Genetic Principles

Question 1

Give examples of typical mendelian inheritance mechanisms

Answer 1

Autosomal dominant
Autosomal Recessive
X linked

Question 2

What patterns would you be able to see on a pedigree for a genetic condition with autosomal dominant inheritance?

Answer 2

Vertical pattern of inheritance
Both males and females affected
Possible for it to be passed from father to son

Question 3

By looking at the patterns on a pedigree, how can an autosomal dominant condition be differentiated from an x linked condition?

Answer 3

In AD it is possibe for the condition to be passed from father to son

Question 4

Autosomal dominant conditions can have variable expressivity. What does this mean?

Answer 4

That within a family people may have the same genetic alteration buy can have the disease to different extents

Question 5

Some autosomal dominant conditions exhibit complete penetrance. What does this mean?

Answer 5

That if the mutation is inherited then the individual will definitely develop the disease

Question 6

Some autosomal dominant conditions exhibit incomplete penetrance. What does this mean?

Answer 6

That if if the mutation is inherited then the individual may not go on to develop the disease at all

Question 7

Give an example of an autosomal condition which has complete penetrance?

Answer 7

Huntington’s disease

Question 8

In addition to to the mutated genes of the autosomal dominant condition itself, what other genes can affect the severity and/or penetrance of the condition?

Answer 8

Modifier genes

Question 9

Give examples of autosomal dominant conditions

Answer 9

Inherited breast or colon cancer
Polycystic kidney disease
Huntington’s disease
Neurofibromatosis type 1

Question 10

What is meant by the term ‘compound heterozygote’?

Answer 10

The individual has two different mutations in the same gene resulting in the disease

Question 11

What is meant by the term ‘double heterozygote’?

Answer 11

The same fault or mutation is present in more than one gene within an individual

Question 12

In autosomal recessive inheritance, if you see an affected child then you should assume that the parents are carriers. T/F?

Answer 12

True

Question 13

What is the term for an individual who has inherited only one faulty copy of a gene for an autosomal recessive condition?

Answer 13

Carrier

Question 14

What is meant by the term ‘consanguinity’?

Answer 14

The parents are related e.g. the parents are cousins

Question 15

Give examples of autosomal recessive conditions.

Answer 15

Cystic fibrosis
Phenylketonuria
Spinal muscular atrophy
Congenital adrenal hyperplasia

Question 16

There is often variable expressivity of autosomal dominant conditions. Is this also true for autosomal recessive conditions?

Answer 16

No - expressivity is more constant within a family for AR conditions

Question 17

What type of inheritance mechanism exhibits a horizontal pedigree pattern?

Answer 17

Autosomal recessive

Question 18

What patterns would you be able to see on a pedigree for a genetic condition with x linked recessive inheritance?

Answer 18

Knight’s move pattern
No male to male transmission
Mostly or only males are affected

Question 19

Explain the mechanism of skewed X inactivation by which females can be mildly affected by X linked recessive conditions.

Answer 19

In the early embryo, within each cell, one of the X chromosomes in inactivated or switched off. Therefore, in female carriers of an X linked recessive condition, if in the majority of cells the damaged allele is randomly selected to remain switched on then the individual can be mildly affected by the disease

Question 20

What is the term for females in a family who are mildly affected by X linked recessive conditions due to skewed x inactivation?

Answer 20

Manifesting carrier

Question 21

Give an example of an X linked recessive condition

Answer 21

Duchenne’s muscular dystrophy

Question 22

Give examples of X linked dominant conditions

Answer 22

Vitamin D resistant rickets
Incontentia Pigmentia
Rett syndrome

Question 23

Incontentia pigmentia and rett syndrome are X linked dominant conditions which are lethal in males. T/F?

Answer 23

True

Question 24

There is a vertical pattern of inheritance for X linked dominant conditions. T/F?

Answer 24

True

Question 25

If a male with an X linked recessive condition has a daughter, then this daughter will be affected by the disease. T/F?

Answer 25

False - this would be true of an X linked dominant condition but in an x linked recessive condition the daughter of an affected male would be an obligate carrier

Question 26

More men than women in a family are likely to be affected by an x-linked dominant condition. T/F?

Answer 26

False - there is usually a 2:1 ratio of women:men affected by an x-linked dominant condition in a family

Question 27

What term describes the increasing severity and earlier age of onset in successive generations exhibited in some genetic conditions?

Answer 27

Genetic anticipation

Question 28

Give examples of conditions which exhibit genetic anticipation.

Answer 28

Huntington’s disease
Fragile x syndrome
Myotonic dystrophy

Question 29

Which genetic condition is caused by a CAG repeat which expands in subsequent generations?

Answer 29

Huntington’s disease

Question 30

What is pseudo-dominant inheritance?

Answer 30

A type of autosomal recessive inheritance where, because of the condition’s high carrier frequency or because o consanguinity, it appears as autosomal dominant inheritance

Question 31

Give an example of a pseudo-dominant condition?

Answer 31

Gilbert’s syndrome

Question 32

How does mitochondrial DNA differ from nuclear DNA?

Answer 32

Mitochondrial genome is much smaller
Circular DNA
No introns

Question 33

Mitochondrial DNA is only inherited from which parent?

Answer 33

The mother

Question 34

Mutations affected the mitochondria DNA of the mother have what percentage chance of being passed on to the children?

Answer 34

100%

Question 35

Mutations affected the mitochondria DNA of the father have what percentage chance of being passed on to the children?

Answer 35

0%

Question 36

Since mutations affecting the mitochondria DNA of the mother have a 100% chance of being passed on to the children, will all the children be affected by the disease?

Answer 36

Not necessarily since the severity of the resulting condition is variable

Question 37

What tissues do mitochondrial genetic conditions typically affect?

Answer 37

Brain
Muscles
Eyes

Question 38

What is meant by the term ‘heteroplasmy’ and what gives rise to this?

Answer 38

The presence of more than one type of organellar genome because of the fact that not every mitochondria within a cell might be affected by a mutation