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mrcog part 1 > Revision notes: 1. Genetics > Flashcards

Revision notes: 1. Genetics Flashcards

1
Q

DNA replication. Which enzyme unwinds double-stranded DNA

A

DNA helicase

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2
Q

Which enzyme is involved in copying DNA during replication

A

DNA polymerase

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3
Q

Which enzyme is involved with reattaching DNA strands

A

DNA ligase

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4
Q

4 stages of the cell cycle

A

G1 –> S (synthesis) –> G2 –> M (mitosis

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5
Q

Stages of mitosis

A

Prophase - Chromatins condense

Metaphase - Nuclei disappear, nuclear membrane disintegration, mitotic spindles form and chromosomes align at metaphase plate

Anaphase - ‘kinetochore’ microtubules shorten, splitting the chromatids

Telophase - chromosomes decondense, nuclear membranes reform

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6
Q

Trisomy 21 - genetic causes

A

Down’s syndrome

95% - primary trisomy 21 - non-dysjunction at meiosis
3% - robertsonian translocation of chromosomes 14 and 21
1% - mosaicism

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7
Q

Features of Down’s

A

Raised nuchal translucency
Dysmorphic features: small ears, upslanting palpebral fissures, flat facial profile, brachycephaly
Hypotonia
Cardiac abnormalities - ASD, VSD, persistent ductus arteriosus, tetralogy of fallot
GIT abnormalities: Duodenal atresia, imperforate anus, hirschsprung’s disease
Conductive hearing loss

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8
Q

Long-term diseases associated with Down’s

A

Alzheimer’s
AML/ALL
Hypothyroidism

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9
Q

Maternal risk of Down’s

A

25 years old: 1:1500

30: 1:900
35: 1:350
40: 1:100
45: 1:30
50: 1:11

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10
Q

Trisomy 18

A

Edward’s syndrome

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11
Q

Edwards syndrome: Prevalence and M:F ratio

A

1:3000 live births, M:F 1:2

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12
Q

Edwards: MSK defects

A

Rockerbottom feet, overlapping fingers, limb defects

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13
Q

Edwards: facial defects

A

Micrognathia, cleft lip, cleft palate

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14
Q

Edwards: cardiac defects

A

VSD
ASD
Patent ductus arteriosus

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15
Q

Edwards: Abdominal defects

A

Exomphalos
Inguinal hernia
Diaphragmatic hernia
Renal malformations

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16
Q

Edwards: intrauterine

A

Causes intrauterine growth restriction

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17
Q

Edwards: mortality rates

A

1 month: 30%
2 months: 50%
1 year: 90%

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18
Q

Trisomy 13

A

Patau’s syndrome

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19
Q

Prevalence of Patau

A

1:5000

Increases with maternal age

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20
Q

Features of Patau

A 
MIDLINE:
Hypotolerism (eyes close together)
Holoprosencephaly (failure of prosencephalon to develop into two hemispheres
Cleft lip
Cleft palate
Scalp defects
Post-axial polydactyly
Congenital heart defects
Renal abnormalities
Omphalocele
Intrauterine growth restriction
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21
Q

Mortality rate Patau

A

Almost 100% by 1 month of age

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22
Q

Sex chromosome aneuploidies examples

A

Klinefelter (XXY)

Turner (X0)

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23
Q

Turner’s syndrome: prevalence

A

1:2500 female live births

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24
Q

Features of Turner’s syndrome

A 
Raised nuchal translucency
Cystic hygroma
Lymphoedema
Neck webbing
Short stature
Shield shaped chest, widely spaced nipples
Coarctation of aorta
Gonadaldysgenesis
Renal abnormalities inc horseshoe kidney
Intellectually NORMAL
Risk of gonadoblastoma
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25
Q

Klinefelter’s syndrome, incidence

A

1:1000 live births

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26
Q

Features of Klinefelter’s

A

Tall
Small testes, hypogonadotrophic hypogonadism
Infertility

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27
Q

Structural chromosomal abnormalities caused by deletion: 22q11 (+ features)

