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CELS 191 > Human disease genetics > Flashcards

Human disease genetics Flashcards

1
Q

What is a mutation

A

a permanent change to the DNA sequence

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2
Q

Why are vast majority of mutations neutral and have no effect at all

A

Because our genome is very large but the functional part is very small so there is a bigger chance of mutation occurring at a non-functional part of genome

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3
Q

Relate different ways in which mutations can be inherited

A

Germline mutations are inheritable. This is when mutations occur in cells that produce gametes and therefore can be inherited by the next generation

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4
Q

Silent mutation - define & where does it occur

A

Mutation with no effect on phenotype
Often occur in non-coding regions such as the intergenic regions and introns
Can occur in exons but can also cause no effect due to the redundancy of the genetic code

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5
Q

Missense mutations

A

Mutation that causes a change in amino acid due to changing a base that often does not produce serious phenotype alterations
Can change the sequence of protein and thus altering the protein’s ability to function
Can also have no effect if the amino acid changed was replace by a very similar one that does not alter the protein’s ability to function

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6
Q

Frameshift mutations

A

Insertion or deletion of a single base in a coding region that changes the readout of DNA so that the resulting protein is altered from that point on

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7
Q

Nonsense mutation/truncated mutation

A

Special case of point mutation when the base change results in the formation of a STOP codon resulting in truncated protein

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8
Q

Sickle cell anaemia is caused by what type of mutation

A

missense mutation

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9
Q

Triplet repeat expansion

A

Where a region containing triplet repeats undergo a catastrophic expansion that can alter protein function of destabilise a chromosome

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10
Q

Point mutation (single nucleotide polymorphism)

A

Single base change to NA sequence

Can result in change to amino acid but are mostly ‘silent’

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11
Q

Loss of function mutation

A

A mutation in the organism’s DNA resulting in the formation of either a protein that non longer functions, or complete loss of protein

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12
Q

Gain of function mutation

A

When the DNA sequence is altered so the protein becomes more active or takes on a new function

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13
Q

Example of loss of function mutation

A

Cystic fibrosis

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14
Q

Example of gain of function mutation

A

Huntington’s disease (triplet expansion)

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15
Q

somatic mutations

A

Changes to the DNA sequence of non-germline cells that are only inherited by daughter cells after division

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16
Q

Example of monogenic diseases

A

Haemophila A and B
Huntington Disease
Cystic fibrosis

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17
Q

What is haemophilia

A

disorders of blood clotting

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18
Q

Haemophilia A - effect, cause

A

Affects 1/5000 males worldwide
Results form impaired or absent clotting factor VIII which is most commonly caused by a mutation of inversion in Factor VIII gene on the X-chromosome

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19
Q

Haemophilia B - cause, what happens if untreated and treatment

A

Defect of blood clotting factor XI
If untreated, there is high risk of death from uncontrolled bleeding
Treatment by intravenous infusion of missing protein

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20
Q

Both Haemophilia A and B are what type of disorders

A

X-linked recessive disorders (1 intact copy protects against disease)

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21
Q

Why are women rarely affected by haemophilia

A

Because women have 2 X-chromosomes

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22
Q

Sons of women who are carriers of Haemophilia have what probability of inheriting the disease

A

0.5

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23
Q

Genetic cause of Huntington Disease

A

Mapped to chromosome 4 - autosomal
Caused by expansion of a CAG triplet repeat in HTT gene (Huntington gene) which codes for glutamine (protein has long polyglutamine tract which cause it to become unstable)

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24
Q

Symptoms of Huntington’s Disease (3)

A

Progressive tumor
Involuntary movements
Neurodegeneration

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25
Q

When does Huntington’s Disease normally develop

A

Onset in mid-life - usually 30-50

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26
Q

Treatment for Huntington’s Disease

A

No effective treatment

27
Q

Inheritance of Huntington’s Disease

A 
Autosomal dominant (not sex-linked)
1 copy of the infected gene can cause disease, having a normal copy of the same gene is NOT protective
Only affected people can pass on the gene
28
Q

Genetic testing for Huntington’s Disease

A

PCR used to determine length of CAG

Variation in length of repeat determines whether or not one will develop the disease

