics Flashcards

1
Q

Component of the cell that is responsible for the synthesis of lipids and proteins

A

Endoplasmic reticulum

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2
Q

Component of the cell that is responsible for intracellular degradation

A

Lysosome

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3
Q

Component of the cell that contains DNA

A

Nucleus

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4
Q

Component of the cell responsible for oxidation of toxic molecules

A

Peroxisome

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5
Q

Component of the cell responsible for the modification, sorting and packaging of lipids and proteins

A

Golgi apparatus

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6
Q

Component of the cell that is the site of adenosine triphosphate (ATP) synthesis by oxidative phosphorylation

A

Mitochondria

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7
Q

Restriction point (in the cell cycle) - definition

A

This is the point at which the cell no longer requires growth factors to progress through the cell cycle.

It occurs at the end of G1. From this point, the cell is committed to entering S phase.

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8
Q

Cell cycle phases (4)

A

G1 (Gap 1)
S (synthesis
G2 (Gap 2)
M (mitosis)

  • G1, S, and G2 are collectively known as ‘Interphase’

Interphase - preparation of the cell for division
Mitosis - actual cell division

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9
Q

Gap 1 phase (essence)

A

Preparing the cell for DNA synthesis

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10
Q

Synthesis (S) phase (essence)

A

DNA replication

By the end of this phase, each chromosome is replicated into two identical chromatids

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11
Q

Gap 2 phase (essence)

A

Preparing the cell for mitosis

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12
Q

Mitosis - stages (6)

A 
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
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13
Q

Which stage of mitosis?:

Chromatin condenses and becomes visible as chromosomes

A

Prophase

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14
Q

Which stage of mitosis?:

The nuclear membrane dissolves and microtubules become attached to the centromeres

A

Prometaphase

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15
Q

Which stage of mitosis?:

Chromosomes become aligned at the middle of the cell (cell equator);
Spindle fibres attach each sister chromatid to an opposite pole

A

Metaphase

Metaphase - M for ‘Middle’ (of the cell, where the chromosomes are aligned)

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16
Q

Which stage of mitosis?:

Paired chromosomes separate and begin moving to opposite ends of the cell

A

Anaphase

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17
Q

Which stage of mitosis?:

Chromatids arrive at opposite poles of the cell and new nuclear membranes begin to form around them

A

Telophase

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18
Q

Which stage of mitosis?:

The cell splits into two daughter cells each with a nucleus

A

Cytokinesis

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19
Q

Meiosis (essence)

A

Divided into Meiosis I and II

Meiosis I - ‘reduction division’

  • in a prolonged prophase I, homologous maternal and paternal chromatid pairs line up and exchange genetic material in a process called ‘crossing over’
  • in anaphase I, chromatid pairs remain attached
  • the products of meiosis I are 2 haploid cells

Meiosis II - ‘mitosis for haploid cells’

  • essentially the same as mitosis, except without the prior S phase DNA replication
  • therefore the product is 4 haploid cells
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20
Q

Chromosome structure

  • centromere
  • telomere
  • short arm
  • long arm
A

A centromere links a pair a sister chromatids

Arms protrude from the centromere:

  • short arm = p
  • long arm = q

Telomere - a region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes

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21
Q

Number of chromosomes in human diploids cells

A

46

  • 22 pairs of autosomes
  • 1 pair of sex chromosomes
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22
Q

Chromosome abnormalities - deletions (definition & examples, 4)

A

Genetic material is lost from a single chromosome

  • Terminal deletion
  • Ring chromosomes
  • Interstitial deletions
  • Microdeletions
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23
Q

A single break occurs and the broken chromosome end is capped by a telomere

A

Terminal deletion

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24
Q

Both ends of the chromosome are lost and the broken ends fuse

A

Ring chromosome

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25
Q

Two breaks occur in the chromosome and the segment between them is lost

e.g. chromosome 15 in Prader-Willi and Angelman syndromes

A

Interstitial deletion

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26
Q

Small interstitial deletion in a chromosome that is not detectable microscopically

e.g. chromsome 22 in DeGeorge syndrome

A

Microdeletion

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27
Q

Chromosome abnormalities - translocation (definition + examples, 3)

A

Breaks occur in two different chromosomes and genetic material is exchanged

  • Reciprocal translocation
  • Robertsonian translocation
  • Sex chromosome-autosome translocation
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28
Q

A single break occurs in two different chromosomes and the terminal ends are exchanged

A

Reciprocal translocation

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29
Q

The long arm of two different chromosomes fuse, with loss of the genetic material on the short arms

occurs in Downs syndrome on chromosome 21

A

Robertsonian translocation

Acrocentric chromosomes are most susceptible to this

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30
Q

Genetic material is exchanged between a sex chromosome and an autosome

A

Sex chromosome-autosome translocation

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31
Q

Chromosome abnormalities - inversion (definition & examples, 2)

A

Two breaks occur in the same chromosome and the ends are swapped

  • Paracentric - both breaks in same arm
  • Pericentric - breaks in different arms
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32
Q

Aneuploidy (definition, examples)

A

Gain or loss of a single chromosome e.g.

