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MBChB Phase 3 > Week 1: Genetics > Flashcards

Week 1: Genetics Flashcards

1
Q

Autosomal Dominant

A

Genetic disorder transferred from parent to offspring. Vertical pedigree pattern, expressed in heterozygotes, variable expressivity, may be incomplete penetrance.
Eg genetic breast/colon cancer

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2
Q

Autosomal recessive

A

Musy be homozygous to show phenotype. Horizontal pedigree pattern, expressed in homozygotes, may be consanguinity.
Eg Sickle Cell Anaemia, Cystic Fibrosis

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3
Q

X-linked

A

RECESSIVE: affects males, show Knight’s move pattern, all daughters carriers
DOMINANT: vertical transmission, all daughters affected

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4
Q

Variable inheritance

A

individuals in the same family are affected differently by the same gene

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5
Q

Incomplete penetrance

A

Severity of the same mutation differs from person to person. Common in autosomal dominant conditions

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6
Q

Genetic Anticipation

A

increased severity and earlier age of onset of mutation through generations. Eg Huntington’s

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7
Q

Mitochondrial inheritance

A

Genetic material only comes from mother. Disorders tend to affect the muscles, brain and eyes

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8
Q

What does the future of medical genetics involve?

A 
NIPT/NIPD
Next Generation Sequencing of whole exomes
Personalised Medicine
Treating specific genes 
Tailoring treatments to tumour genotypes
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9
Q

What does gene therapy involve?

A

Exon skipping in DMD (so you convert DMD to BMD)
Gene editing in CRISPR-CAS9 system
Base editing

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10
Q

How do you do a pre-implantation diagnosis?

A

remove a couple of cells at 3 days then use PCR/FISH to look at the DNA

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11
Q

What is genetic counselling?

A

It provides advice or information. The advice should be non-directive

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12
Q

Explain genetic screening

A

The whole population is offered a genetic test. It can be:
Prenatal (US, maternal blood markers)
Neo-natal (blood spot from heel, Guthrie card, mass spectrometry)
Post Natal (Tay Sachs for Jewish people)

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13
Q

What is heteroplasmy?

A

Presence of more than one type of organellar genome (mitochondrial DNA or plastid DNA) within a cell or individual

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14
Q

What are the symptoms of Huntington’s disease

A

progressive chorea (jerking/writhing movements), dementia, psychiatric symptoms, muscle dystonia, slow or abnormal eye movements

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15
Q

Genetics of Huntington’s

A

Autosomal dominant w/ genetic anticipation.

Caused by unstable length of chromosome 4 by CAG codon repeats

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16
Q

What are the symptoms of myotonic dystrophy?

A

progressive muscle weakness, myotonia, cataracts, ptosis

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17
Q

Genetics of myotonic dystrophy

A

Autosomal dominant w/ genetic anticipation

Unstable length of CTG repeat (causing abnormal DMPK mRNA)

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18
Q

What is cystic fibrosis?

A 
Thicker mucus (recurrent lung infections)
CFTR mutation causes defective chloride ion channel which makes mucus thicker.
Autosomal recessive
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19
Q

What is neurofibromatosis

A

Symptoms: cafe au lait macules, neurofibromas, short stature
Autosomal dominant
Complications: hypertension, scoliosis

20
Q

What are Duchenne Muscular Dystrophy and Becker’s Muscular Dystrophy?

A

X linked recessive, show knight’s move pattern
Creatinine kinase leaks out of damaged muscle into the blood
Symptoms: Muscle weakness, difficulty standing, unsteady, waddling gait.
DMD = out of frame reading mutation
BMD = in frame reading mutation

21
Q

What is Fragile X syndrome?

A

X linked recessive disorder w/ genetic anticipation. Is on the FMR1 gene
Inherited condition characterised by an X chromosome that is abnormally susceptible to damage, especially by folic acid deficiency. Affected individuals tend to have limited intellectual functions.

22
Q

What is Down’s Syndrome?

A

trisomy 21

symptoms: learning difficulty, heart defects, hypothyroidism

23
Q

What is trisomy?

A

This arises from maternal non-disjunction. The risk increases with maternal age

24
Q

What are the properties of a cancerous cell?

A

proliferative signalling; avoidance of apoptosis; bypass replicative senescence; insensitive to anti-growth signalling; needs its own blood supply

25
Q

What are the functions of Tumour Suppressor Genes?

A

Act as brakes; inhibit progression through the cell cycle and cell proliferation; promote apoptosis; act as stability genes

26
Q

What is a stability gene?

A

a type of tumour suppressor gene that acts to minimise genetic alterations

27
Q

What are proto-oncogenes

A

these participate in normal cellular resposne to growth factors. They stimulate the cell cycle to promote cell division/growth. Activation by mutation turns them into oncogenes

28
Q

Name the types of cancer and explain what they are

A

SPORADIC: common, late onset, single primary tumour
FAMILIAL: uncommon, early onset, often have multiple primary tumours

29
Q

What is DNA methylation?

A

This switches off a gene without changing the sequence

30
Q

What genes can cause breast cancer?

A

BRCA1, BRCA1, TP53, PALB2

31
Q

What is the function of BRCA1/2?

A

repair by homologous recombination of double stranded breaks

32
Q

What genes cause ovarian cancer?

A

BRCA1, BRCA2, HNPCC, PTEN

33
Q

What is the treatment of ovarian cancer?

A

PARP inhibition (olapirib). This blocks all types of DNA repair which forces the cells to die. It only kills tumour cells

34
Q

Colon cancer

A

Genetics: autosomal dominant, MLH1, MSH2, MSH6
Screening: colonoscopies every 2 years after 25 years

35
Q

What is familial adenomatous polyposis?

A

A faulty APC gene on chromosome 5

The bowel is full of small tumours - these can become malignant so you must remove the large bowel

36
Q

What is Li Fraumeni Syndrome?

A

Autosomal dominant cancer predisposition syndrome

There is a mutation in TP53 which can cause a range of cancers

37
Q

What is supercoiling?

A

DNA is tightly wound around a nucleosome made of histones (like beads on a string)

38
Q

What is RNA/DNA polymerase?

A

RNA polymerase = RNA making enzyme

DNA polymerase = DNA making enzyme

39
Q

What does tRNA do?

A

It carries amino acids which link together

40
Q

What does splicing do?

A

It gets rid of introns

41
Q

What are some examples of post translational modification?

A

Glycosylation, peptide bond cleavage, protein splicing, lipidation, sumoylation [ie adding sugar, glucose, lipids]

42
Q

What is X inactivation?

A

The X chromosome is switched off. This is triggered by the Xist gene

43
Q

Give examples of DNA based detection

A

Detection of point mutations: DNA sequencing, ARMS PCR
Detection of sub-microscopic duplications and deletions: MLPS, aCGH
Rapid detection of aneuploidies: QF-PCR

44
Q

Give examples of chromosome based analysis

A

Karyotyping, Fluorescence In-Situ Hybridisation (FISH)

45
Q

Give examples of DNA sequencing

A

Sanger sequencing, Next Generation Sequencing (Illumina method)

46
Q

What are the stages of data analysis?

A

DNA —(massively parallel sequencing, eg Illumina)—> FASTQ file —(sequence alignment)—> BAM file —(variant calling, identification)—> VCF file —(data filtering steps, eg removing common variants)

MBChB Phase 3 (15 decks)

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