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TAS Revision > Genetics > Flashcards

Genetics Flashcards

1
Q

What is chorionic villus sampling?

A

Sampling of the placenta
Occurs during the first trimester (usually weeks 10-13)
Relative risk of miscarriage is 1.5-2%

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2
Q

What is amniocentesis?

A

Sampling of the amniotic fluid which contain cells shed from the foetus skin
Usually occurs between weeks 16-18

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3
Q

Which inheritance pattern is not transmitted by males?

A

Mitochondrial Inheritance

Males do not transmit mitochondrial disorders because mitochondrial DNA is always exclusively maternally inherited. Paternal mDNA is eliminated from the egg in the early stages of embryogenesis

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4
Q

Which trinucleotide repeat relates to Fragile X?

A

CGG

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5
Q

Which trinucleotide repeat relates to Friedrichs Ataxia?

A

GAA

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6
Q

Which trinucleotide repeat relates to myotonic dystrophy?

A

CTG

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7
Q

Which trinucleotide repeat relates to spinocerebellar ataxia?

A

CAG

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8
Q

What are the main features of Fragile X?

A

Results from a loss of function mutation of FMR1 gene
Inherited in X-linked dominant fashion
Commonest cause of intellectual disability
Other features include - macroorchidism, large ears, high forehead, mitral valve prolapse and otitis media

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9
Q

Commonest cardiac problem in Noonan’s syndrome?

A

Pulmonary Valve Stenosis

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10
Q

Which genes are affected in Noonan’s syndrome?

A

Autosomal dominant inheritance
Mutation of PTPN11 gene on chromosome 12
Mutation of SOS1 gene on chromosome 2

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11
Q

How does William’s syndrome tend to present?

A

Over friendly personality
Supravalvular aortic stenosis
Facial features - thick everted lips, widely spaced teeth, upturned nose

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12
Q

Which genes are affected in Williams syndrome?

A

Microdeletion on 7q which encompasses for elastin gene

Hence testing for chromosome microarray will detect this

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13
Q

What are the features of DiGeorge Syndrome?

A

Microdeletion of chromosome 22q11.2
Features include:
Chromosome 22
Abnormal facies
Thymic aplasia
Cleft palate
Hypocalcaemia/ hypoparathyroidism

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14
Q

What are the features of Prader-Willi syndrome?

A

Causes include:
- Microdeletion of paternal chromosome 15q11.2-q13
- Maternal uniparentalidosomy of chromosome 15
- Imprinting defect

Features include:
- Compulsive over-eating
- Temper tantrums
- Mild intellectual disability

Diagnosis is by methylation studies

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15
Q

Outline which factors are affected in haemophilia?

A

Haemophilia A - factor VIII
Haemophilia B - factor IX

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16
Q

Which conditions represent maternal and paternal uniparental disomy of chromosome 15?

A

Maternal uniparental disomy of chromosome 15 - Prader Willi Syndrome
Paternal uniparental disomy of chromosome 15 - Angelmann Syndrome

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17
Q

What are the features of Duchenne’s Muscular Dystrophy?

A

X-linked recessive disorder
60% have the exon deletion or duplication of the dystrophin gene
All muscle affected - including cardiac
Typically die age 20-30 of cardiomyopathy
Deflazacort and prednisolone improve motor function - Deflazacort can cause increased risk of cataracts
Signs include calf hypertrophy and positive Gower’s sign (inability to get up from standing without use of hands)

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18
Q

What are the features of Edward Syndrome?

A

Intellectual disability
Microcephaly
Low set ears
Rocker bottom feet
Overlapping fingers
VSD

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19
Q

What are the features of Patau Syndrome?

A

Polydactyly (postaxial - on the ulnar side)
Cleft Palate
Microcephaly
Cutis Aplasia - area of baldness
PDA or VSD

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20
Q

What is trisomy 18?

A

Edward Syndrome

21
Q

What is trisomy 13?

A

Patau Syndrome

22
Q

What is 47, XXY?

A

Klinefelters Syndrome

23
Q

What are the features of Klinefelters Syndrome?

A

Tall
Gynaecomastia
Hypogonadism (small, firm testes)

Increased risk of breast cancer and testicular germ cell tumours

24
Q

What are the laboratory findings in Klinefleters Syndrome?

A

High LH and FSH
High estradiol
Low serum testosterone

25
Q

What is the treatment of Klinefelters syndrome?

A

Treatment with testosterone around the time of puberty (12 years old)

26
Q

What is the treatment in Turners Syndrome?

A

Growth hormone
Eostrogen treatment at puberty
HTN treatment
Thyroid replacement if required

27
Q

What are the features of Noonan’s syndrome?