  • Trisomy - three copies of one chromosome, e.g. Trisomy 21 (Down’s syndrome)
  • Monosomy - one copy of a chromosome e.g. monosomy X (Turner syndrome)
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33
Q

DNA/RNA base pairs (summary)

A

DNA: ‘GCAT’

  • Guanine pairs to Cytosine
  • Adenine pairs to Thymine

RNA: ‘GCAU’
- Thymine is replaced by Uracil

Purines: G & A
Pyrimidines: C, T & U

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34
Q

DNA base pairs - Purines

A

Guanine

Adenine

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35
Q

DNA base pairs - Pyrimidines

A

Cytosine
Thymine
Uracil

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36
Q

DNA nucleotide - components (3)

A

Five-carbon deoxyribose sugar
Phosphate group
Nitrogenous Base

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37
Q

RNA - types (3)

A 
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
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38
Q

… carries information from DNA to structures called ribosomes.

These ribosomes are made from proteins and ribosomal RNAs, which come together to form a molecular machine that can read … and translate the information they carry into proteins.

A

Messenger RNA (mRNA)

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39
Q

… brings amino acids to the ribosome during translation, allowing them to be incorporated into a protein

A

Transfer RNA (tRNA)

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40
Q

… is what ribosomes are made up of and provides a place for mRNA and tRNA to attach during translation

A

Ribosomal RNA (rRNA)

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41
Q

Gene (essence)

A

The basic unit of heredity

Physically, it is a length of nucleotides within a chromosome - each gene has ~27,000 nucleotide pairs

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42
Q

Exon

A

The part of a gene (~1300 nucleotide pairs) that codes for a protein

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43
Q

Intron

A

The part of a gene that does not code for a protein

(most of a genes’ ~27,000 nucleotide pairs are part of the intron)

‘INtrons are not translated INto protein’

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44
Q

Transcription (essence)

A

the process by which an RNA polymerase sequences an mRNA molecule from a DNA template

remember: ‘transcribe’ means to make a full written copy

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45
Q

Transcription - main steps (3)

A

Initiation
- binding of RNA polymerase to double-stranded DNA, RNA polymerase binds at a sequence of DNA called the promoter

Elongation

  • the development of a short stretch of DNA that is transiently single-stranded
  • an mRNA copy of the DNA coding strand is produced, in which thymine is replaced by uracil

Termination
- the recognition of the transcription termination sequence and the release of RNA polymerase

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46
Q

Translation (essence)

A

the process by which a protein is synthesised from its mRNA intermediary in the cytoplasm (in a ribosome)

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47
Q

Translation - process

A
  • consecutive groups of 3 nucleotides are called codons - they correspond to the 20 common amino acids, and initiation and stop codons
  • tRNA, synthesised in the nucleus, enters the cytoplasm attached to specific amino acids

3 steps:

  • a tRNA molecule, to which an amino acid is attached, binds to the mRNA strand via an anticodon
  • another tRNA molecule enters the ribosome and binds to the next three mRNA bases - the ribosome then links together the amino acids via a peptide bond
  • the tRNAs dissociate and go off to collect more amino acids. The process then repeats to extend the protein chain
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48
Q

Start codon for translation

+ amino acid it codes for

A

AUG

Methionine

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49
Q

Stop codons for translation (3)

A

UAA
UAG
UGA

‘oo-ah, oo-ag, oo-ga’

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50
Q

Modification (essence)

A

post-translational changes to a protein - affecting its structure, stability and function

takes place in the endoplasmic reticulum, golgi apparatus and secretory vesicles

most common type is protein cleavage

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51
Q

Tandem repeat - definition and examples (3)

A

These occur when a nucleotide sequence is replicated into numerous adjacent repeats.

  • Microsatellites
  • Minisatellites
  • Satellites
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52
Q

Microsatellite

A

a tandem repeat of <9 nucleotides, repeated between 5-40 times

  • occupy 3% of the human genome
  • most common form is a dinucleotide repeat - e.g. CACACACACACACACA
  • they are unstable and have a mutation rate >10x the rest of the genome
  • this high mutation rate allows genetic distance between individuals to be estimated and is used in linkage analysis
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53
Q

Minisatellite

A

a tandem repeat of >9 nucleotides

much less common than microsatellites

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54
Q

Satellite DNA sequence

A

a tandem repeat of >200 nucleotides, repeated hundreds of times

  • occupy 5% of the human genome
  • they are a major component of heterochromatin and centromeres
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55
Q

Repetitive DNA - 2 kindsq

A

Tandem repeats

Dispersed repeats

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56
Q

Dispersed repeat (essence)

A

Repeated nucleotide sequences randomly spread in the genome

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57
Q

the complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria.

