Molecular genetics

Question 1

What steps of the cell cycle constitute interphase

Answer 1

All except mitosis i.e. G0, G1, S & G2

In interphase the genetic material and organelles of the cell duplicate

The chromatids (half of chromosome that we get from each parent) duplicate and are joined together at nucleus:
- 46 chromosomes become 92 chromatids

Question 2

Outline the stages of mitosis

Answer 2

Prophase:
- Chromatids condense
- Spindle fibres form

Metaphase:
- Nucleus breaks down
- Spindle fibres attach to each chromatid and they line up at equator of cell (metaphase plate)

Anaphase:
- The chromosomes separate into chromatids through the shortening of spindle fibres dividing the centromeres
- Aligned at opposites of the cells

Telophase:
- New nuclear membrane forms around each set of chromosomes
- Spindle fibres split down
- Cytokinesis - the cell membrane splits via pinching into two separate cells separating each set of chromatids

Question 3

Outline the stages of mitosis

Answer 3

Prophase:

Metaphase

Anaphase

Telophase

Question 4

How does meisosis differ to mitosis?

Answer 4

In mitosis cells divide to form two daughter cells each with same amount of chromosomes as the parent (46)

In meiosis cells divide to form 4 daughter cells with half the amount of chromosomes as the parent (23):
- The process involves the same prophase, metaphase, telophase and cytokinesis however this happens twice
- The first time round in interphase rather than chromatids duplicating and attaching at centromeres whole new chromosomes are produced
- Therefore in the first metaphase M1 these line up side by side –> when anaphase splits them and telophase forms a ring around the new cells each has the same amount of DNA as at the start
- A seconds P2,M2, T2 and cytokinesis then occurs dividing the genetic material by half

Question 5

What is crossing over?

Answer 5

Occurs in prophase 1 of meisosis - ends of sister chromosomes may overlap at similar genes positions sharing DNA to form recombinant chromosomes

Question 6

What do the numbers 1, 2, 3 , 4 represent

Answer 6

1 - telomere
2 - centromere
3 - p i.e. short arm of chromosome
4 - q i.e. long arm of chromosome

Question 7

What is a metacentric vs acrocentric/submetacentric chromosome?

Answer 7

Metacentric chromosome - centromere is at the centre (i.e p and q arms are equal length)
Acrocentric/submetacentric - centromere is at one end

Other types of chromosome (telocentric and holocentric) are not seen in humans

Question 8

What name is given to cells with the incorrect number of chromosomes?

Answer 8

Aneuploid cells

• Aneuploidy can occur from extra number or one chromosome (trisomy 21 for example) or rarely if total chromosome number multiples (triploidy or tetraploidy) however the later to cause spontaneous abortion

Question 9

How does trisomy/monosomies arises?

Answer 9

From non-disjunction during meisosis - a failure of the chromatids/chromosomes to separate

This can lead to one gamete having double the sets of one chromosome than it should - produces trisomy OR the gamete may have no set of one chromosome - produces monosomy

Moasiacism occurs when the non-disjunction occurs in mitosis after the gametes fuse - this causes the production of two cell lineages (with and without trisomy) leading to milder symptoms

Only trisomy 21 survives into adulthood, trisomies 13 and 18 often die in childhood

Question 10

What are the genetic abnormalities of

a) Downs syndrome
b) Turners syndrome
c) Pataus syndrome
d) Edwards syndrome
e) Metafemale

Answer 10

a) Trisomy 21

b) Turner’s syndrome - single X chromosome 45X

c) Trisomy 13

d) Trisomy 18

e) Trisomy X chromosome

Question 11

What are the gestational signs of down’s?

Answer 11

Reduced alpha feto protein
Increased bHCG
A single nuchal fold on USS

Question 12

Outline some clinical signs of downsyndrome?

Answer 12

Prominent epicanthal folds
Single palmar crease
Low set ears
Intellectual disability
Hypothyroidism
Heart abnormalities (ASD)

Question 13

How does Edward’s syndrome present?

Answer 13

More common in girls > boys

Rocker bottom feet
Low set ears
Severe intellectual disability
Small jaw (microganthia)
Congenital heart disease
Clenched hands
Prominent occiput
Widely spaced eyes
Overlapping fingers

Question 14

How does Patau’s syndrome present?

