Non-Mendelian Inheritence

Question 1

Define Incomplete Penetrance

Answer 1

When some people with a disease-causing mutation (change) in a gene develop the disease while others don’t.

Question 2

What are the mechanisms for incomplete penetrance?

Answer 2

Environmental factor
Genetic Modifiers

Question 3

Define genomic imprinting

Answer 3

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.

Question 4

What are the mechanisms for genomic imprinting?

Answer 4

Variants from parents

Question 5

Give an example of extranuclear inheritance.

Answer 5

Mutations in the mitochondria

Question 6

Define Anticipation Inheritance.

Answer 6

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.

Question 7

Define complex inheritance.

Answer 7

Multiple genes working together

Question 8

Define penetrance

Answer 8

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%.

Question 9

Name a disorder which has a high penetrance.

Answer 9

Cystic Fibrosis

Question 10

Is cystic fibrosis dominant or recessive?

Answer 10

Autosomal recessive

Question 11

List some environmental factors which can contribute to cystic fibrosis.

Answer 11

Lifestyle, Diet, Smoke, Alcohol, Drug,
Stress, Air pollution, Chemicals,
Infection, etc.

Question 12

What are genetic modifiers?

Answer 12

Genes that have small quantitative effects on the level of expression of another gene.

Question 13

What are epigenetic modifications

Answer 13

Heritable changes in gene function not explained by changes in DNA sequences

Question 14

What is epigenetic modification mediated by?

Answer 14

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

Question 15

Name some mechanisms which can cause a disorder of imprinting.

Answer 15

Deletions
Point mutations
Imprinting errors

Question 16

What is meant by uniparental disomy?

Answer 16

Where you end up with two copies of one parent’s chromosome.
Inheritance of a chromosome pair from one parental origin

Question 17

What happens if you get deletion of a maternal copy of a gene?

Answer 17

You would end up w no working copy

Question 18

What happens if you have deletion of a parental copy of a gene?

Answer 18

No difference

Question 19

Where do we inherit our mitochondria from?

Answer 19

Mother in egg cells- any mitochondria in the sperm degrades

Question 20

What is the mutation rate of the mitochondria like?

Answer 20

Very high

Question 21

Why does mitochondria have a high mutation rate?

Answer 21

Lack of DNA repair system.
Lack of protective proteins like histones so more exposed to free radicals.

Question 22

Define homoplasmy

Answer 22

When an individual has all the normal copies of their mitochondrial genome.

Question 23

Define Heteroplasmy.

Answer 23

When you have two or more mitochondrial DNA which have an odd genetic alteration or mutation within them.

Question 24

What type of tissues do mitochondrial DNA tend to attack?

Answer 24

Affect tissues with high metabolic demand.

Question 25

Name three major myopathies.

Answer 25

-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

Question 26

Multigenic/complex inheritance is often seen in individuals with?

Answer 26

Heart disease
Breast cancer
Autism