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MCD Genetics > 2 Mr. Jones's (2) Risk of Transmission of Genetic Disease > Flashcards

2 Mr. Jones's (2) Risk of Transmission of Genetic Disease Flashcards

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Biology 101 flashcards
1
Q

Q: What are the 2 types of genetic disease? Give 3 features for each. (Inheritance, environment, occurrence)

A

A: Monogenic (defect of individual gene)

  • Clear inheritance
  • No environmental influence
  • Individually rare

Complex Disorders

  • No clear inheritance
  • Environment essential
  • Common
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2
Q

Q: List 3 examples of monogenic genetic diseases.

A

A: Huntington Disease, Cystic Fibrosis, Haemophilia

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3
Q

Q: List 3 examples of complex (disorders) genetic diseases.

A

A: Type 2 Diabetes, Schizophrenia, Crohn’s Disease

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4
Q

Q: What is Mendeleev inheritance?

A

A: The process whereby individuals inherit and transmit to their offspring one out of the two alleles present in homologous chromosomes

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5
Q

Q: What is an allele? What are different alleles described as? (2)

A

A: alternate forms of a gene or DNA sequence at the same chromosome location (locus)

Different alleles maybe described as MUTATIONS (not common in population) or POLYMORPHISMS (relatively common in population)

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6
Q

Q: What are Homologous Chromosomes?

A

A: matching (but non-identical) pair of chromosomes - one from each parent

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7
Q

Q: What is a mutation? What is a polymorphism? When are polymorphisms called mutations? Polymorphisms may contribute to?

A

A: Mutation - any heritable change in the DNA sequence

Polymorphism - a mutation at a >1% frequency in a given population.

Polymorphisms are usually still called mutations if they cause monogenic disease.

Polymorphisms may contribute to complex diseases

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8
Q

Q: What are the 2 main categories for mutations? Name 2 mutations within each?

A

A: Point Mutations:

  • Missense - mutation means that the codon changes to code for a different amino acid.
  • Nonsense - mutation means that the codon codes for a stop codon so the polypeptide chain ends prematurely.

Frame-shift Mutations:

  • Insertion - insertion of an extra base will cause the code to be shifted out of frame.
  • Deletion - deletion of a base
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9
Q

Q: What are frame-shift mutations also called?

A

A: Depending on what you consider a normal sequence, it can be either an insertion or a deletion. So they are sometimes referred to as InDel

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10
Q

Q: What are point mutations?

A

A: a single change in the DNA sequence

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11
Q

Q: Why should you take a family history? (5)

A

A: -identify genetic diseases in family

  • identify inheritance patterns
  • aid diagnosis
  • assist in management of conditions
  • identify relatives at risk of a disease (need to consider screening)
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12
Q 
Q: Pedigree diagram. 
Square? 
Circle? 
Diamond?
White?
Black?
Line from bottom left to top right? 
Number within?
P within?
Triangle?
Arrow pointing at it?
A 
A: male
female
unknown sex
unaffected
affected
dead
multiple
pregnant
miscarriage
person giving info
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13
Q

Q: What are the 5 types of Mendelian inheritance patterns? Which are the main 3? Which 2 are sex linked? Which is rare?

A

A: 1 Autosomal Dominant

2 Autosomal Recessive

3 X-linked Dominant (RARE)

(4) X-linked Recessive
(5) Mitochondrial

3 and 4 are sex linked

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14
Q

Q: How do you draw a family pedigree? (4)

A

A: 1 build tree from bottom starting with affected person and siblings (inc names and DoBs)
2 one side of family (ask about their siblings and their children)
3 then other side
4 ask about chn with other partners

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15
Q

Q: In autosomal dominant inheritance, how many parents are affected? Which parent transmits it? Which sex child is affected? Transmission type? Carriers? Chance of being affected if one parent is affected? Expressivity?

A

A: at least 1

either

either

vertical transmission

don’t get carriers

50% (explained with punnet square)

varied (severity)

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16
Q

Q: Describe Huntington’s disease as an autosomal dominant disease. Main feature? Mean age of onset? Median survival time after onset? Treatment? Down the generations?

A

A: Motor, Cognitive and Psychiatric dysfunction - hyperkinesia

35-44

15-18

can ease symptoms but not cure

get genetic anticipation

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17
Q

Q: What is the 4 step Huntington’s disease mechanism? Not?

A

A: 1. HTT gene on Chr 4 encodes a protein called huntingtin.

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

not loss of gene

18
Q

Q: What is genetic anticipation? (2)

A

A: down the generations:

  • age of onset decreases
  • severity increases (also seen in myotonic dystrophy)
19
Q

Q: What is the molecular basis of Huntington’s disease? (3)

A

A: Caused by an unstable triplet repeat (CAG)

Number of repeats may EXPAND with each generation

More Repeats = More Likely to be Affected

40-120 repeats = affected
35-40 = sometimes either way

20
Q

Q: In autosomal recessive inheritance, how many affected parents are there? Which parent transmits it? Which sex child is affected? Family history? Risk of child being affected/carrier?