A

Intellectual disability (25%)
Bleeding disorders
Pulmonary Valvular stenosis
Small penis
Cryptorchidism

Features similar to Turners syndrome such as short stature, cubits values and short webbed neck

28
Q

How is William’s syndrome diagnosed?

A

FISH for the 7q11.23 elastin gene deletion

29
Q

What are the features of William’s syndrome?

A

Failure to thrive
Hypotonia
SUPRAVALVULAR AORTIC STENOSIS
Cocktail party personality
Stellate pattern of the iris
Sensorineural hearing loss

30
Q

What is WAGR syndrome?

A

Wilm’s tumour (50% of cases) - haematuria, abdominal mass
Aniridia
Genitourinary Anomalies (hypospadias, cryptorchidism, gonadoblastoma)
Retardation + intellectual disability

31
Q

What genes are affected in Alagille syndrome?

A

Microdeletion of the 20p12 gene - JAG1 gene mutation

32
Q

What are the features of Alagille syndrome?

A

Broadened forehead + pointed chin
Jaundice (cholestasis due to bile duct paucity)
Cardiac - peripheral pulmonary stenosis (systolic murmur) + ToF
Butterfly hemivertebrae

33
Q

How do you diagnose DiGeorge syndrome?

A

Array comparative genomic hybridisation - gold standard
FISH - widely available and more affordable but can miss the diagnosis as it is a micro deletion

34
Q

What are the features of cri-du-chat syndrome?

A

Moon face
Flat nasal bridge
Down-slanting palpebral fissures
Microcephaly
Strabismus
Hypotonia -> poor feeding
High pitched cry

35
Q

What is the mutation causing cri-du-chat syndrome?

A

Deletion of 5p

36
Q

What is the mutation causing achondroplasia?

A

Mutation in the gene for fibroblast growth factor receptor 3 (FGFR3) on chromosome 4

Autosomal dominant

37
Q

What is the mutation causing Marfans syndrome?

A

Defect in FBN1 gene on chromosome 15q; fibrillin

Autosomal dominant

38
Q

What are the features of Marfan’s Syndrome?

A

Dislocated lens
Aortic dissection/ rupture of the aorta
Scoliosis
Long arms/ fingers
Pectus excavatum (funnel chest)
Pectus carinatum (pigeon breast)
Tall and thin

39
Q

What the diagnostic criteria make up the “Revised Ghent Criteria” used to diagnose Marfan syndrome?

A

Family History
Aortic root dilatation
Ectopia Lentísimas
Systemic Score Points
Identified FBN1 mutation

40
Q

What mutations cause Ehlers-Danlos Syndrome?

A

Mutation of COL5A1 or COL5A2 genes (Collagen type 5 genes)

41
Q

What mutations occur in Beckwith-Wiedemann Syndrome?

A

Abnormalities of the distal 11p->IGF2

(Over production of insulin like growth factor 2 which causes overgrowth of organs)

42
Q

What are the features of Beckwith-Wiedemann Syndrome?

A

Neonatal period:
- Severe hypoglycaemia
- Omphalocele
- Umbilical hernia
- Large tongue (macroglossia)

Hemi-hypertrophy
Pits of the external ear
High risk of development of Wilm’s tumour (patients should have abdominal USS every 3 months until 3 years then every 6 months)

43
Q

What is Klipple-Feil syndrome?

A

Due to a defect in formation of the segmentation of cervical vertebrae

Features include:
- Short neck or webbed neck
- Low hairline
- Associated with single kidney

44
Q

What are the features of Treacher-Collins Syndrome?

A

Affects facial bones, ears and eyes

Underdeveloped mandibular and zygomatic bones
Conductive hearing loss
Coloboma
Aplasia of the lid lashes

45
Q

What are the features of Waardenburg Syndrome?

A

Hair hypo pigmentation + premature greying of hair
Abnormal pigmentation of the iris (both eyes can be different colours - heterocromia)
Associated with hirschsprungs disease

46
Q

What are the clinical features of Turner’s Syndrome?

A

Webbed neck/ cystic hygroma
BICUSPID AORTIC VALVE
Short stature
Wide carrying angle
Short 4th and 5th metacarpal/tarsal
Wide spaced nipples
Horseshoe kidneys
Lymphoedema at birth - resolves after several months

46
Q

Which pharyngeal arches are affected in DiGeorge Syndrome?

A

Third and Fourth

47
Q

What type of mutations is FISH genetic testing specifically used for?

A

Microdeletions

NB: rare very small deletions may not be detected on FISH testing - use microarray testing in these cases

48
Q

How does FISH testing work?

A

Detects a specific DNA sequence on a chromosome

DNA probe containing a fluorescent probe detects specific chromosome - 2 signals is normal, 1 signal means a deletion

TAS Revision (14 decks)

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