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1.4 POM Genetics > Modes of Inheritance > Flashcards

Modes of Inheritance Flashcards

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1
Q

What are the 6 types of inherited disorders?

A
  1. Autosomal dominant
  2. Autosomal recessive
  3. X-linked dominant
  4. X-linked recessive
  5. Y-linked
  6. Mitochondrial
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2
Q

What are autosomes?

A

Chromosomes not involved in determining sex (1-22)

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3
Q

What are autosomal dominant alleles?

A

Only 1 inherited for phenotype

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4
Q

Why are brown eyes dominant?

A

Even just 1 active OCA-2 gene —> enough melanin produced for brown eyes

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5
Q

What is the chance of an autosomal dominant affected parent having an affected child?

A

1/2

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6
Q

What type of pedigree pattern do autosomal dominant disorders have?

A

Vertical

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7
Q

How do autosomal dominant alleles change a phenotype? (3)

A
  1. Gain-of-function
  2. Dominant negative effect
  3. Haploinsufficient
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8
Q

What is a gain-of-function effect?

A

Gene makes protein with new function

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9
Q

What is a dominant negative effect?

A

Mutated gene produces protein that can’t bind properly (eg. dimers/multimers produced)

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10
Q

What is a haploinsufficient effect?

A

Loss of 1 allele copy —> not enough protein produced

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11
Q

What are 2 examples of autosomal dominant disorders?

A
  1. Huntington’s disease
  2. Hypertrophic cardiomyopathy
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12
Q

What are the 5 symptoms of Huntington’s disease?

A
  1. Difficulty concentrating
  2. Depression
  3. Stumbling
  4. Involuntary jerking
  5. Swallowing issues
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13
Q

When do Huntington’s disease symptoms usually start?

A

Age 30-50

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14
Q

What mutation causes Huntington’s disease?

A

CAG repeats —> multiple glutamines in huntingtin protein

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15
Q

Why does the CAG expansion cause Huntington’s?

A

Abnormal huntington protein aggregates in cells —> toxic to neurones —> cell death

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16
Q

How does hypertrophic cardiomyopathy affect the heart? (4)

A
  1. Thick heart muscles
  2. Reduced heart chamber volume
  3. Stiffer heart walls
  4. Sudden cardiac death
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17
Q

What type of genetic disorder is Huntington’s disease?

A

Autosomal dominant

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18
Q

What type of genetic disorder is hypertrophic cardiomyopathy?

A

Autosomal dominant

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19
Q

What is the most common mutation leading to cardiomyopathy?

A

MYH7 gene (β-myosin heavy chain)
- Also MYBPC3 —> mutated myosin binding protein c

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20
Q

Why does MYH7 mutation lead to hypertrophic cardiomyopathy?

A

Decreased ATPase activity —> reducing sliding velocity —> weaker cardiac muscle —> compensatory cardiac muscle growth

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21
Q

What happens to cardiac function in hypertrophic cardiomyopathy?

A

Reduced

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22
Q

Why does hypertrophy occur in hypertrophic cardiomyopathy?

A

Compensatory (weaker muscle)

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23
Q

What are carriers?

A

Those with 1 copy of recessive disorder allele —> can pass on disorder but don’t have it

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24
Q

What are autosomal recessive alleles?

A

Need 2 copies for phenotype

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25
Q

How do autosomal recessive alleles change a phenotype?

A

Loss-of-function

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26
Q

What is the chance of an autosomal recessive affected child having an affected sibling?

A

1/4

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27
Q

What type of pedigree pattern do autosomal recessive disorders have?

A

Horizontal

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28
Q

What increases the risk of autosomal recessive diseases in a family?

A

Cosanguineous marriages

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29
Q

What do cosanguineous marriages lead to and why?

A

Increased risk of autosomal recessive disorders in children
- Smaller gene pool

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30
Q

What symbol represents disease gene frequency?

A

q

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31
Q

How do you calculate the risk of having an affected child via q?

A

1/q^2

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32
Q

How do you calculate the risk of having an affected 1st cousin of an affected child via q?

A

1/(q/16)

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33
Q

How does the prevalence of an autosomal recessive disease affect the risk of inheritance in cosanguineous marriages?

A

Less prevalent (rarer) —> higher risk

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34
Q

What is an example of an autosomal recessive disease?

A

Cyctic fibrosis

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35
Q

What type of disease is cystic fibrosis?

A

Autosomal recessive

36
Q

What are the 4 symptoms of cystic fibrosis?

A
  1. Failure to thrive
  2. Impaired airway defence
  3. Prone to respiratory infections
  4. Digestive issues
37
Q

Which mutations cause cystic fibrosis?

A

CFTR gene mutations (chromosome 7) —> codes for chloride ion channel

38
Q

What is the result of CFTR gene mutations in cystic fibrosis?

A

Defective chloride ion channels (loss-of-function)

39
Q

What are the sex chromosomes?