Answer 14

Microcephaly
Microphthalmia
Cleft lip/palate
Polydactyly
Colomba eye
Intellectual disability
Abnormal forebrain structure

Question 15

How does Turner’s syndrome present?

Answer 15

Short stature
Webbed neck
Low hairline
Retrognathism (posterior position of mandible)

Disharmonic IQ profile - normal verbal, reduced performance.

Usually only X is maternal in origin (80%) if paternal then better IQ.
This differs to other syndromes described where often aneuploidy arises in the maternal gamete

Question 16

What is a nucleoside?

Answer 16

A molecule made of a nitrogenous base and a pentose sugar - when phosphorylated they are nucleotides - the components of nucleic acid

Question 17

What is DNA made of?

Answer 17

Deoxyribose-phosphate backbone and bases of nucleic acid - two stands joined together by hydrogen bonds

Bases can be purines (Adenosine or Guanine) or pyrimidine (Thymine or Cystosine)

Question 18

How many base pairs make a codon?

Answer 18

3 - each codon indicates a specific amino acid. There are 20 amino acids. 10 are essential and are not derived from food but need to be synthesised within the body

Question 19

What are protein coding regions

Question 20

Name two type of introns sequences

Answer 20

Interspersed:
- Long interspersed
- Short interspersed

TANDEM REPEATs:

Satelite:
- Large series of repeats

Microsatelite - telomeric repeats (chromosomal integrity)
- hypervariable repeats (DNA finger-printing)

Minisatelite - single, di or trinucleotide repeats

Question 21

What does hnRNA refer to?

Question 22

What does hnRNA refer to?

Answer 22

Heterogenous nuclear RNA - RNA that contains non codon regions (introns)

Splicing is the process that removes these regions resulting in messenger RNA that leaves the nucleus

Question 23

What do nucleosomes do?

Answer 23

Nucleosomes remove non-coding RNA from hnRNA to produce mRNA

Question 24

Where are ribosomes found?

Answer 24

In the cytoplasm attached to rough endoplasmic reticulum

Question 25

Name the 3 stages of translation

Answer 25

Initiation - methionine containing tRNA binds to the polpeptide P site of the Ribosome Elongation - at the aminoacyl A site each new tRNA binds (with attached amino acids bind). Amino acids are bound 1 by 1 Termination - termination sequence UAG, UAA or UGA signals end of protein Modification is extra post translation changes that occur to the protein before it becomes functionally active. This occurs in the ER or golgi bodies - it can occur spontaneously as translation occurs

Question 26

What is aminoacyl-tRNA synthetase?

Answer 26

The enzyme that binds tRNA to specific amino acids in the presence of Mg2+

Question 27

What is translocation

Answer 27

A reciprocal exchange of genetic material between 2 chromosomes In Robertsonian translocation exchange is not reciprocal and from 2 chromosomes the p arms are lost and one metacentric chromosome is formed. i.e from one 14 and one 21 - produces 14/21 (alongside remaining 14 and remaining 21) - When meisosis gametes formed can contain 14/21 and 21 --> produce trisomy 21 during fertilisation - OR gamete may only have one 14 or 21 --> monosomy 14 or monosomy 21 Robertsonian translocation accounts for 4% of downs Robertsonian translocation chromosome can be inherited from either parent

Question 28

Outline the genetic abnormalities and brief symptoms associated with a) DiGeorge (Velocardiofacial) b) William Syndrome c) Smith Magnesis Syndrome d) Angelmann Syndrome e) Prader Willi f) Cru-di-Chat

Answer 28

a) 22q.11.2 autosomal dominant - 25% get psychosis, mild to moderate LD, facial deformity including cleft palate, absent or malformed parathyroid (hypocalcaemia), articulatory problems, broad nasal bridge b) 7.11 microdeletion - hypercalcium, supravalvular aortic stenosis, speech superficially fluent, mild-moderate LD, disinhibited, hyperacusis c) 17.11.2 microdeletion - mild-moderate self-harm, pulling off nails, sleep disturbances and hugging, inserting of foreign objects, moderate to severe LD d) 15q11-13 maternal deletion - developmental delay, low IQ, jerking movements and hand flapping e) 15q11-13 deletion - obesity, small stature, decreased IQ, skin picking, hyperphagia - small gonads f) 5p chromosome deletion (locus 5p.15.2) - small facial features (poorly developed), cat-like cry, feeding difficulties