A

The human genome

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58
Q

A heritable change at a single base

A

Point mutation

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59
Q

… occurs when one base nucleotide is swapped for another during DNA replication

A

Substitution

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60
Q

A purine/purine substitution

A

Transition

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61
Q

A purine/pyramidine substitution

A

Transversion

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62
Q

A point mutation in which the new codon codes for the same amino acid, therefore the end protein is unchanged

A

Silent (synonymous) mutation

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63
Q

A point mutation in which the codon is transformed into a termination code that prematurely truncates the protein

A

Nonsense mutation

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64
Q

A point mutation in which the codon is changed to code for a different amino acid

A

Missense (nonsynonymous mutation)

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65
Q

This kind of mutation occurs when the new amino acid has similar properties to the old one

A

Conservative mutation

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66
Q

This kind of mutation occurs when the new amino acid has different properties, causing a reduction or even loss of protein functioning

A

Non-conservative mutation

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67
Q

… occurs when one or more nucleotide base is added to a DNA strand

A

Insertion

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68
Q

… occurs when one or more nucleotide base is deleted from a DNA strand

A

Deletion

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69
Q

Frame shift mutation (essence)

A
  • the genetic code is read by translating groups of 3 nucleotides into a single amino acid
  • any mutation that adds or deletes a sequence of nucleotides not divisible by three alters the reading frame
  • every codon read after the mutation is altered. Thus, the earlier in the gene the mutation occurs, the larger the effect on the protein
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70
Q

This kind of mutation does not alter the reading frame

A

In-frame mutation

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71
Q

This kind of mutation occurs when a STOP codon is mutated into one encoding an amino acid. The translation machinery continues to extend the amino acid chain until the next STOP codon is reached

A

Readthrough mutation

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72
Q

Trinucleotide repeat (essence)

A

A form of tandem repeat.

A sequence of three nucleotides is repeated multiple times adjacent to one another.

Abnormal expansion of trinucleotide repeats above the stable threshold for a gene is linked to higher occurrence of genetic disease

The most well-recognised of these are the polyglutamine diseases (repeat CAG)

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73
Q

The phenomenon by which the number of trinucleotide repeats increases along with disease severity with each subsequent generation

A

Anticipation

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74
Q

Huntingdon’s disease

inheritance pattern, genetic pathology

A

Adult-onset autosomal dominant

Trinucleotide repeat of CAG on chromosome 4p

=============================
Normally CAG is repeated less than 27 times

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75
Q

Conditional mutations - essence + subtypes (3)

A

The effect of a mutation depends, in some situations, on the environmental conditions surrounding the organism.

  • Unconditionally deleterious mutations
  • Conditionally neutral mutations
  • Conditionally beneficial mutations
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76
Q

This kind of mutation:

  • impairs the essential functioning of the organism
  • is deleterious in all environments
  • is purged by natural selection
A

Unconditionally deleterious mutation

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77
Q

A kind of mutation that is only deleterious in some environments, and neutral in others

A

Conditionally neutral mutation

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78
Q

A kind of mutation that is beneficial in some environments i.e. they increase the organism’s fitness, but deleterious in other environments

e.g. the sickle cell anaemia gene is protective against malarial infection

The mutation persists through natural selection in populations exposed to the stressful environment

A

Conditionally beneficial mutation

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79
Q

The DNA sequence defining the set of genes an organism carries, or the pair of alleles at a specific genetic locus

A

Genotype

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80
Q

An individual’s observable traits (such as height, eye colour, and blood type) which results from the interaction between the genotype and the environment.

A

Phenotype

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81
Q

The proportion of individuals carrying a particular variant (or allele) of a gene (the genotype) that also express an associated trait (the phenotype).

The probability of a gene or genetic trait being expressed.

A

Penetrance

Most genes associated with psychiatric disorders show low penetrance

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82
Q

… quantifies variation in a non-binary phenotype across individuals carrying a particular genotype. It is equal to the proportion of individual carriers of a genotype for a trait who show the trait to a specifiable extent

A

Expressivity

Most psychiatric disorders, such as autism, show variable expression

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83
Q

Hardy-Weinberg Equilibrium (essence)

A

The phenomenon whereby allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.

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84
Q

Conditions necessary for maintenance of Hardy-Weinberg equilibrium (5)

A
  • No mutations must occur, so that new alleles do not enter the population.
  • No gene flow can occur (no migration of individuals into, or out of, the population).
  • No non-random mating - no assortative mating (mating based on phenotype), no consanguinity (mating of blood relatives)
  • No genetic drift (random chance) can cause the allele frequencies to change (i.e. population must be sufficiently large to prevent this)
  • No natural selection must occur - differences in genotype do not confer disparate survival or reproductive success on an individual
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85
Q

This law states that every individual organism contains two alleles for each trait, and that these alleles separate during meiosis such that each gamete contains only one of the alleles. An offspring thus receives a pair of alleles for a trait by inheriting homologous chromosomes from the parent organisms: one allele for each trait from each parent.

A

The law of segregation (Mendel’s first law)

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86
Q

This law states that alleles for separate traits are passed independently of one another. That is, the biological selection of an allele for one trait has nothing to do with the selection of an allele for any other trait.

