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Principles of Disease > Genetic Basis of Complex Inheritance > Flashcards

Genetic Basis of Complex Inheritance Flashcards

1
Q

What does mendelian inheritance involve

A

The Law of Dominance
The Law of Segregation
The Law of Independent Assortment

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2
Q

What are the principles of non-mendelian inheritance

A

Does not fit in with Mendelian’s Law (e.g.

Gene conversion or Intermediate phenotype)

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3
Q

What kind of non-mendelian inheritance patterns are there

A

Incomplete Penetrance
Genomic Imprinting
Extranuclear Inheritance
Anticipation

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4
Q

What mechanisms cause incomplete penetrance

A

Environmental factor

Genetic Modifiers

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5
Q

What mechanisms cause genomic imprininting

A

Variants from parents

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6
Q

What mechanisms cause extranuclear inheritant

A

e.g. mitochondria mutations

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7
Q

What mechanisms cause anticipation

A

e.g. triplet repeat expansion

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8
Q

What is penetrance

A

The frequency with which a trait is manifested by individuals carrying the gene

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9
Q

What mutation causes cystic fibrosis (CF)

A

Mutation in CFTR

Autosomal recessive inheritance

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10
Q

What is the prevalence of CF in European Caucasians

A

1 in 2,500 (4% carriers)

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11
Q

What is the prevalence of CF in Africans

A

1 in 13,000

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12
Q

What is the prevalence of CF in Asians

A

Rare

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13
Q

How can the CF phenotype be variable

A

In severity and affected organs

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14
Q

What organs can be affected in CF

A 
Sinuses (sinusitis infection)
Lungs
Skin
Liver
Pancreas
Intestines
Reproductive organs
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15
Q

How are the lungs, skin, liver. pancreas and intestines affected in CF

A

Lungs - thick sticky mucus build up, bacterial infection and widened airways
Skin - sweat glads produce salty sweat
Liver - blocked biliary ducts
Pancreas - blocked pancreatic ducts
Intestines - cannot fully absorb nutrients

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16
Q

What are gene modifiers

A

Genes that have small quantitative effects on the level of expression of another gene
It may involve polymorphism

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17
Q

What environmental factors can affect the severity of CF in organs

A 
Lifestyle
Diet
Smoke
Alcohol
Drug
Stress
Air pollution
Chemicals
Infection
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18
Q

What else apart from genetic factors can explain the prevalence of increased diabetes

A

Rapid changes in lifestyle and risk factors such as:
Obesity
Unhealthy diets
Physical inactivity

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19
Q

What factors are seen in genetic diseases

A

Rare
Genetics simple
Uni-factorial
High recurrence rate

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20
Q

What factors are seen in enviromental diseases

A

Common
Genetics complex
Multi-factorial
Low recurrence rate

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21
Q

Give some examples of human diseases mainly caused by genetics

A

Haemophilia
Osteogenesis imperfecta
Huntington’s Disease
Familial motor neurone disease

22
Q

Give some examples of human diseases caused by both genetics and environmental factors

A

Manic depressive psychosis
Ischaemic heart disease
Ankylosing spondylitis
Peptic ulcer Diabetes

23
Q

Give some examples of human diseases mainly caused by enviromental factors

A

TB

Scurvy

24
Q

What is genomic imprinitng

A

Genes expressed from only one chromosome

Parent-of-origin dependent

25
Q

What is 5’ Methylcytosine (mC)

A

Occurs from DNA methylation of cytosine

It induces the structural adaptation of chromosomal region so as to perpetuate altered activity states

26
Q

What genetic mechanisms of error are there

A

Deletions
Point mutations
Imprinting errors
Uniparental disomy

27
Q

What is uniparental disomy

A

Inheritance of a chromosome pair from one parental origin

28
Q

How can uniparental disomy occur

A

From:
Non-disjunction of a trisomy zygote
Duplication of a monosomy zygote
Non-disjunction or duplication of disomy zygote

29
Q

What does the recombination of a zygote formed from gamates that have undergone mitotic error produce

A

Partial uniparental disomy

30
Q

What can uniparental diploidy cause

A

Gynogenic

Androgenic

31
Q

Describe gyongeic

A

2 maternal genomes
Mass of embryo
Ovarian teratoma

32
Q

Describe androgenic

A

2 paternal genomes
Mass of placenta
Hydatidiform mole

33
Q

What chromosomal region is affected in angelman syndrome and prader-willi syndrome

A

15q11-13

34
Q

What does angelman syndrome cause

A 
Epilepsy
Mental retardation
(severe)
Awkward gait
Inappropriate
laughter
35
Q

What does prader-willi syndrome cause

A 
Hypotonia
Mental retardation
(mild-moderate)
Short stature
Marked obesity
36
Q

What causes angelman syndrome

A

Deletion of maternal region
Paternal UPD
Imprinting defect
Point mutations

37
Q

What causes prader-willi syndrome

A

Deletion of paternal region
Maternal UPD
Imprinting defect

38
Q

How is mitochondria inherited

A

Maternal egg contains mitochondria
Paternal mitochondria degrades upon fertilisation
Thousands of maternal mitochondria is replicated per cell

39
Q

Describe mitochondrial genetics

A 
Circular form
16.6 kb
37 genes
2 rRNA
22 tRNA
13 coding genes
40
Q

Why is the mitochondria a mutation hotspot

A

Lack of efficient DNA repair system
Lack of protective proteins, such as histones
Damaged can be caused by reactive oxygen species (ROS), such as free radicals

41
Q

What is homoplasmy

A

Uniform mtDNA - no disease

42
Q

What is hetrtoplasmy

A

2 or more mtDNA
If low % mutation - no/mild disease
High % mutation - disease

43
Q

What is a myopathy

A

Disease of muscle tissue

44
Q

What are the 3 major myopathies that can occur in mitochondrial disease

A

Myoclonic epilepsy with ragged red fibers (MERRF)
Mitochondrial myopathy, encephalomyopathy, lactic acidosis, stroke-like symptons (MELAS)
Chronic progressive external ophthalmoplegia (CPEO)

45
Q

What other conditions can be caused by mitochondrial disease

A

Leber’s hereditary optic neuropathy (LHON) - loss of central vision
Leigh’s syndrome - encephalopathy
Diabetes mellitus and deafness (DAD)

46
Q

How is a three parent embryo produced

A

Healthy DNA removed from patients egg cell excluding faulty mitochondria
Patients DNA transplanted into donor egg with healthy mitochondria
Reconstructed egg fertilised with sperm in lab and implanted into patient

47
Q

When does anticipation present

A

Disease presents at earlier age and/or increasing severity in succeeding generations

48
Q

Give examples of anticipation diseases

A 
Triplet repeat diseases
e.g.
Huntington’s disease
Myotonic dystrophy
Fragile X syndrome
49
Q

What gene is mutated in Huntington’s disease and how many repeats tend to be found

A

Huntingtin
Repeat: (CAG)n
Normal: 11 - 34
Mutant: 36 - 120

50
Q

What gene is mutated in Myotonic dystrophy and how many repeats tend to be found

A

DMPK
Repeat: (CTG)n
Normal: 5 - 30
Mutant: 50 - 2000

51
Q

What gene is mutated in Fragile X syndrome and how many repeats tend to be found

A

FMR1
Repeat: (CGG)n
Normal: 6 - 50
Mutant: 60 - 1000

Principles of Disease (41 decks)

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