Question 29

Name the 3 mendelian laws

Answer 29

Law of uniformity - the offspring must inherent either trait from each parent Principle of segregation - only one allele from each parent passes to the child and is from pure chance - the parental alleles separates during meiosis. Thus if A and B alleles with Mother AB and Father AB child can be AA, BB or AB Independent assortment - different traits do not depend on each other

Question 30

Outline how the risk of Schizophrenia varies in the following a) General population b) First cousin c) Aunt/Uncle d) Niece/nephew e) Grandchildren f) Parent g) Half sibling h) Full sibling i) Children j) Fraternal twins (non-identical) k) Off spring of parents with Schz l) Identical twins

Answer 30

a) General population 1% b) First cousin 2% c) Aunt/Uncle 2% d) Niece/nephew 4% e) Grandchildren 5% f) Parent 6% g) Half sibling 6% h) Full sibling 9% i) Children 13% j) Fraternal twins (non-identical) 17% k) Off spring of parents with Schz 46% l) Identical twins 48%

Question 31

If there is a mutation affecting the transcriptional activity of a new gene it is likely to affect?

Answer 31

The promoter region of the gene - the area of DNA that RNA polymerase binds to in order to begin mRNA synthesis from DNA

Question 32

What are the 5 conditions that need to be met to ensure Hardy-Weinberg Equilibrium

Answer 32

a) No mutations b) No loss or gain of genetic info c) Random mating d) Population is large enough to ensure no genetic drift - i.e. random chance of geneotype or allelic frequency changing e) No natural selection - i.e. a genotype or allele cannot confer a survival advantage

Question 33

What is the Hardy-Weinberg Equation

Answer 33

p2 + 2pq + q2 = 1 p2 (autosomal dominant) 2pq (heterozygous) q2 (autosomal recessive)

Question 34

What type of analysis determines the method of inheritance using family data?

Answer 34

Segregation analysis

Question 35

What is linkage analysis

Answer 35

A method that identifies a piece of DNA of known location that is present in affected individuals (inherited) but not unaffected individuals - from here the disease gene must be close

Question 36

Lyonisation is the process where...

Answer 36

One of the X chromosomes is made inactivated to prevent a toxic double dose of x-linked genes. The x-chromosome made inactive is called a Barr body

Question 37

This condition results in multiple non-malignant tumours growing in the brain and body of an individual?

Answer 37

Tuberous sclerosis - implicated genes are TSC1 and TSC2 Psychiatric co-morbidities include Autism, ADHD, Anxiety and Psychosis Seizures, developmental delay and skin lesions It is autosomal dominant with variable expression but 95% penetrance

Question 38

Name some diseases with mitochondrial inheritance

Answer 38

Leber's hereditary optic neuropathy Kearn's Sayre syndrome

Question 39

Name an anagram to remember DiGeorge Syndrome

Answer 39

Cardiac abnormalites Abnormal faces Thymic aplasia - recurrent infections Cleft palate Hypocalcaemia/Hypercalcaemia 2 2

Question 40

What are the trinucleotide repeats seen in a) Huntington's b) Fragile X syndrome c) Muscular dystrophy d) Friedrich's ataxia

Answer 40

a) CAG b) CGG c) CTT d) gAA

Question 41

What are the symptoms of fragile X syndrome and what gene is affected?

Answer 41

Affects FMR1 gene - CGG repeats at exon sites (FRAXA, FRAXE, FRAXF) If > 52 repeats - destablisation during spermatogenesis or oocytogenesis and expansion occurs Clinical symptoms if > 200 repeats: - Men - large testes, lower IQ, prominent ear lobes, high pitch voice and mental retardation - Women -> mild LD, early menopause If 55-200 then premutation: - Men --> intention tremor and ataxia later in life - Women --> premature ovarian failure and cognitive/behavioural difficulties - Shows anticipation

Question 42

What chromosome is Huntington's expressed on?