A

The law of independent assortment (Mendel’s second law)

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87
Q

Which pattern of inheritance?:

  • Heterozygotes display the disease phenotype
  • In family trees, the disease is present in every generation (vertical transmission)
  • If a parent is homozygous for the disease-causing allele (AA), 100% of their offspring will inherit it
  • If a parent is heterozygous for the disease-causing allele (Aa), 50% of their offspring will inherit it
A

Autosomal dominant

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88
Q

Noonan’s disease

inheritance pattern and genetic pathology

A

Autosomal dominant

Disease gene lies on chromosome 12q

think ‘noon’ is 12pm i.e. chromosome 12

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89
Q

Which pattern of inheritance?:

  • Only homozygotes display the disease phenotype
  • Heterozygotes are carriers
  • In family trees, the disease may not be present in every generation
  • Displays horizontal transmission
A

Autosomal recessive

90
Q

Louis Bar syndrome
aka ataxia telangiectasia
(inheritance pattern and genetic pathology)

A

Autosomal recessive

Disease gene lies on chromosome 11p

91
Q

X-inactivation

aka, essence, key facts

A

aka Lyonisation

this is the random inactivation of one X chromosome in each cell of a female, whose daughter cells then inherit the same pattern

  • occurs early in embryogenesis (at 16-32 cells), via DNA methylation
  • affects most but not all genes on the inactivated X chromosome - 20% are still expressed
  • the inactivated X chromosome is maintained in a silent state called a Barr Body
92
Q

Barr Body

A

This is the inactivated X chromosome within the cells of a female

93
Q

Which pattern of inheritance?:

  • Males and females are both affected, with males typically being more severely affected than females
  • An affected father can never pass the disease to his sons; but all daughters will be affected
  • A woman with the disorder has a 50% chance of having an affected foetus
A

X-linked dominant

94
Q

Which pattern of inheritance?:

  • Males are more frequently affected than females
  • Transmitted through carrier females to their sons (knights move pattern)
  • Affected males cannot pass the condition onto their sons
  • A woman who is a carrier has a 50% chance of having sons who are affected and a 50% chance of having daughters who are carriers
A

X-linked recessive

95
Q

Fragile X syndrome

inheritance pattern and genetic pathology

A

X-linked dominant

Abnormal CGG trinucleotide repeats on the long arm of the X chromosome

96
Q

Which inheritance pattern?:

  • Every son of an affected father will be affected
  • Female offspring of affected fathers are never affected
A

Y-linked

97
Q

In this inheritance pattern, an organism’s phenotype depends on small additive effects of a large number of genetic variants

A

Polygenic inheritance

98
Q

In this inheritance pattern, an organism’s phenotype depends on the combined effect of a small number of genetic variants

A

Oligogenic inheritance

99
Q

Heritability (definition)

A

The proportion of the variation in a phenotype within a population that is due to variation in genotype

NB: heritability does NOT concern individuals, but rather population-level variations

100
Q

Alzheimer’s disease - Heritability (%)

A

60%

101
Q

ADHD - Heritability (%)

A

80%

102
Q

Alcohol dependence - Heritability (%)

A

50-60%

103
Q

Anorexia - Heritability (%)

A

55%

104
Q

Autistic spectrum disorder - Heritability (%)

A

90%

105
Q

Bipolar disorder - Heritability (%)

A

80-95%

===============
SPMM says 75%-80%

106
Q

Major depressive disorder - Heritability (%)

A

35-50%

107
Q

Schizophrenia - Heritability (%)

A

80-85%

108
Q

OCD - Heritability (%)

A

25-50%

109
Q

Panic disorder - Heritability (%)

A

45%

110
Q

This form of inheritance involves heritable changes to gene expression that are not caused by alterations to the DNA sequence

A

Epigenetic inheritance

111
Q

Risk of schizophrenia in a monozygotic twin (%)

A

48%

112
Q

This kind of study is used to determine the genetic location of a disease gene, and utilises the principle of linkage disequilibrium.

The goal is to identify a piece of DNA of known location that is inherited by all family members affected by the disorder being studied, and is not inherited by any of the unaffected family members. Once this piece of DNA is found, one knows that the disease gene must lie somewhere close by.

A

Linkage analysis

113
Q

LOD Score

A

Logarithm of the odds - a statistic used in Linkage Analysis

a statistical estimate of whether two genes, or a gene and a disease gene, are likely to be located near each other on a chromosome and are therefore likely to be inherited

By convention:
>3 is considered evidence for linkage

114
Q

Linkage disequilibrium

A

the tendency of alleles to be inherited together due to their proximity on the same chromosome

115
Q

This kind of study is used to determine the pattern of inheritance for a trait.

A

Segregation analysis

116
Q

Early-onset Familial Alzheimer’s Disease (EOFAD) - associated genes (3)

A

amyloid precursor protein (APP)
- accounts for 10-15% of EOFAD

presenilin one (PSEN-1)
- accounts for 30-70% of EOFAD
presenilin two (PSEN-2)
- accounts for 5% of EOFAD
117
Q

APP gene (location and association)

A

Chromosome 21

Accounts for 10-15% of Early-onset Familial Alzheimer’s Disease (EOFAD)

118
Q

PSEN-1 gene (location and association)

A

Chromosome 14

Accounts for 30-70% of Early-onset Familial Alzheimer’s Disease (EOFAD)

119
Q

PSEN-2 gene (location and association)

A

Chromosome 1

Accounts for 5% of Early-onset Familial Alzheimer’s Disease (EOFAD)

120
Q

Late onset Alzheimer’s disease - associated gene (1 + function)

A

apolipoprotein E (APOE)

APOE is thought to be involved in the breakdown of amyloid plaques and different forms of it seem to vary in how effective they can do this.