29
Q

10-35 copies of the CAG repeat

A

Normal

30
Q

How many copies of CAG repeats indicate risk of descendants developing Huntington’s Disease

A

27-35

31
Q

36-40 copies of CAG repeat

A

risk of developing disease

32
Q

How many copies of CAG repeats indicate that Huntington’s disease will develop

A

40+ copies

33
Q

Cause of Cystic Fibrosis

A

Can be caused by many different mutations in CFTR gene (Cystic fibrosis transmembrane regulator) which is an chloride ion transporter
Most common = 3 base pair deletion/deltaF508 deletion (protein is abnormally processed, mislabeled so is not directed to the cell membrane and become degraded)

34
Q

What does the reduced function of CFTR protein cause

A

thickening of cell secretions

35
Q

State a method used for screening for Cystic Fibrosis

A

Increased saltiness of sweat causedy by CF mutation

36
Q

Symptoms of Cystic fibrosis (5)

A 
Lung infections
Pancreatic insufficiency
Congenital absence of vas deferens in males 
Salty tasting skin
Thick mucus
37
Q

Inheritance of Cystic fibrosis

A

Autosomal recessive (not sex linked) - one copy of normal gene can protect from inheriting the disease

38
Q

State a X-linked recessive disorder

A

Haemophilia A and B

39
Q

What are polygenic disorders

A

Disorders that involve several genes acting together or environmental factors interacting with genes

40
Q

Technique used to find polygenic disorders

A

Association study - where the DNA of people with disease and people without disease are sequenced and variants are identified

41
Q

Examples of polygenic disease (8)

A 
Ischaemic heart disease
Asthma
Hypertension
Some cancers
Diabetes
Multiple sclerosis 
Bipolar disorder
Rheumatoid arthritis
42
Q

Genetic determinism

A
  • In polygenic disease, having a disease-related variation does not mean you will get the disease, such diseases come about through a combination of variants and the environment
  • Most genetic disorders are probabilistic not deterministic
43
Q

Synteny

A

When genes are present in the same order on chromosome of different species, indicating a common ancestor

44
Q

CNV (copy number variant)

A

Site in the genome at which individuals of the same species have different number of copies of a gene or genetic region instead of the standard 2 copies

45
Q

InDel

A

Variation in genome arising from insertion or deletion of base pair

46
Q

SNP (Single Nucleotide Polymorphism)

A

Site at which individuals of he same species have a different base pair in their genome

47
Q

Outline sources of variation between individual human genomes (3)

A

CNV, InDel, SNP

48
Q

What can’t we learn from the human genome sequence

A

function of a gene

49
Q

How can we make mutants

A

by treating organisms with radiation or chemicals

50
Q

Reasons for selected model organisms for genetics (3)

A

closely related to us
have rapid life cycles
can be domesticated

51
Q

What is a transgenic animal

A

model organism that has been engineered to carry an extra copy of DNA or transgene by random integration

52
Q

Example of mouse disease model

A

Cystic fibrosis

53
Q

Disadvantages of the mouse disease model for cystic fibrosis

A
  • Pancreatic disease not replicated
  • Males not infertile
  • Mouse died of gastrointestinal complications whereas humans die of lung disease
  • Lung disease only develops after long term exposure to pathogens
54
Q

Advantages of the mouse disease model for cystic fibrosis

A

Able to test therapies on mice

  • Drug therapy (treat the chronic symptoms)
  • Gene therapy (repair or replace the damaged CFTR protein)
55
Q

Define totipotent

A

Able to give rise to any cell type

56
Q

Homologous recombination

A

when the targeted gene recombines with the targeting vector and is removed

57
Q

Homologue

A

Gene that share similar sequence and function

58
Q

knockout mouse

A

mouse engineered by homologous recombination to lack a particular gene

59
Q

Model organism

A

an animal used by geneticists to link genotype to phenotype, using reverse and forward genetics

60
Q

Null

A

a non-functional gene allele

61
Q

Reverse genetics

A

when we disrupt the function of a known gene in order to work out what its purpose is

62
Q

Differentiation

A

The process by which cells become adapted ad tied to one function

63
Q

iPS cell

A

a pluripotent cell made by manipulating a differentiated cell

CELS 191 (8 decks)

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