Answer 42

Chromosome 4 - 4p16.3 - a trinucleotide repeat of CAG here (40-55) Unlike x-linked diseases here if paternal mutation inherited - there is greater repeats and anticipation (in x-linked diseases tends to be if maternal gene then greater anticipation)

Question 43

What mechanism is responsible for genomic imprinting?

Answer 43

DNA methylation Parent of origin phenomenon - i.e. where it matters if gene inherited from mother or dad which syndrome occurs Prader Willi 15q11-13 - paternally inherited (20% of cases come from maternal uniparental disomy - i.e. both copies from mum) Angelman Syndrome 15q11-13 matrernally inherited (only 4% of cases are from paternal uniparental disomy)

Question 44

Outline how the following disorders are inherited and briefly their symptoms: a) Tuberous Sclerosis b) Treacher Collins Syndrome c) Apert syndrome d) Noonan syndrome e) Hurler syndrome f) Lesch-Nyan syndrome

Answer 44

a) Auto Dominant but most spontaneous 9q34/16p13 - Ash leaf macules, brain hamartomas, mental retardation, adenoma sebaceum, heart and kidney cysts b) Auto dominant 5q31 - down slanting eyebrows, maxo/mandibular hypoplasia, malformed pinna, moderate LD c) Auto dominant 10q - craniosynostosis (fusing of skull), mitten hands, trapezoid mouth, variable LD d) Autosomal dominant - Chr 12 - LD, cryptorchidism, pulmonary stenosis, webbed neck, short stature e) Autosomal recessive 4p16 - corneal oedema, deteriorating IQ after age 2, joint stiffness and coarse features f) Xq26-27. X-linked recessive - affects enzyme HGPRT. Presents with poor muscle control, self-mutilating behaviours, gout (hyperuricaemia and hyperuricosuria). Can present at any time

Question 45

What prevalence do polymorphisms need to occur in a population?

Answer 45

At least 1% They must occur with normal but varied presentation (i.e. not disease causing)

Question 46

Outline different types of polymorphism?

Answer 46

Single nucleotide polymorphisms Variable tandem repeat polymorphisms: - Short tandem repeat polymorphism - microsatellites (2-6 bases) - Minisatellites 20-70 bases Restriction fragment length polymorphisms - these variations change the site that restriction enzymes act on DNA Length polymorphisms

Question 47

What is the founder effect?

Answer 47

Loss of genetic variation that occurs when a new population is established from few members - acts to maintain polymorphisms - alongside genetic drift and natural selection

Question 48

How do Southern, Western and Northern blotting vary?

Answer 48

Southern - detection of specific DNA sequence after electrophoresis Western - detection of specific protein after electrophoresis Northern - detection of specific RNA after electrophoresis

Question 49

How many steps does PCR have

Answer 49

3 1. DNA is denatured into single strand - then cooled to anneal and primers bind 2. DNA polymerase binds to extend length 3. Cycling repeats to get necessary amounts

Question 50

What bacteria does DNA cloning use?

Answer 50

Plasmids

Question 51

Define heritability

Answer 51

The proportion of variation in a trait (polygenic & quantitative) that is explained by genetic factors Narrow-sense heritability refers to the variation that is explained by additive gene effects Broad-sense heritability refers to the variation in phenotype that is explained by (additive + non-additive gene effects). Non-additive gene effects = epistasis (gene - gene interactions) or dominance (presence of one gene mitigates the effect of another).

Question 52

What genes affect inheritance of Alzheimer's?

Answer 52

APOE located on chromosome 19 - affects the breakdown of bAmyloid plaques: - APOE1 protective - APOE3 neutral - APOE4 increased risk (15-30 x if homozygous vs. 3 x if heterozygous) APP gene - codes for production of APP. Located on chromosome 21 - may account for Alzheimer's in down's syndrome PENS1 - Presenelin 1 - chromosome 14 PENS2 -Presenelin 2 - chromosome 1. These genes code for enzymes that cleave APP - when cleaved abnormally insoluble and becomes Alzheimer's. Early onset Alzheimers - most genetic influence PENS1 (30-70%), then APP (10-15%) then PENS2 (5%)

Question 53

How does most aneuploidy come from?

