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CMP > Genetics And Disease > Flashcards

Genetics And Disease Flashcards

0
Q

What are the types of genetic disease?

A

Germline:
Chromosomal, mitochondrial, monogenic, polygenic.
Somatic:
Cancer, mosaics, chimeras.

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1
Q

Describe the process of cytogenetic analysis.

A
  1. Centrifuge blood.
  2. Treat with hypotonic solution.
  3. Fix and stain (banding).
  4. Examine under the microscope.
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2
Q

What percentage of offspring will be affected in an autosomal dominant disease family tree with one parent sufferer?

A

1/2

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3
Q

What fraction of offspring will be affected with an autosomal recessive disease with two parent carriers.

A

1/4, 1/2 carriers.

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4
Q

What fraction of offspring will be affected with an X linked recessive disease with one parent carrier?

A

1/4 affected, 1/4 female carrier

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5
Q

What is the Hardy-Weinberg principle?

A

Both allele and genotype frequencies in a population remain in equilibrium from generation to generation unless specific disturbing influences are introduced.

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6
Q

Give examples of influences that may disturb the HW principle?

A

Non-random mating, mutations, selection, random genetic drift and gene flow.

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7
Q

What is the cause of Down’s syndrome?

A

Non-disjunction in female meiosis.

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8
Q

Which sex chromosome abnormality has the arrangement XXY?

A

Klinefelter’s syndrome.

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9
Q

Which sex chromosome abnormality has the arrangement XO?

A

Turners syndrome.

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10
Q

Name three imprinting disorders.

A

Prader-Willi, Angelman, Beckwith-Weidemann syndromes.

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11
Q

What is the sequence of events in classical genetics?

A

Disease –> biochemical defect –> gene product –> gene –> phenotype –> genotype.

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12
Q

What is the sequence of events in positional cloning/ reverse genetics?

A

Disease –> map position of gene –> gene –> gene product –> functional studies.
Genotype –> phenotype.

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13
Q

What was the purpose of gene mapping?

A

Develop a regional genetic map and select genomic clones.

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14
Q

How can we identify disease genes?

A

Examine candidate genes for mutation.
Disease gene will be mutated in infected individuals.
Mutation screening - SSCP analysis.
Direct sequencing.

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15
Q

What are the techniques of next generation sequencing?

A

Massive parallel sequencing of small fragments of DNA.

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16
Q

What is the most common gene mutation in cystic fibrosis?

A

70% see an increase in F508 - phenylalanine deletion.

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17
Q

What is a chromosomal defect?

A

Change in chromosome number or structure.

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18
Q

What is a mitochondrial disorder?

A

Mutation in mitochondrial DNA.

19
Q

What is a monogenic disorder?

A

Defects in a single gene.

20
Q

Name protein altered in cystic fibrosis. What does it do?

A

Cystic fibrosis transmembrane conductance regulator. ATP binding site, chloride channel.

21
Q

What is the protein involved in Duchenne Muscular Dystrophy? What does it do?

A

Dystrophin. Features in common with muscle structural proteins, links actin to a protein complex in the plasma membrane.

22
Q

What is the protein involved in Huntington’s disease?

A

Huntingtin.

23
Q

What is a trinucleotide repeat disorder eg Huntington’s?

A

Disorders involving an (XYZ)n sequence.

Result of a rare mutation, experiences anticipation between generations (symptoms are increasingly severe.)

24
Q

What are the classes of trinucleotide repeat disorders? What do they do?

A

Fragile sites - increased methylation - reduced transcription.
Neurodegenerative - multiple effects on protein-protein interactions, toxic protein aggregates.
Myotonic dystrophy - RNA mediated effects.
Freidriech’s ataxia - reduced transcription of frataxin.

25
Q

Give two examples of haemoglobinopathies.

A

Sickle cell anaemia, thalassaemia.

26
Q

What is a polygenic disorder?

A

A complex or multifactoral disorder with many genes involved and both environmental and genetic factors.

27
Q

Define epistasis.

A

Interaction between genes.

28
Q

Define genetic heterogeneity.

A

Alternative genes leading to the same condition.

29
Q

What is the liability model?

A

All factors contributing to a disease are termed liabilities. In a population showing normal distribution of disease when all factors are combined, disease will develop above a certain threshold. Genetic factors shift the curve, increasing the likelihood of disease.

30
Q

What are the problems in genetic analysis of polygenic disorders?

A

Poor genotype/phenotype correlation because not all susceptible individuals are affected, and the disease can be just down to environmental factors (phenocopy).

31
Q

What is genetic heterogeneity?

A

Several different genes, some may have a major effect, others more minor.
Variable penetrance/expressivity.

32
Q

Outline the methods for identifying genes in polygenic disorders.

A

Candidate gene.
Linkage analysis.
Association studies.

33
Q

What are the approaches to identifying genes in type 1 diabetes?

A

Non-parametric allele sharing (sub-pair).
Animal models.
Genome-wide association studies.

34
Q

What approaches are taken to identify genes in type II diabetes?

A

Linkage studies.
Human models.
Genome-wide association studies.

35
Q

What are the genes associated with Alzheimer’s?

A 
Amyloid precursor protein (APP) (Chr21) - mutations in early onset families. 
Presenilin 1 (Chr14) and Presenilin 2 (Chr1) - mutations in early onset families. 
Apolipoprotein E (Chr19) - associated with early and late onset forms.
36
Q

What are the three types of somatic defects?

A

Cancer, mosaics, chimeras.

37
Q

What is a mosaic?

A

More than one population of cells of the same genetic origin. Caused by non-disjunction in embryogenesis.

38
Q

What is a chimera?

A

More than one population of cells of different genetic origin. Eg dispermic, or the exchange of blood between non-identical twins in utero.

39
Q

What are the techniques for prenatal testing?

A

Amniocentesis - remove amniotic fluid and grow foetal cells. Takes weeks.
Chorionic villus - remove part of the chorionic villus, sufficient tissue for immediate analysis.

40
Q

What are the methods of adult and neonatal testing of blood?

A

Chromosome analysis

Molecular analysis: PCR based investigations of specific genes, indirect determination, DNA sequencing.

41
Q

What can be found with PCR-based investigations?

A

Deletions or point mutations (known or unknown mutations).

42
Q

Describe indirect determination.

A

Used when the gene is not cloned.
Relies on genetic linkage.
Allele linkage - due to founder effect, polymorphism always associated with mutation.
Locus linkage - work out linkage of a mutant allele to a polymorphic marker in a particular family. Can be unreliable, usually used in prenatal diagnosis.

43
Q

What are the possible treatments of genetic disease?

A

Physiotherapy and antibiotics (cystic fibrosis)
Surgery
Metabolic manipulation
Gene product replacement (insulin for diabetics, factor VIII in haemophilia)
Tissue and organ transplant (heart and lungs in CF)
Stem cell therapy.

44
Q

What is the theory of gene therapy?

A

Correction of a gene defect with a synthetic transgene.

45
Q

What are the vehicles that can be used to introduce the transgene into cells?

A

Viral vectors - retroviruses, adenoviruses, lentiviruses. Efficient but safety problems.
Physical methods - liposomes, receptor mediated endocytosis, direct DNA injection, can be inefficient compared to viral vectors, safe.

46
Q

What are the possible targets into which the transgene can be introduced?

A

Bone marrow - haemoglobinopathies.
Liver - metabolic defects.
Muscle cells - muscular dystrophy
Lung cells - cystic fibrosis in vivo.

CMP (4 decks)

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