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1.4 POM Genetics > Modes of Inheritance > Flashcards

Modes of Inheritance Flashcards

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
How do autosomal recessive alleles change a phenotype?
Loss-of-function
26
What is the chance of an autosomal recessive affected child having an affected sibling?
1/4
27
What type of pedigree pattern do autosomal recessive disorders have?
Horizontal
28
What increases the risk of autosomal recessive diseases in a family?
Cosanguineous marriages
29
What do cosanguineous marriages lead to and why?
Increased risk of autosomal recessive disorders in children - Smaller gene pool
30
What symbol represents disease gene frequency?
q
31
How do you calculate the risk of having an affected child via q?
1/q^2
32
How do you calculate the risk of having an affected 1st cousin of an affected child via q?
1/(q/16)
33
How does the prevalence of an autosomal recessive disease affect the risk of inheritance in cosanguineous marriages?
Less prevalent (rarer) ---> higher risk
34
What is an example of an autosomal recessive disease?
Cyctic fibrosis
35
What type of disease is cystic fibrosis?
Autosomal recessive
36
What are the 4 symptoms of cystic fibrosis?
1. Failure to thrive 2. Impaired airway defence 3. Prone to respiratory infections 4. Digestive issues
37
Which mutations cause cystic fibrosis?
CFTR gene mutations (chromosome 7) ---> codes for chloride ion channel
38
What is the result of CFTR gene mutations in cystic fibrosis?
Defective chloride ion channels (loss-of-function)
39
What are the sex chromosomes?
Chromosomes determining individual's sex - Females ---> XX - Males ---> XY
40
How many genes do X chromosomes contain?
1000-1300
41
How many proteins do X chromosomes code for?
850
42
How many genes do Y chromosomes contain?
850
43
How many proteins do Y chromosomes code for?
50-70
44
Which sex do X-linked disorders mainly effect and why?
Males - Only need 1 copy ---> effectively dominant
45
How are males with X-linked disorders connected?
Via females ∴ affected son may have affected maternal uncle
46
What is the chance of an X-linked affected son having an affected brother?
1/2
47
What is the chance of an X-linked affected son having a carrier sister?
1/2
48
What will daughters of an X-linked affected male all be?
Carriers
49
What are 2 examples of X-linked disorders?
1. Haemophilia (rec) 2. X-linked hypophosphatemia (dom)
50
What type of disease is haemophilia?
X-linked recessive
51
What type of disease is X-linked hypophosphatemia?
X-linked dominant
52
What causes haemophilia?
Issues with clotting factors VIII or IX
53
What is the main symptom of haemophilia?
More/worse bleeds
54
Do female carriers of X-linked disorders ever display symptoms?
Sometimes - If unaffected X chromosome inactivated
55
56
What are X-linked recessive disorders?
Need all X chromosomes affected for phenotypes - more common in males
57
What are the 5 symptoms of X-linked hypophosphatemia?
1. Rickets (vit D resistant) 2. Growth effects 3. Lower serum phosphorus 4. Osteomalacia 5. Fractures/pseudofractures
58
Which mutation leads to X-linked hypophosphatemia?
PHEX gene
59
Why does a PHEX mutation lead to X-linked hypophosphatemia?
FGF21 overproduced ---> inhibits kidney phosphate reabsorption + retention
60
Which sex do Y-linked disorders affect?
Males
61
What is the chance of a Y-linked affected father having an affected son?
1 ---> all
62
What pedigree pattern do Y-linked disorders display?
Vertical
63
What is an example of a Y-linked disorder?
Retinitis pigmentosa
64
What type of disease is retinitis pigmentosa?
Y-linked
65
What is the main symptom of retinitis pigmentosa?
Sight loss
66
Which mutation causes retinitis pigmentosa?
RPY gene
67
Why does a RPY mutation cause retinitis pigmentosa?
Retina cells produce defective protein
68
What is the main difference between the inheritance of X-linked recessive vs dominant disorders?
- Recessive ---> more males - Dominant ---> more females
69
What is mitochondrial endosymbiosis?
Mitochondria once existed as bacteria ---> taken up by eukaryotic cells
70
Why is mitochondrial disease inheritance different from other diseases?
Mitochondria have own DNA
71
What are most mitochondrial diseases caused by?
Mitochondrial DNA mutations (90%)
72
Why can some mitochondrial diseases be caused by mutations in nuclear genes?
Some autosomal/sex chromosome genes code for mitochondrial proteins
73
What type of inheritance do mitochondrial diseases display and why?
Maternal - Mitochondria inherited from mother
74
What is the chance of a mitochondrial affected mother having an affected child?
1 ---> all
75
What pedigree pattern do mitochondrial disorders display?
Vertical
76
Are mitochondrial conditions consistent within a family?
No ---> very variable
77
What is heteroplasmy?
Multiple types of mitochondrial DNA within an individual's cells
78
Why do mitochondrial diseases have so much variability?
Heteroplasmy - Some normal + some affected mitochondria - Each mitochondria must pass affected DNA threshold - Each cell must pass affected mitochondria threshold
79
How do mitochondria replicate?
Binary fission
80
What can happen to mutated mitochondrial genes during mitochondrial replication?
Gained or lost ∵ random segregation
81
What does the severity of a mitochondrial disease depend on?
Number of affected mitochondria
82
Why may mitochondrial diseases develop over time?
Accumulation of mutant mitochondria to pass threshold
83
Which functions are commonly affected by mitochondrial diseases? (2)
1. Motor 2. Nerve
84
What is an example of a mitochondrial disorder?
LHON (Leber's hereditary optic neuropathy)
85
What is the main symptom of LHON and why?
Visual loss in young adulthood - Degeneration of optic nerve and retina
86
Which sex is more commonly affected by LHON?
Males

1.4 POM Genetics (9 decks)

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