Answer 53

Non-disjunction of during meiosis 1 - most aneuploidy in humans is from trisomy's

Question 54

Name some candidate genes for Schizophrenia

Answer 54

DTNBP1 (dysbindin) - chromosome 6 (6p 22.3): decreased in Schz relates to lower glutamate levels (lyosome related organelles) COMT - chromosome 22: involved in the breakdown of Dopamine. Low activity levels linked to Schz and OCD NRG1(neuregulin 1) - chromosome 8 (8p 21-22): growth factor involved in neuron differentiation. High NRG1 level may suppress NMDA receptor and lower glutamate signalling. G72 - chromosome 13 RGS4 - chromosome 1 DAOA - chromosome 13 DISC1 - chromosome 1: multifactorial protein involved in neuron development DRD2 - chromosome 11

Question 55

Name some genes linked with dyslexia

Answer 55

DCD2 GCFC2 ROBO1 MRPL19 DXY1C1 KIAA0319

Question 56

What is the exam heritability estimates for Sch and BD

Answer 56

50-60%

Question 57

What mode of inheritance is CADASIL?

Answer 57

Autosomal dominant - associated gene is Notch3

Question 58

Where do CAG repeats happen on Huntington's?

Answer 58

Chromosome 4

Question 59

What is the prevalence of caucasian individuals homozygous for ADH1B*1?

Answer 59

85-95% ADH1B*1 codes for slow metabolism of alcohol to acetaldehyde (unpleasant intermediate that codes for dizziness, nausea and tachycardia) There are two other loci at similar positions to ADH1B on 4q2123 - ADH1A and ADH1B. ADH1C*1 and ADH1B*2 alleles code for fast metabolism of alcohol ADH4 has been associated with early onset of drinking DRD2 (A1 allele) has also been associated with risk factor for alcohol dependence

Question 60

Apart from ADH1B what other genes have been linked to alcohol use disorder?

Answer 60

ALDH2 - these genes code for aldehyde dehydrogenase that converts acetaldehyde to acetate ALDH2*504K codes for Asian flush due to fast metabolism of alcohol (tachycardia, facial flushing, nausea) and this is protective for alcohol dependence Other alleles ALDH2*1 and ALDH2*2 are present in 50% of Asian populations and absent outside of Asia

Question 61

What is the risk of Schz in MZ and DZ twins?

Answer 61

MZ - 50-60% DZ - 28% Risk increases if hebephrenic schizophrenia (disorganised) In Schz symptom severity may not associate greatly to familial risk however age of onset may do

Question 62

Outline the heritability estimates for BD and the risk in the general population, 1st degree relative and MZ twin

Answer 62

Heritability 85-90% General population 0.5-1.5% First degree relative (RR 8) 10-15% MZ twin (40-70%) Risk of unipolar depression if have a relative with BD - First degree relative 10-20% - MZ twin 15-25% general population (5-10%)

Question 63

Name some genes associated with bipolar disorder?

Answer 63

BDNF 11p13 DAO G72/G30 13q33 COMT 22q11 - low activity may associate to rapid cycling

Question 64

Outline risk of depression in individuals with a first degree relative, MZ twin, DZ twin

Answer 64

1st degree 5-30% MZ - 40% DZ 11% Heritability is 20-80%

Question 65

Name some genes associated with FTLD

Answer 65

All of below are autosomal dominant: MAPT (microtubule) associated protein tau gene) 17q21 Or Progranulin 17q21 --> particularly tau negative changes. Progranulin inolved in wound repai, infammation and tumorigenesis C9orf72 - chromosome 9 (accounts for 20-50% of genetic cases)

Question 66

Name some of the Parkinson associated genes?

Answer 66

PARK1, PARK4 - dominant - onset in 40a with lewy bodies - gene of alpha synuclein 4q21 PARK 2 - recessive - most common early onset (40-60s), Nigral degeneration without Lewy bodies. Parkin affecting, 6q25. L-DOPA responsive PARK 8 - dominant - 12 cen pericentromeric LRRK2 gene. Onset in 60s some alpha synuclein and tau PARK 6 - recessive - earliest onset 30-40s, L-DOPA responsive. 1p35-37 PTEN-INduced Kinase (PINK1) in mitochondria PARK 7 - recessive - autosomal recessive 30-40s onset 1p38 DJ-1

Question 67

What is the heritability of Autism?

