Non-Mendelian Inheritance

Question 1

What is non-mendelian inheritance?

Answer 1

General terms the refers to any pattern of inheritance in which traits do not segregate in accordance with Mendels laws

These laws describe the inheritance of traits linked to single genes on chromosomes in the nucleus

Question 2

What are CNVs?

Answer 2

Copy number variations - extra of missing stretches of DNA - deletions or duplications

Question 3

In CF for example what is the contribution of genetic and environmental factors?

Answer 3

Very little environmental and huge amount of genetic

Question 4

What disease has a 100% penetrance?

Answer 4

Achondroplasia

Question 5

What is penetrance?

Answer 5

Likelihood of having the disease if you have the mutation

Question 6

What is a Mendelian disorder?

Answer 6

One which is controlled by a single locus, mutation in a single gene causes the disease

Question 7

What is a multifactorial disorder?

Answer 7

Does not have a single cause, associated with the effects of multiple genes in combination with lifestyle and environmental factors.

Question 8

Describe penetrance in Mendelian disorders

Answer 8

High penetrance

Small environmental contribution

Question 9

Describe penetrance in multifactorial disease?

Answer 9

A genetic change is just another risk factor

Penetrance for any one mutation is low

Question 10

Heart diseases is more common in _____ degree relative of affected individuals

Answer 10

Heart diseases is more common in first degree relative of affected individuals

Question 11

What percentage of genes do monozygotic and dizygotic twins share?

Answer 11

Mono - 100%

Di - 50%

Question 12

What does P<0.05 mean in a statistical test ?

Answer 12

There is a 1 in 20 probability that the data you see

has happened by chance

Question 13

What is a risk model?

Answer 13

An equation that ties together different risk factors and gives you a risk prediction for your patient

Question 14

Name 3 other non-mendelian inheritance patterns

Answer 14

Epigenetic modification of DNA

Mitochondrial inheritance

Somatic mosaicism

Question 15

What is DNA methylation?

Answer 15

DNA methylation is an epigenetic mechanism used by cells to control gene expression. … DNA methylation refers to the addition of a methyl (CH3) group to the DNA strand itself, often to the fifth carbon atom of a cytosine ring.

Question 16

Describe some more about DNA methylation?

Answer 16

It occurs on the cytosine base just before guanine, usually ending up with methyl CG.
Methylation can effect interactions with histones etc, making DNA now hard (instead of easy) to transcribe

Question 17

What is the clinical importance of DNA methylation?

Answer 17

Abnormalities of methylation causes genetic disease

Methylation causes gene silencing in cancer

Question 18

What is imprinting?

Answer 18

Differences in gene expression depending on whether a gene is maternally or paternally inherited.

Variation in gene expression depending on
which parent you inherit the gene from

Question 19

What happens if the allel from the father is imprinted?

Answer 19

It will be silenced and only the mother allel will be expressed

Question 20

Give some symptoms of Angelman Syndrome?

Answer 20

Neuro genetic disorder 
Developmental delay
Intellectual disability 
Ataxia 
Epilepsy
Happy demeanor
Frequent laughing and smiling

Question 21

Why does angelman syndrome happen?

Answer 21

If you dont have a working cop of the UBE3A gene which is on chromosome 15.
UBE3A only works in the copy you get from your mother.
The copy from your father is methylated

Question 22

Roughly what is Paternal Uniparental Disomy?

Answer 22

When you get both copies of chromosomes from one parent, and one from the other parent, you loose that one, so have both from the one parent. Which have diseases and so you get disease…

Question 23

Where else do you keep DNA?

Answer 23

Mitochondrial DNA

Question 24

Describe Mitochondrial DNA?

Answer 24

Many copies (because of many mitochondria) in a cell
Contains important genes for mitochondrial metabolic pathways and ribosomal RNAs
Inherited almost exclusively maternally
Point mutations and deletions occur

Question 25

What is heteroplasmy?

Answer 25

Different daughter cells contain different proportions of mutant mitochondria

Severity and nature of phenotype depends on
proportion of mitochondria carrying a mutation
level of mutated mitochondria in each tissue
type of mutation

Question 26

Give some symptoms of mitochondrial disease?

Answer 26

Myopathy
Diabetes
Deafness
Optic atrophy
Stroke like episodes
Encephalitis

Dependent on mutation type and level of heteroplasmy in different tissues