121
Q

APOE gene - location, alleles (3) + their association with risk of alzheimer’s

A

Chromosome 19

APOE2 - protective
APOE3 - neutral
APOE4 - increases risk of late onset Alzheimer’s

  • Heterozygous - 3x increased risk
  • Homozygous - 10-30x increased risk
  • each E4 allele lowers the age of onset by 10 years.
122
Q

a set of DNA variations, or polymorphisms, that tend to be inherited together

A

Haplotype

123
Q

an individual’s collection of chromosomes

A

karyotype

124
Q

Pleiotropy (essence)

A

when one gene influences two or more seemingly unrelated phenotypic traits

125
Q

3 aneuploidies compatible with life (+chromosomes involved)

A

Trisomy 21 (Down’s syndrome) - 1 in 800 births

Trisomy 18 (Edwards syndrome) - 1 in 6000 births

Trisomy 13 (Patau syndrome) - 1 in 10,000 births

126
Q

Prader-Will Syndrome (genetic pathology)

A

deletion of genetic material from the chromosome 15 (15q11-13) inherited of paternal origin

is a classic example of imprinting

127
Q

Prader-Will Syndrome (features)

A

Hyperphagia (excessive eating) and obesity
Short stature
Delayed puberty, hypogonadism, infertility
Learning difficulties
Compulsive behaviour (e.g. skin picking)

128
Q

APOE4 - risk of late onset Alzheimer’s

  • heterozygous
  • homozygous
A
  • Heterozygous - 3x increased risk
  • Homozygous - 10-30x increased risk
  • each E4 allele lowers the age of onset by 10 years.
129
Q

Downs Syndrome (genetic pathology)

A

Trisomy 21

Short stature, simian crease, almond shaped eyes due to epicanthic folds, upslanting palpebral fissures, low set ears, brushfield spots, and poor muscle tone. Most have mild (IQ 50-70) to moderate (IQ 35-50) mental retardation

130
Q

Name the condition:

Short stature
simian crease, almond shaped eyes due to epicanthic folds
upslanting palpebral fissures
low set ears
brushfield spots
poor muscle tone.

Most have mild (IQ 50-70) to moderate (IQ 35-50) mental retardation

A

Downs syndrome (trisomy 21)

131
Q

Angelman syndrome

aka, genetic pathology

A

Happy puppet syndrome

15q11 maternal origin

Flapping hand movements (uplifted, flexed arms when walking), ataxia, pronounced verbal delay (compared to comprehension), serveve to profound learning disability, seizures and sleep problems

132
Q

Name the condition:

Flapping hand movements (uplifted, flexed arms when walking)
ataxia
pronounced verbal delay (compared to comprehension)
servere to profound learning disability
seizures
sleep problems

A

Angelman syndrome
aka Happy puppet syndrome

15q11 maternal origin

133
Q

Prader-Willi Syndrome (genetic pathology)

A

15q11 paternal origin

Hyperphagia, excessive weight gain, short stature, frequent skin picking, mild learning disability, small gonads, and hypotonia

134
Q

Name the condition:

Hyperphagia
excessive weight gain
short stature
frequent skin picking
mild learning disability
small gonads
hypotonia
A

Prader-Willi Syndrome

15q11 paternal origin

135
Q

Cri du chat (genetic pathology)

A

5p deletion

Characteristic cry like a meowing kitten, hypotonia, hypertelorism, a down-turned mouth, and microcephaly

136
Q

Name the condition:

Characteristic cry like a meowing kitten
hypotonia
hypertelorism
down-turned mouth
microcephaly
A

Cri du chat

5p deletion

137
Q

Di George syndrome

aka, genetic pathology

A

aka Velocardiofacial syndrome

22q deletion

Cleft palate, cardiac problems, and learning disabilities. A higher rate of psychiatric disorders is also seen
Hypoparathyroidism leading to hypocalcemia (60%)

138
Q

Name the condition:

Cleft palate, cardiac problems, and learning disabilities. A higher rate of psychiatric disorders is also seen
Hypoparathyroidism leading to hypocalcemia (60%)

A

Di George syndrome
aka Velocardiofacial syndrome

22q deletion

139
Q

Edwards’s syndrome (genetic pathology)

A

Trisomy 18

Kidney malformations, upturned nose, webbing of second and third toes, and clubbed feet (rocker bottom)

140
Q

Name the condition:

Kidney malformations
upturned nose
webbing of second and third toes
clubbed feet (rocker bottom)

A

Edwards’s syndrome

Trisomy 18

141
Q

Lesch-Nyhan syndrome (genetics pathology)

A

Xq26-27

(mutations in the HPRT gene)

Self mutilation, dystonia and writhing movements
hyperuricemia

142
Q

Name the condition:

Self mutilation, dystonia and writhing movements
hyperuricemia

A

Lesch-Nyhan syndrome

Xq26-27
mutations in the HPRT gene

143
Q

Smith-Magenis syndrome (genetic pathology)

A

17p11 (microdeletion)