Answer 67

90% 1st sibling risk 2-8% (50x RR) If 2 siblings with autism (300x RR) MZ risk is 60-92% DZ risk is 0

Question 68

What is the heritability of Autism?

Answer 68

90% 1st sibling risk 2-8% (50x RR) If 2 siblings with autism (300x RR) MZ risk is 60-92% DZ risk is 0-30% Chromosomes 2, 7 and 15 have been implicated

Question 69

Where is the Huntington's gene (HTT) found

Answer 69

On chromosome 4 - autosomal dominant

Question 70

Name a gene associated with DLB?

Answer 70

SNCA - located on chromosome 4 GBA (on chromosome 1) or APoE (on chromosome 19) are associated with increased risk

Question 71

What is Wolf-Hirschorrn syndrome

Answer 71

Syndrome where children get a "greek warrior helmet appearance" to their head with broad flat nose and high forehead. At risk of recurrent seizures as a child - associated with deletion at short arm (p) of chromosome 4

Question 72

What does knights move inheritance pattern refer to?

Answer 72

X-linked recessive

Question 73

What is the inheritance of Kleinfelter's?

Answer 73

Sporadic

Question 74

In X-linked dominant how does inheritance follow?

Answer 74

No male to male transmission All daughters from affected males are cases

Question 75

What is the risk of developing late stage Alzheimer's if homozygous for APOE4?

Answer 75

10-30%

Question 76

What stage of the cell cycle does DNA replication take place?

Answer 76

Synthesis stage

Question 77

Where is the mutation seen on Smith Magnesis syndrome?

Answer 77

17p

Question 78

Where does the deletion happen on Cru Di Chat

Answer 78

Terminal end of chromosome 5

Question 79

What type of mutation is most commonly seen in Beta Thalassaemia

Answer 79

Non-sense mutation in beta-globulin gene that results in reduced/absent HBB gene expression As autosomal recessive - homozygotes present with severe haemolytic anaemia due to absent HbA production. Beta-thalassaemia minor the trait condition

Question 80

Does Tuner's syndrome present with intellectual diasbility?

Answer 80

Rarely - often IQ comparable to generaly population, sometimes there is visuospatial learning deficits Results from monosomy of X (45 XO) in females

Question 81

What is DiGeorge syndrome also known as and how does it present?

Answer 81

Velo-cardiofacial syndrome - Fish (mouth) - Pharyngeal insufficiency - Severe LD - Supra-valvular aortic stenosis - Hypocalcaemia - Hypospadias - Long thin hands - Microcephaly - Cleft palate - Small mouth - Long face - Prominent tubular nose

Question 82

How do MZ and DZ twins arise?

Answer 82

MZ twins occur when the embryo is cleaved in early childhood: - Here two genetically identical embryos are made - 70% of these share the same chorion and therefore have a more similar uterine environment than females DZ twins are the result of two sperm fertilising one ovum: - Share 50% of their genes - Always have their own chorion

Question 83

If there is a strong family history what is the risk of the child developing alcohol dependence?

Answer 83

4-6 x more likely

Question 84

The locus of the COMT gene is?

Answer 84

22q11 - note site of DiGeorge microdeletion ?explains the increased risk of Schz 22q11.2

Question 85

Outline the broad criteria for polymorphisms

Answer 85

Occur in a rate of 1% or above in general population They are maintained by evolutionary processes Do not result in functional deficits - they associate with a normal phenotype

Question 86

What is Kisspeptin 1 and what condition has it been linked to?

Answer 86

Kisspeptin 1 - KISS1 has been linked to Kallman's syndrome (delayed or absent pubertal onset and loss of sense of smell)

Question 87

For Huntington's disease which parent does the gene need to be inherited through to exhibit more a unstable presentation?

Answer 87

Through the father - male germline tends to exhibit earlier presentation Neuropathy results from intranuclear inclusions of the HTT protein

Question 88

What is alternative splicing?

Answer 88

Splicing together of exons in different combinations thus to make different proteins out of one gene

Question 89

Which condition has a deficiency of phenylalanine hydroxylase?