A

DiGeorge syndrome

Immune deficiency
Hypocalcaemia due to parathyroid dysfunction
Autism
Congenital heart disease
Cleft lip +/palate
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28
Q

Structural chromosomal abnormalities caused by deletion: 15q11-13 - maternal

A

Angelman

Happy!
Macroglossia
Ataxia
Seizures
Learning difficulties
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29
Q

Structural chromosomal abnormalities caused by deletion: 15q11-13 - paternal

A

Prader-Willi

Obese
Hypogonadism
Hypotonia

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30
Q

Give some examples of autosomal dominant inherited conditions

A 
Myotonic dystrophy
Huntington's
Tuberous Sclerosis
Polycystic Kidney Disease
Neurofibromatosis 1 + 2
Achondroplasia
Marfan's syndrome
Osteogenesis imperfecta
Porphyria
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31
Q

Examples of autosomal recessive conditions

A 
Cystic Fibrosis
Sickle cell disease
Thalassaemia
Phenylketonuria
Glycogen storage disorders
Congenital adrenal hyperplasia
Wilson's disease
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32
Q

Examples of X-linked recessive conditions

A

G6PD deficiency
Duchenne muscular dystrophy
Fragile X syndrome
Christmas disease (factor XI deficiency)
Haemophilia A + B (factors VIII + IX deficiency)
Neurogenic diabetes insipidus
Lesch-Nyhan syndrome (excess uric acid - gout, kidney stones, a bit dumb)
Wiskott-Aldrich syndrome (immune deficiency, thrombocytopenia, eczema)

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33
Q

X-linked recessive inheritance

A

1:2 sons of carrier females

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34
Q

X-linked dominant: inheritance

A

1:2 offspring of affected females

35
Q

X-linked dominant conditions

A

Severe in males: neonatal death

Incontinentia pigmenti
Rett syndrome
Vitamin D resistance rickets (otherwise known as hypophosphatemic rickets)

36
Q

Mitochondrial inheritance - features

A

Can affect both sexes but only passed on by affected mothers

37
Q

Examples of mitochondrial conditions

A

Leber’s hereditary optic neuropathy

Leigh’s syndrome - psychomotor regression

38
Q

What is tuberous sclerosis

A

Rare multisystem genetic disease causing tumour growth

39
Q

Tuberous sclerosis genetics

A

Mutation in either:
TSC1 (codes for hamartin) on chromosome 9
TSC2 (codes for tuberin) on chromosome 16

These proteins suppress tumour growth. Therefore mutations lead to tumours

40
Q

Features of tuberous sclerosis

A

Angiofibromas
Hypomelanotic macules
Shagreen patches (leathery patches of skin)
Ungal fibromas

Brain: Subependymal nodules, cortical tubers, epilepsy

Learning difficulties
Cardiac rhabdomyomas
Renal angiomyolipomas
Learning difficulties

41
Q

Cystic fibrosis genetics

A

Mutation in CFTR (CF transmembrane conductance regulator)
Chromosome 7
DeltaF508 is most common mutation

42
Q

Sickle cell disease: genetic cause

A

Point mutation in beta globin chain of haemoglobin

43
Q

Complications of sickle cell

A 
Vaso-occlusive crisis
Acute chest syndrome
Aplastic crisis
Splenic sequestration crisis
Haemolytic crisis (common in patients with co-existing G6PD deficiency)
44
Q

Types of alpha-thalassaemia

A

1 gene affected: silent carrier
2 genes: trait - mild hypochromic anaemia
3: Haemoglobin H disease - moderate anaemia and splenomegaly
4: Bart’s hydrops - intrauterine death

45
Q

Features of Beta-thalassaemia

A

Fatigue
Anaemia
Jaundice
Shortness of breath
Hepatosplenomegaly due to extramedullary haematopoiesis
Haemochromatosis - excess gut iron absorption

46
Q

QUADRUPLE TEST components

A

B-HCG
Inhibin
AFP
Unconjugated oestriol

47
Q

Down’s - quadruple test results

A

DECREASED AFP, UNCONJUGATED OESTRIOL

INCREASED B-HCG, INCREASED INHIBIN

48
Q

Earliest appropriate gestational age to perform CVS

A

11 weeks

49
Q

BRCA1 Breast cancer risk

A

60-90%

50
Q

BRCA2 Breast cancer risk

A

45-80%

51
Q

BRCA1 Ovarian cancer risk

A

40-60%

52
Q

BRCA2 Ovarian cancer risk

A

10-30%

53
Q

Which chromosomal abnormality has a known association with severely impaired semen quality?