Pronounced self injurious behaviour, self hugging, and a hoarse voice

144
Q

Name the condition:

Pronounced self injurious behaviour
self hugging
hoarse voice

A

Smith-Magenis syndrome

17p11 (microdeletion)

145
Q

Fragile X Syndrome (genetic pathology)

A

Abnormal CGG trinucleotide repeats on the long arm of the X chromosome

Elongated face, large ears, large testicles, hand flapping, shyness, and little eye contact

146
Q

Name the condition:

Elongated face
large ears
large testicles
hand flapping
shyness and little eye contact
A

Fragile X Syndrome

Abnormal CGG trinucleotide repeats on the long arm of the X chromosome

(X-linked dominant inheritance)

147
Q

Wolf Hirschhorn syndrome (genetic pathology)

A

4p deletion

Profound mental retardation, microcephaly, seizures, down turned fishlike mouth, Greek warrior helmet face, and cleft lip

148
Q

Name the condition:

Profound mental retardation
microcephaly
seizures
down turned fishlike mouth
Greek warrior helmet face
cleft lip
A

Wolf Hirschhorn syndrome

4p deletion

149
Q

Patau syndrome (genetic pathology)

A

Trisomy 13

Mental retardation, polydactyl, microcephaly, overlapping of fingers over thumb

150
Q

Name the condition:

Mental retardation
polydactyl
microcephaly
overlapping of fingers over thumb

A

Patau syndrome

Trisomy 13

151
Q

Rett syndrome (genetic pathology, inheritance)

A

Xq28
(genetic mutation of the MECP2 gene)

X-linked dominant

Normal for the first 12 months. Regression and loss of skills from around 18 months onwards. Hand-wringing movements are the most common feature. Associated learning disability is profound. Affects girls almost exclusively

152
Q

Name the condition:

Normal for the first 12 months.
Regression and loss of skills from around 18 months onwards.
Hand-wringing movements are the most common feature.
Associated learning disability is profound.
Affects girls almost exclusively

A

Rett syndrome

Xq28
genetic mutation of the MECP2 gene

153
Q

Tuberous sclerosis (genetic pathology)

A

Genetically heterogenous - mutation of either of two genes:

  • TSC1 (9q)
  • TSC2 (16p)

Hamartomatous tumours affect various organs including the brain. 80% suffer with epilepsy. Autism, ADHD, and sleep problems are common

154
Q

Name the condition:

Hamartomatous tumours affect various organs including the brain.
80% suffer with epilepsy.
Autism
ADHD
sleep problems
A

Tuberous sclerosis

Genetically heterogenous - mutation of either of two genes:
- TSC1 (9q)
- TSC2 (16p)

155
Q

Williams syndrome (genetic pathology)

A

7q11 deletion

Elfin like features, social disinhibition, and abnormal friendliness towards strangers. Very sensitive hearing is also seen. Advanced verbal skills, speech is articulate but superficial (referred to as cocktail party speech)

156
Q

Name the condition:

Elfin like features
social disinhibition
abnormal friendliness towards strangers
Very sensitive hearing
Advanced verbal skills - speech is articulate but superficial (referred to as cocktail party speech)
A

Williams syndrome

7q11 deletion

157
Q

Rubinstein-Taybi syndrome (genetic pathology)

A

Unclear, 16p deletions have been reported

Tend to be short with small heads. Associated with a friendly disposition and moderate learning disability

158
Q

Name the condition:

Tend to be short with small heads.
Associated with a friendly disposition and moderate learning disability

A

Rubinstein-Taybi syndrome

Unclear, 16p deletions have been reported

159
Q

Klinefelter syndrome (genetic pathology)

A

Extra X chromosome in phenotypic males (47 XXY)

Tend to be tall with small testicles. Typically introverted with poor social and school performance

160
Q

Name the condition:

Tend to be tall with small testicles.
Typically introverted with poor social and school performance

A

Klinefelter syndrome

Extra X chromosome in phenotypic males (47 XXY)

161
Q

Jacob’s syndrome (aka, genetic pathology)

A

aka ‘Super-males’, XYY Syndrome

Extra Y chromosome (47 XYY)

It is usually asymptomatic. Affected individuals tend to be taller than average. Testosterone levels are normal and fertility and sexual development are usually unaffected.

There is an increased risk of learning difficulties. Aggression is not seen in higher levels than the normal population.

162
Q

Name the condition:

usually asymptomatic
Affected individuals tend to be taller than average.
Testosterone levels are normal and fertility and sexual development are usually unaffected.
There is an increased risk of learning difficulties. Aggression is not seen in higher levels than the normal population.

