Non-Mendelian Inheritence Flashcards
Define Incomplete Penetrance
When some people with a disease-causing mutation (change) in a gene develop the disease while others don’t.
What are the mechanisms for incomplete penetrance?
Environmental factor
Genetic Modifiers
Define genomic imprinting
The process by which only one copy of a gene in an individual (either from their mother or their father) is expressed, while the other copy is suppressed.
What are the mechanisms for genomic imprinting?
Variants from parents
Give an example of extranuclear inheritance.
Mutations in the mitochondria
Define Anticipation Inheritance.
A phenomenon in which the signs and symptoms of some genetic conditions tend to become more severe and/or appear at an earlier age as the disorder is passed from one generation to the next.
Define complex inheritance.
Multiple genes working together
Define penetrance
Penetrance is the frequency with which a trait is manifested by individuals carrying the gene.
For example, if there are 12 mutants and only 4 carry the symptoms, the penetrance is 4/12 so 33%.
Name a disorder which has a high penetrance.
Cystic Fibrosis
Is cystic fibrosis dominant or recessive?
Autosomal recessive
List some environmental factors which can contribute to cystic fibrosis.
Lifestyle, Diet, Smoke, Alcohol, Drug,
Stress, Air pollution, Chemicals,
Infection, etc.
What are genetic modifiers?
Genes that have small quantitative effects on the level of expression of another gene.
What are epigenetic modifications
Heritable changes in gene function not explained by changes in DNA sequences
What is epigenetic modification mediated by?
Methylation.
->don’t need to know necessarily but so you know what you’re on about-
the transfer of four atoms - one carbon atom and three hydrogen atoms (CH3) from one substance to another
Name some mechanisms which can cause a disorder of imprinting.
Deletions
Point mutations
Imprinting errors
What is meant by uniparental disomy?
Where you end up with two copies of one parent’s chromosome.
Inheritance of a chromosome pair from one parental origin
What happens if you get deletion of a maternal copy of a gene?
You would end up w no working copy
What happens if you have deletion of a parental copy of a gene?
No difference
Where do we inherit our mitochondria from?
Mother in egg cells- any mitochondria in the sperm degrades
What is the mutation rate of the mitochondria like?
Very high
Why does mitochondria have a high mutation rate?
Lack of DNA repair system.
Lack of protective proteins like histones so more exposed to free radicals.
Define homoplasmy
When an individual has all the normal copies of their mitochondrial genome.
Define Heteroplasmy.
When you have two or more mitochondrial DNA which have an odd genetic alteration or mutation within them.
What type of tissues do mitochondrial DNA tend to attack?
Affect tissues with high metabolic demand.
Name three major myopathies.
-Myoclonic epilepsy with ragged red fibers (MERRF)
-Mitochondrial myopathy, encephalomyopathy, lactic acidosis, stroke-like symptons (MELAS)
-Chronic progressive external ophthalmoplegia (CPEO)
*ragged red fibres are the appearance on histology
Multigenic/complex inheritance is often seen in individuals with?
Heart disease
Breast cancer
Autism