A

A: None

either

either

usually no family history

affected = 25%. carrier = 50%

21
Q

Q: Describe cystic fibrosis as an autosomal recessive disease. (3) Treatment. How many people in UK are carriers?

A

A: -chronic, life threatening

  • Thick mucus in lungs causes breathing problems and repeated infections.
  • Blockages in pancreas affect digestive enzymes.

daily enzymes and physiotherapy

1 in 22

22
Q

Q: What is the 4 step Cystic Fibrosis mechanism?

A

A: 1. CFTR gene on Chr 7 encodes a protein called Cystic Fibrosis Transmembrane Conductance Regulator (CFTR).

  1. CF patients inherit two copies of mutated CFTR gene.
  2. Absence of functional CFTR protein affects chloride ion function in epithelial cells.
  3. Disruption of Salt/Water regulation causes thick mucus and leads to symptoms.

(absence of functioning protein causes disease)

23
Q

Q: What is the molecular basis of cystic fibrosis? (3)

A

A: Most common mutation = delta F508

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

CF testing is part of UK newborn screening programme

24
Q

Q: What is CAVD? Most cases are caused by?

A

A: Congenital Absence of the Vas Deferens (CAVD)
-condition in which the vasa deferentia fail to form properly -> Causes infertility

MOST CASES OF CAVD ARE CAUSED BY MUTATIONS IN THE CFTR GENE!

25
Q

Q: In X-linked recessive inheritance, how many affected parents are there? Which parent transmits it? Which sex child is affected? Why? Results in inheritance?

A

A: normally none

female carrier

Only males (if they get the faulty gene, they don’t have another allele for it while females do)

sons have 50% chance of being affected
females have 50% chance of being carrier

26
Q

Q: Describe haemophilia as an X-linked recessive disease. Disorder of? Symptoms? Types? Treatment?

A

A: blood clotting disorder

affected people bruise easily and bleed for longer

Two main types: A and B

Can be successfully treated with injections of clotting factor

27
Q

Q: What is the 3 step Haemophilia mechanism?

A

A: 1. The F8 gene on Chr X encodes a protein called coagulation factor VIII.

  1. Boys with haemophilia A inherit one copy of a mutated form of the F8 gene.
  2. Lack of functioning Factor VIII causes symptoms of disorder.
28
Q

Q: Compare haemophilia A and B. B is caused by? Symptoms? Rarer?

A

A: Haemophilia B is caused by mutations in the F9 gene - also on the X chromosome.

F9 codes for coagulation factor IX

SYMPTOMS ARE IDENTICAL TO THOSE OF HAEMOPHILIA A

Haemophilia B is much rarer

29
Q

Q: Give 3 examples of genetic heterogeneity.

A

A: Same gene, Different mutation, Different symptoms -e.g. CF and CAVD are both caused by mutations to the CFTR gene

Same disease, Different genes - e.g. Haemophilia A and B

Same disease, Different genes, Different inheritance patterns - e.g. different forms of epidermolysis bullosa can be autosomal dominant or autosomal recessive

30
Q

*Q: What is penetrance? measured by? incomplete?

A

A: the extent to which a particular gene or set of genes is expressed in the phenotypes of individuals carrying it, measured by the proportion of carriers showing the characteristic phenotype

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

31
Q

*Q: What is variable expressivity?

A

A: - disease severity may vary between individuals with the same disease-causing mutation

32
Q

*Q: What is phenocopy?

A

A: having the same disease but with a different underlying cause

33
Q

*Q: What is epistasis?

A

A: interactions between disease gene mutations and other modifier genes can affect the phenotype

34
Q

Q: What are dominant conditions usually caused by? (1 eg)

A

A: gene mutations that result in toxic protein (e.g. HD) - effects of the mutated gene MASK the normal copy

35
Q

Q: What are recessive conditions caused by? (2 egs)

A

A: absence of functional protein (e.g. CF, Haemophilia) - effects of the mutated gene are only seen because the normal copy is absent

36
Q

Q: People with co-dominant conditions have which effects present?

A

A: of both mutated and normal genes e.g. Sickle Cell Trait

37
Q

Q: How do you treat dominant and co-dominant conditions?

A

A: need to neutralise the effects of the toxic protein or switch off the mutant gene to UNMASK the normal gene

38
Q

Q: How do you treat recessive conditions?

A

A: need to restore the activity of the missing protein by replacing the gene or protein product or even affected tissues

39
Q

Q: Define consanguinity. (2) In which type of genetic inheritance is it seen?

A

A: property of being from the same kinship as another person. In that aspect, consanguinity is the quality of being descended from the same ancestor as another person

autosomal recesssive

40
Q

Q: What is Epidermolysis bullosa (EB)?

A

A: name for a group of rare inherited skin disorders that cause the skin to become very fragile. Any trauma or friction to the skin can cause painful blisters.

MCD Genetics (7 decks)

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