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Flashcards in Complex inheritance Deck (17):
1

Examples of non-Mendelian inheritance

- Gene conversion
- Incomplete penetrance
- Genomic inprinting
- Extranuclear inheritance
- Anticipation

2

Inheritance penetrance

Mechanisms: environmental factor, genetic modifiers

3

Genomic imprint mechanisms

- An epigenetic process
- Variants from parents, dependent on that parent
- Genes expressed from only one chromosome
- If an inherited allele from a parent is imprinted, it is silenced
- Only the allele from the other parent is expressed

4

Genomic imprinting can result in

- Deletions
- Point mutations
- Imprinting errors
- Uniparental disomy

5

Imprinting errors examples

- Angelman and Prader-Willi, same chromosomal region. Totally different syndromes

6

Angelman syndrome

- Epilepsy
- Severe mental retardation
- Awkward gait
- Inappropriate laughter
- Deletion on maternal chromosome or paternal UPD

7

Prader-Willi Syndrome

- Hypotonia
- Mental retardation (mild to moderate)
- Short stature
- Obesity
- Deletion on paternal side or maternal UPD

8

Uniparental disomy

- Inheritance of a chromosome pair from one parental origin

9

Effects of uniparental diploidy

- Gynogenic: 2 maternal genomes, mass of embryo, ovarian teratoma
- Androgenic: 2 paternal genomes, mass of placenta, molar pregnancy

10

Extranuclear inheritance

Mechanism:
- Mitochondria mutation due to higher mutation rate in mitochondria
- Lack of efficient DNA repair
- Lack of protective proteins, histones
- Damaged by free radicals

11

3 major myopathies

- Myoclonic epilpepsy with ragged red fibres (MEERF)
- Mitochondrial myopathy, encephalomyopathy, lactic acidosis, stroke-like symptoms (MELAS)
- Chronic progressive external opthalomoplegia (CPEO)

12

Non-myopathic diseases from extranuclear inheritance

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

13

Anticipation

Mechanism:
- Triplet repeat expansion
- Disease present at earlier age and/or increasing severity in succeeding generations
e.d. Huntington's, Myotonic dystrophy, Fragile X syndrome

14

Genetic penetrance definition

- Frequency with which a trait is manifested by individuals carry the gene

15

Cystic fibrosis

- Autosomal recessive
- CF phenotype is variable in terms of severity and affected organs
- Genetic modifiers: may involve polymorphism
- Environmental factors: lifestyle, diet, smoking, alcohol/drugs, stress, air pollution, infection

16

Genetic conditions are:

- Rare
- Genetics simple
- Uni-factorial
- High recurrence rate

17

Environmental conditions are:

- Common
- Genetics complex
- Multi-factorial
- Low recurrence rate