A

Jacob’s syndrome

aka ‘Super-males’, XYY Syndrome

163
Q

Coffin-Lowry syndrome (genetic pathology)

A

Xp22 (mutations)

Short stature, slanting eyes with short broad nose. Severe learning difficulty

164
Q

Name the condition:

Short stature, slanting eyes with short broad nose. Severe learning difficulty

A

Coffin-Lowry syndrome

Xp22 (mutations)

165
Q

Turner syndrome (genetic pathology)

A

45 X0

Short stature
Webbed neck
Broad chest (widely spaced nipples)
Gonadal dysfunction (amenorrhoea and infertility)
Congenital heart disease (cardiac malformation in approx 1/3 of cases)
Hypothyroidism

166
Q

Name the condition:

Short stature
Webbed neck
Broad chest (widely spaced nipples)
Gonadal dysfunction (amenorrhoea and infertility)
Congenital heart disease (cardiac malformation in approx 1/3 of cases)
Hypothyroidism

A

Turner syndrome

45 X0

167
Q

Niemann Pick disease (types A and B)

genetic pathology

A

11p15

(Mutations in the SMPD1 gene)
Abdominal swelling, cherry red spot, feeding difficulties

168
Q

Name the condition:

Abdominal swelling, cherry red spot, feeding difficulties

A

Niemann Pick disease (types A and B)

11p15
Mutations in the SMPD1 gene

169
Q

The total number of possible different codons that can occur in a human DNA is —

A

64

170
Q

First-degree relatives share — of their genes.
Second-degree relatives share —
Third-degree relatives share —

A

50%
25%
12.5%

171
Q

The gene that encodes the serotonin transporter

+ location (chromosome)

A

SLC6A4
(solute carrier family 6 member 4)

chromosome 17
(17q11.1-q12)

172
Q

Lifetime risk of unipolar depression in a member of the general population (unrelated to anyone with affective disorder) (%)

A

5-10%

173
Q

Lifetime risk of unipolar depression in a first-degree relative of someone with bipolar disorder (%)

A

10-20%

2-3 times higher than general population

174
Q

Lifetime risk of unipolar depression in a monozygotic twin of someone with bipolar disorder (%)

A

15-25%

3-5 times higher than general population

175
Q

Haploid
Diploid
Triploid

A

Haploid - one set of chromosomes (23)
Diploid - two sets of chromosomes (46)
Triploid - three sets of chromosomes (69)

176
Q

Catechol-O-methyl transferase (COMT) enzyme

  • chromosomal locus
A

22q11

177
Q

Polymorphism

essence

A

Polymorphisms are natural variations in a gene, DNA sequence, or chromosome that have no adverse effects on the individual and occur with fairly high frequency in the general population.

A gene is said to be polymorphic if more than one allele occupies that gene’s locus within a population.[1] In addition to having more than one allele at a specific locus, each allele must also occur in the population at a rate of at least 1% to generally be considered polymorphic.

178
Q

Epigenetic variation

- common processes (2)

A

DNA methylation

Histone modification

179
Q

Nucleotide vs Nucleoside

A

Nucleoside:

  • 5-carbon sugar
  • nitrogenous base

Nucleotide:

  • Five-carbon deoxyribose sugar
  • Phosphate group
  • Nitrogenous Base

Therefore - Nucleoside + Phosphate = Nucleotide

180
Q

Compared with general population, relative risk of alcoholism is increased by — if there is a strong family history

A

x4-6

181
Q

In translation, which enzyme mediates the binding of tRNA with amino acids?

A

aminoacyl-tRNA synthetase

This synthetic process is called aminoacylation

182
Q

In — individuals with similar phenotypes mate with one another more frequently than would be expected under a random mating pattern.

A

Assortive mating

183
Q

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

A

2%

==============================
More than 98% of the human genome does not encode protein sequences, including most sequences within introns and most intergenic DNA

184
Q

— is the phenomenon where the effect of one gene (locus) is dependent on the presence of one or more ‘modifier genes’, i.e. the genetic background.

A

Epistasis

185
Q

— is the failure of homologous chromosomes or sister chromatids to separate properly during cell division.

A

Nondisjunction

186
Q

Down syndrome - 3 kinds

A

Full trisomy 21

Translocation Down syndrome

Mosaic Down syndrome

187
Q

Down syndrome - Full trisomy 21

  • inheritance
  • % of down syndrome cases
  • cause
A

Not inherited

95%

Nondisjunction
(extra chromosome comes from the mother 88% of the time, and from the father 12% of the time)

188
Q

Down syndrome - Translocation Down syndrome

  • inheritance
  • % of down syndrome cases
  • cause
A

Inherited

2-3%

Balanced translocation

189
Q

Down syndrome - Mosaic Down syndrome

  • inheritance
  • % of down syndrome cases
  • cause
A

Not inherited

2-3%

Occurs as a random event during cell division early in fetal development

190
Q

Risk of Down syndrome, by maternal age:

  • 35 yrs
  • 40 yrs
  • 45 yrs
A

Maternal age 35 years - 1 in 385

Maternal age 40 years - 1 in 106

Maternal age 45 years - 1 in 30

191
Q

Recombination fraction

  • description
  • range
A

a measure of the distance between genetic loci

varies from 0% (extremely close) to 50% (on different chromosomes)

================================

  • If two loci are on different chromosomes they will segregate independently.
  • If two loci are on the same chromosome they would always segregate together were it not for the process of crossing over.
    • The nearer two loci are on a chromosome the less likely they are to be separated by crossing over.
    • The further away two loci are on a chromosome the more likely they are to be separated by crossing over.
192
Q

Gene mapping

  • essence
  • types (2)
A

Mapping the genome (i.e. establishing what every part of it does)

  • Genetic mapping - uses techniques such as pedigree analysis.
  • Physical mapping - uses molecular techniques to cut the DNA into pieces (using restriction enzymes) then to look at the pattern of pieces that result.

