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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

24
Q

What is genomic imprinitng

A

Genes expressed from only one chromosome

Parent-of-origin dependent

25
What is 5’ Methylcytosine (mC)
Occurs from DNA methylation of cytosine | It induces the structural adaptation of chromosomal region so as to perpetuate altered activity states
26
What genetic mechanisms of error are there
Deletions Point mutations Imprinting errors Uniparental disomy
27
What is uniparental disomy
Inheritance of a chromosome pair from one parental origin
28
How can uniparental disomy occur
From: Non-disjunction of a trisomy zygote Duplication of a monosomy zygote Non-disjunction or duplication of disomy zygote
29
What does the recombination of a zygote formed from gamates that have undergone mitotic error produce
Partial uniparental disomy
30
What can uniparental diploidy cause
Gynogenic | Androgenic
31
Describe gyongeic
2 maternal genomes Mass of embryo Ovarian teratoma
32
Describe androgenic
2 paternal genomes Mass of placenta Hydatidiform mole
33
What chromosomal region is affected in angelman syndrome and prader-willi syndrome
15q11-13
34
What does angelman syndrome cause
``` Epilepsy Mental retardation (severe) Awkward gait Inappropriate laughter ```
35
What does prader-willi syndrome cause
``` Hypotonia Mental retardation (mild-moderate) Short stature Marked obesity ```
36
What causes angelman syndrome
Deletion of maternal region Paternal UPD Imprinting defect Point mutations
37
What causes prader-willi syndrome
Deletion of paternal region Maternal UPD Imprinting defect
38
How is mitochondria inherited
Maternal egg contains mitochondria Paternal mitochondria degrades upon fertilisation Thousands of maternal mitochondria is replicated per cell
39
Describe mitochondrial genetics
``` Circular form 16.6 kb 37 genes 2 rRNA 22 tRNA 13 coding genes ```
40
Why is the mitochondria a mutation hotspot
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
What is homoplasmy
Uniform mtDNA - no disease
42
What is hetrtoplasmy
2 or more mtDNA If low % mutation - no/mild disease High % mutation - disease
43
What is a myopathy
Disease of muscle tissue
44
What are the 3 major myopathies that can occur in mitochondrial disease
Myoclonic epilepsy with ragged red fibers (MERRF) Mitochondrial myopathy, encephalomyopathy, lactic acidosis, stroke-like symptons (MELAS) Chronic progressive external ophthalmoplegia (CPEO)
45
What other conditions can be caused by mitochondrial disease
Leber’s hereditary optic neuropathy (LHON) - loss of central vision Leigh’s syndrome - encephalopathy Diabetes mellitus and deafness (DAD)
46
How is a three parent embryo produced
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
When does anticipation present
Disease presents at earlier age and/or increasing severity in succeeding generations
48
Give examples of anticipation diseases
``` Triplet repeat diseases e.g. Huntington’s disease Myotonic dystrophy Fragile X syndrome ```
49
What gene is mutated in Huntington’s disease and how many repeats tend to be found
Huntingtin Repeat: (CAG)n Normal: 11 - 34 Mutant: 36 - 120
50
What gene is mutated in Myotonic dystrophy and how many repeats tend to be found
DMPK Repeat: (CTG)n Normal: 5 - 30 Mutant: 50 - 2000
51
What gene is mutated in Fragile X syndrome and how many repeats tend to be found
FMR1 Repeat: (CGG)n Normal: 6 - 50 Mutant: 60 - 1000

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