A

Microdeletions on Y chromosome

54
Q

Spermatogenesis. Which cells can undergo mitotic division

A

Spermatogonia

55
Q

Combined test. When offered?

A

10-14 weeks

Often carried out at same time as 12 week scan

56
Q

Quadruple blood test, when offered

A

14-20 weeks

Not as accurate as combined test

57
Q

Combined test - findings in down’s

A

Raised nuchal translucency
Increase B-HCG
Low PAPP-A

58
Q

Syndrome caused by microdeletion of chromosome 5

A

Cri-du-chat

59
Q

Quadruple blood test findings in Edwards

A

ALL reduced

60
Q

Incidence of phenylketonuria

A

1 in 14,000

61
Q

Treatment of phenylketonuria

A

Dietary restriction of phenylalanine

62
Q

When to commence folic acid in beta thalassaemia patients

A

3 months prior to conception

63
Q

When should the Guthrie inhibition assay be taken

A

> 12hours after delivery

64
Q

Most common enzyme deficiency in CAH

A

21-hydroxylase

65
Q

Inheritance pattern of Lynch syndrome

A

Autosomal dominant

66
Q

CAH gene mutation

A

CYP21A

67
Q

What is the correct description of a chromosome when the p and the q arms are the
same length around the centromere?

A

Metacentric

68
Q

How many genes are there in the human genome?

A

Approximately 20000

69
Q

In meiosis, when does recombination of genetic material occur when considering
gamete production?

A

Prophase 1

70
Q

Which of the following statements describes meiosis?

a. Two daughter cells are generated which are genetically identical
b. Four daughter cells are generated which are genetically identical
c. Two daughter cells are generated from one dividing germ cell
d. Four daughter cells are generated from one dividing germ cell
e. One polar body is generated from one dividing germ cell

A

d. Four daughter cells are generated from one dividing germ cell

71
Q

Rocker bottom feet are associated with

A

Edward’s

72
Q

Karyotype results from CVS or fetal blood

A

Takes 48-72hrs

73
Q

Amniocentesis result back in

A

2-3 weeks

74
Q

Clinical features of myotonic dystrophy

A 
Frontal balding
Distal muscle weakness
Sterno-mastoid weakness
Gonadal atrophy
Cardiac conduction defects
Difficulty relaxing a clenched fist
Cardiac conduction defects
Retinopathy
75
Q

Pre-natal diagnosis of congenital adrenal hyperplasia

A

17-HP concencration in amniotic fluid

OR

DNA analysis from CVS or amnio

76
Q

Aneuploidy associated with Hashimoto’s

A

Turner’s

77
Q

Chromosomes involved in robertsonian translocation

A

Acrocentric:

13, 14, 15, 21, 22

78
Q

Telocentric chromosomes

A

Not seen in humans

centromere at one end

79
Q

Osteogenesis imperfecta inheritance pattern

A

Autosomal dominant

80
Q

AIS 46XY phenotype?

A

Female phenotype, normal breast development, absent uterus with blind-ending vagina; paucity of pubic and axillary hair

81
Q

Complications of AIS

A

Inguinal hernias

Abdominal/inguinal canal testes —> inc risk gonadoblastoma

82
Q

Haemoglobin electrophoresis - normal ranges

A
  • HbA 1: 95%-98%
  • HbA 2: 1.5%-3.5%
  • HbF: < 2% (age-dependent)
  • HbC: Absent
  • HbS: Absent
83
Q

Cystic fibrosis caucasian carrier rate

A

1:25

mrcog part 1 (14 decks)

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