Physical maps can be divided into three general types:

  • chromosomal or cytogenetic maps
  • radiation hybrid (RH) maps
  • sequence maps
193
Q

Chromosomes - descriptions

  • metacentric
  • submetacentric
  • acrocentric
A

The position of the centromere divides the chromosome into two arms, the long (q), and the short (p).

  • Metacentric chromosomes - arms of roughly equal length
  • Submetacentric chromosomes - unequal arm lengths
  • Acrocentric chromosomes - very short p arms

============================
Acrocentric chromosomes can be involved in Robertsonian translocations.

194
Q

Molecular biology techniques

  • Southern blotting
  • Northern blotting
  • Western blotting
A

Southern blotting - detects DNA

Northern blotting - detects RNA

Western blotting - detects protein

==============================
SNOW (South - NOrth - West)
DROP (DNA - RNA - Protein)

195
Q

Splicing

  • description
A

takes place after transcription, prior to translation

introns are removed from an mRNA molecule, and the remaining exons are spliced together in different combinations, generating different mRNAs that are translated into distinct proteins

by this process, a single gene can code for multiple proteins

196
Q

Proteasome

  • location
  • function/process
A

protein complexes that degrade endogenous proteins (i.e. proteins manufactured by the cell).

They are located both in the nucleus and the cytoplasm.

Proteins are tagged for degradation with a small protein called ubiquitin.

197
Q

Endophenotype

  • description
  • criteria (5)
A

a heritable marker for a condition that is invisible to the naked eye and relies on some form of laboratory measurement

To qualify as an endophenotype a marker must fulfil specific criteria:

1 - It is associated with illness in the population
2 - It is heritable
3 - It is state independent (present whether or not disease is present)
4 - Within families, endophenotype and illness co-segregate (the endophenotype is more prevalent among ill relatives of ill probands than healthy ones)
5 - The endophenotype found in affected family members is found in non affected family members at a higher rate than in the general population.

198
Q

Neurofibromatosis type 1 and 2

  • inheritance pattern
A

Autosomal Dominant

199
Q

Tuberous sclerosis

  • inheritance pattern
A

Autosomal Dominant

200
Q

Achondroplasia

  • inheritance pattern
A

Autosomal Dominant

201
Q

Huntington disease

  • inheritance pattern
A

Autosomal Dominant

202
Q

Phenylketonuria

  • inheritance pattern
A

Autosomal Recessive

203
Q

Homocystinuria

  • inheritance pattern
A

Autosomal Recessive

204
Q

Hurler’s syndrome

  • inheritance pattern
A

Autosomal Recessive

205
Q

Tay-Sach’s disease

  • inheritance pattern
A

Autosomal Recessive

206
Q

Friedrich’s ataxia

  • inheritance pattern
A

Autosomal Recessive

207
Q

Wilson’s disease

  • inheritance pattern
A

Autosomal Recessive

208
Q

Cystic fibrosis

  • inheritance pattern
A

Autosomal Recessive

209
Q

Vitamin D resistant rickets

  • inheritance pattern
A

X-Linked Dominant

210
Q

Rett syndrome

  • inheritance pattern
A

X-Linked Dominant

211
Q

Cerebellar ataxia

  • inheritance pattern
A

X-Linked Recessive

212
Q

Hunter’s syndrome

  • inheritance pattern
A

X-Linked Recessive

213
Q

Lesch-Nyhan syndrome

  • inheritance pattern
A

X-Linked Recessive

214
Q

Leber’s hereditary optic neuropathy

  • inheritance pattern
A

Mitochondrial

215
Q

Kearns-Sayre syndrome

  • inheritance pattern
A

Mitochondrial

216
Q

During which phase of meiosis does genetic recombination take place?

A

Prophase I

217
Q

Schizophrenia

  • Candidate genes (4 + chromosomal locations)
A

DISC1 - chromosome 1

DTNBP1 (dysbindin) - chromosome 6 (6p 22.3)

NRG1 (neuregulin 1) - chromosome 8 (8p 21-22)

COMT - chromosome 22

218
Q

Di George (Velocardiofacial) Syndrome

  • clinical features (5)
  • chromosome affected
A

‘CATCH-22’

Cardiac abnormalities (tetralogy of Fallot)
Abnormal facies (almond-shaped eyes, low-set ears)
Thymic aplasia (hence recurrent infections)
Cleft palate
Hypocalcemia/Hypoparathyroidism (causing short stature and seizures)
2
2

219
Q

Heterogeneity

  • essence
A

refers to the presence of a variety of genetic defects which cause the same disease.

220
Q

Frontotemporal dementia

  • candidate genes (2)
A

PGRN (progranulin)

MAPT (tau)

221
Q

Huntington’s disease

  • candidate genes (1)
A

IT15 (huntingtin)

222
Q

CADASIL
(cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy)

  • candidate genes (1)
A

Notch3 (notch 3)

MRCPsych Part A small (6 decks)

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