A

Chromosomes determining individual’s sex
- Females —> XX
- Males —> XY

40
Q

How many genes do X chromosomes contain?

A

1000-1300

41
Q

How many proteins do X chromosomes code for?

A

850

42
Q

How many genes do Y chromosomes contain?

A

850

43
Q

How many proteins do Y chromosomes code for?

A

50-70

44
Q

Which sex do X-linked disorders mainly effect and why?

A

Males
- Only need 1 copy —> effectively dominant

45
Q

How are males with X-linked disorders connected?

A

Via females
∴ affected son may have affected maternal uncle

46
Q

What is the chance of an X-linked affected son having an affected brother?

A

1/2

47
Q

What is the chance of an X-linked affected son having a carrier sister?

A

1/2

48
Q

What will daughters of an X-linked affected male all be?

A

Carriers

49
Q

What are 2 examples of X-linked disorders?

A
  1. Haemophilia (rec)
  2. X-linked hypophosphatemia (dom)
50
Q

What type of disease is haemophilia?

A

X-linked recessive

51
Q

What type of disease is X-linked hypophosphatemia?

A

X-linked dominant

52
Q

What causes haemophilia?

A

Issues with clotting factors VIII or IX

53
Q

What is the main symptom of haemophilia?

A

More/worse bleeds

54
Q

Do female carriers of X-linked disorders ever display symptoms?

A

Sometimes
- If unaffected X chromosome inactivated

55
Q
A
56
Q

What are X-linked recessive disorders?

A

Need all X chromosomes affected for phenotypes
- more common in males

57
Q

What are the 5 symptoms of X-linked hypophosphatemia?

A
  1. Rickets (vit D resistant)
  2. Growth effects
  3. Lower serum phosphorus
  4. Osteomalacia
  5. Fractures/pseudofractures
58
Q

Which mutation leads to X-linked hypophosphatemia?

A

PHEX gene

59
Q

Why does a PHEX mutation lead to X-linked hypophosphatemia?

A

FGF21 overproduced —> inhibits kidney phosphate reabsorption + retention

60
Q

Which sex do Y-linked disorders affect?

A

Males

61
Q

What is the chance of a Y-linked affected father having an affected son?

A

1 —> all

62
Q

What pedigree pattern do Y-linked disorders display?

A

Vertical

63
Q

What is an example of a Y-linked disorder?

A

Retinitis pigmentosa

64
Q

What type of disease is retinitis pigmentosa?

A

Y-linked

65
Q

What is the main symptom of retinitis pigmentosa?

A

Sight loss

66
Q

Which mutation causes retinitis pigmentosa?

A

RPY gene

67
Q

Why does a RPY mutation cause retinitis pigmentosa?

A

Retina cells produce defective protein

68
Q

What is the main difference between the inheritance of X-linked recessive vs dominant disorders?

A
  • Recessive —> more males
  • Dominant —> more females
69
Q

What is mitochondrial endosymbiosis?

A

Mitochondria once existed as bacteria —> taken up by eukaryotic cells

70
Q

Why is mitochondrial disease inheritance different from other diseases?

A

Mitochondria have own DNA

71
Q

What are most mitochondrial diseases caused by?

A

Mitochondrial DNA mutations (90%)

72
Q

Why can some mitochondrial diseases be caused by mutations in nuclear genes?

A

Some autosomal/sex chromosome genes code for mitochondrial proteins

73
Q

What type of inheritance do mitochondrial diseases display and why?

A

Maternal
- Mitochondria inherited from mother

74
Q

What is the chance of a mitochondrial affected mother having an affected child?

A

1 —> all

75
Q

What pedigree pattern do mitochondrial disorders display?

A

Vertical

76
Q

Are mitochondrial conditions consistent within a family?

A

No —> very variable

77
Q

What is heteroplasmy?

A

Multiple types of mitochondrial DNA within an individual’s cells

78
Q

Why do mitochondrial diseases have so much variability?

A

Heteroplasmy
- Some normal + some affected mitochondria
- Each mitochondria must pass affected DNA threshold
- Each cell must pass affected mitochondria threshold

79
Q

How do mitochondria replicate?

A

Binary fission

80
Q

What can happen to mutated mitochondrial genes during mitochondrial replication?

A

Gained or lost
∵ random segregation

81
Q

What does the severity of a mitochondrial disease depend on?

A

Number of affected mitochondria

82
Q

Why may mitochondrial diseases develop over time?

A

Accumulation of mutant mitochondria to pass threshold

83
Q

Which functions are commonly affected by mitochondrial diseases? (2)

A
  1. Motor
  2. Nerve
84
Q

What is an example of a mitochondrial disorder?

A

LHON (Leber’s hereditary optic neuropathy)

85
Q

What is the main symptom of LHON and why?

A

Visual loss in young adulthood
- Degeneration of optic nerve and retina

86
Q

Which sex is more commonly affected by LHON?

A

Males

1.4 POM Genetics (9 decks)

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