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Genetics > 2. Mrs Jones (2) - risk of transmission of disease > Flashcards

2. Mrs Jones (2) - risk of transmission of disease Flashcards

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Biology 101 flashcards
1
Q

Monogenic

A

Clear inheritance
No environmental influence
Rare

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2
Q

Give 3 examples of monogenic diseases

A

Huntington disease
Cystic fibrosis
Haemophilia

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3
Q

Complex disorders

A

No clear inheritance
Environment essential
Common

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4
Q

Complex disorders examples

A

Type 2 diabetes, Schizophrenia, Crohn’s disease

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5
Q

Mendelian Inheritance

A

Individuals inherit and transmit to their offspring 1 out of the 2 alleles present in homologous chromosomes

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6
Q

Allele

A

Alternate forms of a gene or DNA sequence at the same chromosome location (locus).

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7
Q

Homologous chromosomes

A

matching (but non-identical) pair of chromosomes -

1 from each parent

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8
Q

Different alleles maybe described as

A

MUTATIONS or POLYMORPHISMS

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9
Q

Mutation

A

any heritable change in the DNA sequence

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10
Q

Polymorphism

A

a mutation at a >1% frequency in a given population

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11
Q

Polymorphisms are usually still called mutations if

A

they cause monogenic disease

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12
Q

Point Mutations

A

A single change in the DNA sequence:
Missense
Nonsense
Frameshift

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13
Q

Missense mutation

A

Codon changes to code for a different amino acid

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14
Q

Nonsense mutation

A

Codon codes for a stop codon so polypeptide chain ends prematurely

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15
Q

Frame-shift Mutations

A

Insertion/ Deletion of an extra base will cause the code to be shifted out of frame

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16
Q

Why take a genetic family history?

A 
Identify genetic disease in a family
Identify inheritance patterns
Aid diagnosis
Assist in management of conditions
Identify relatives at risk of disease
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17
Q

5 Types of Mendelian Inheritance Patterns

A 
Autosomal Dominant 
Autosomal Recessive 
X-linked Dominant (RARE) 
X-linked Recessive 
Mitochondrial
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18
Q

Parent in Autosomal Dominant

A

At least 1 affected parent

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19
Q

Who can transmit or be affected by Autosomal Dominant diseases?

A

Transmitted by M or F

M or F affected

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20
Q

Chance of child being effected in Autosomal Dominant pattern

A

50%

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21
Q

Example of Autosomal Dominant disease

A

Huntington’s Disease

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22
Q

Huntington’s Disease

A

Motor, Cognitive and Psychiatric dysfunction - hyperkinesia
Age of Onset: 35 - 44 years
Survival Time: 15 - 18 years after onset (no cure)

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23
Q

Huntington’s Disease Mechanism

A
  1. HTT gene on Chr 4 encodes huntingtin protein.
  2. HD patient inherit 1 copy of a mutated form of the huntingtin gene.
  3. Altered gene encodes a toxic form of the protein that forms ‘clumps’.
  4. Cell death in basal ganglia of brain resulting in symptoms.
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24
Q

Patterns of inheritance with Huntington’s Disease

A

Age of Onset Decreases

Severity Increases

25
Q

Molecular basis of Huntington’s Disease

A

Caused by an unstable triplet repeat (CAG)

Number of repeats may EXPAND with each generation More Repeats = More Likely to be affected

26
Q

Parent and Family history in Autosomal recessive

A

No affected parent

Usually no family history

27
Q

Chance of child being effected in Autosomal recessive pattern

A

25% risk of child being effected

50% chance of child being carrier

28
Q

Example of Autosomal recessive disease

A

Cystic Fibrosis

29
Q

Cystic Fibrosis symptoms

A

Thick mucus in lungs causes breathing problems and repeated infections.
Blockages in pancreas affect digestive enzymes
Chronic, life threatening condition

30
Q

Cystic Fibrosis Mechanism

A
  1. CFTR gene on Chr 7 encodes Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein.
  2. CF patients inherit 2 copies of mutated CFTR gene.
  3. Absence of functional CFTR protein affects chloride ion function in epithelial cells.
  4. Disruption of Salt/Water regulation causes thick mucus & leads to symptoms
31
Q

What is the most common mutation causing CF?

A

ΔF508

Deletion affects folding of CFTR protein and prevents it moving to correct place in cell membrane

32
Q

Congenital Absence of the Vas Deferens (CAVD) is a condition in which vasa deferentia fail to form properly, what does it cause?

A 
Causes infertility (azoospermia) 
Affects 1/2500 men
33
Q

Whats the most common cause of CAVD?

A

MUTATIONS IN CFTR GENE

34
Q

Parent in X-Linked Recessive

A

No affected parents

35
Q

Who is effected in X-linked recessive?

A

Males

36
Q

Who transmits X-linked recessive diseases?

A

Carrier females

37
Q

X-linked recessive probabilities

A

Sons have a 50% risk of being affected

Daughters have a 50% chance of being a carrier

38
Q

X-linked recessive example

A

Haemophilia

39
Q

Haemophilia

A

Blood clotting disorder: affected bruise easily and bleed longer
2 main types: A and B

40
Q

Haemophilia Mechanism

A
  1. F8 gene on Chr X encodes coagulation factor VIII protein
  2. Boys with haemophilia A inherit 1 copy of a mutated form of the F8 gene.
  3. Lack of functioning Factor VIII causes symptoms of disorder
41
Q

What causes Haemophilia B?

A

Mutations in F9 gene - also on X chromosome.

F9 codes for coagulation factor IX

42
Q

Haemophilia A and B symptoms

A

ARE IDENTICAL

Haemophilia B is much rarer

43
Q

Same gene
Different mutation
Different symptoms

A

CF and CAVD

both caused by mutations to CFTR gene

44
Q

Same disease

Different genes

A

Haemophilia A and B

45
Q

Same disease
Different genes
Different inheritance patterns

A

Different forms of epidermolysis bullosa can be autosomal dominant or autosomal recessive

46
Q

Incomplete Penetrance

A

Symptoms NOT always present in an individual with a disease-causing mutation

47
Q

Variable Expressivity

A

Disease severity may vary between individuals with same disease-causing mutation

48
Q

Phenocopy

A

having same disease but with a different underlying cause

49
Q

Epistasis complications

A

Interactions between disease gene mutations and other modifier genes can affect phenotype

50
Q

Epistasis

A

a type of gene action in which 1 gene can suppress action of another (nonallelic) gene

51
Q

Molecular mechanism of dominant conditions

A

usually caused by gene mutations that result in toxic protein (e.g. HD)
- effects of the mutated gene ‘MASK’ the normal copy

52
Q

Molecular mechanism of recessive conditions

A

caused by mutations that result in absence of functional protein (e.g. CF, Haemophilia)
- effects of mutated gene only seen because normal copy is absent

53
Q

Molecular mechanism of co-dominant conditions

A

effects of both mutated and normal genes apparent in people with both e.g. Sickle Cell Trait

54
Q

Implications for treatment:

Dominant & Co-dominant Conditions

A

Need to neutralise effects of the toxic protein or switch off mutant gene to UNMASK the normal gene

55
Q

Implications for treatment:

Recessive Conditions

A

Need to restore activity of missing protein by replacing gene or protein product or even affected tissues

56
Q

Square in genetic pedigree

A

Male

57
Q

Circle in genetic pedigree

A

Female

58
Q

Coloured in symbol in genetic pedigree

A

Affected individual

59
Q

Bottom left to top right diagonal line through symbol in genetic pedigree

A

Deceased

Genetics (7 decks)

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