Answer 89

Phenylktonuria (PKU) - autosomal recessive and leads to build up of phenylalanine in the body which can cause severe mental disability. It can't be cured but can be managed through reducing levels of phenylalanine in the diet

Question 90

What does aminoacyl synthetase do?

Answer 90

Aminoacyl synthetase adds the correct amino acid to the tRNA - this is called aminoacylation

Question 91

Name some symptoms of Rett's syndrome?

Answer 91

Intellectual disability Stereotypical hand movements around the midline Grimacing Teeth grinding Ataxia Loss of speech It is x-linked recessive and predominantly affects girls

Question 92

What is a nucleoside?

Answer 92

A nitrogenous base (DNA base) and a pentose sugar - when this is phosphorylated it becomes a nucleotide DNA is made up of nucleotides with a deoxyribose sugar backbone

Question 93

When is the Hardy-Weinberg Equation used?

Answer 93

Only to work out the frequency of heterozygotes for carriers of a autosomal recessive condition p2 + 2pq + q2 = 1 p2 is the frequency of autosomal dominant homozygotes (USUALLY 1) 2pq is the frequency of heterozygotes q2 is the frequency of autosomal recessive homozygotes Therefore to the risk of heterozygotes is twice that of frequency of autosomal recessive homozygotes - 2 x (1) x q

Question 94

In Turners syndrome (45X0) where does the x-chromosome usually come from?

Answer 94

The mother in 80% This is as paternal error of meiosis often causes the x-not to be transmitted

Question 95

What genes have been linked with autism?

Answer 95

SHANK1, SHANK2, SHANK3 - codes for SH3 and multiple ankyrin repeat proteins involved in scaffolding present at Glutamatergic synapses in the CNS

Question 96

What can detect the presence of trinucleotide repeats?

Answer 96

PCR

Question 97

How to proteasomes know what endogenous cellular components to degrade?

Answer 97

They are labelled with Ubiquitin

Question 97

How to proteasomes know what endogenous cellular components to degrade?

Answer 97

They are labelled with Ubiquitin

Question 98

What mode of inheritance is CF?

Answer 98

Autosomal recessive

Question 99

What is the heritability of ADHD

Answer 99

74% - similar between males and females More due to genetic > environmental factors 2/3 have ADHD symptoms into adulthood Candidate genes include: DAT1, DRD4, DRD5, 5HTT, HTR1B, and SNAP25.

Question 100

How does Williams syndrome present?

Answer 100

Elfin like features, social disinhibition, sensitive hearing, advanced verbal skills but superficial speech (cocktail party speech), can also get hypercalcaemia and endocrine problems 7q11 deletion - most are sporadic Can be autosomal dominant if inherited

Question 101

If there is profound LD, seizures, sleep problems, ataxia, flexed arms when walking (flapping hand movements) what condition may you suspect?

Answer 101

Angelman syndrome Caused from maternal origin 15q11

Question 102

What is a haplotype?

Answer 102

A set of genetic variations that gets inherited together A karyotype is an individuals complete set of chromosomes A genotype is an individuals complete set of genes

Question 103

Name some x-linked recessive inherited conditions?

Answer 103

Cerebellar ataxia Hunter's syndrome Lesh-Nyan syndrome

Question 104

As a phenotype is the observable traits what does it reflect?

Answer 104

The interaction between genetic and environmental factors

Question 105

As a phenotype is the observable traits what does it reflect?

Answer 105

The interaction between genetic and environmental factors

Question 106

What are the broad names for alcohol associated enzymes?

Answer 106

Alcohol dehydrogenase Aledhyde dehydrogenase

Question 107

What is the HTT gene also referred to as?

Answer 107

IT15 on chromosome 4

Question 108

What are the DNA stop codons?

Answer 108

TAA, TAG TGA

Question 109

All of these conditions (Phenylketonuria, homocystinuria, Hurler's syndrome, galactosaemia, Tay-Sach's disease, Friedrich's ataxia, Wilson's disease, cystic fibrosis ) have what mode of inheritance?

Answer 109

Autosomal recessive

Question 110

How is tuberous sclerosis?

Answer 110

Most are sporadic mutations (3/4) otherwise it is inherited in an autosomal dominant fashion

Question 111

What is small interfering RNA?

Answer 111

Double stranded RNA molecule that can disrupt the expression of a gene