5.1 Modes Of Inheritance

Question 1

What is an autosomal dominant condition?

Answer 1

A condition where only one faulty allele is needed for the condition to be expressed

Question 2

Who do autosomal dominant conditions manifest in?

Answer 2

They mainfest in heterozygotes

Question 3

What are the effects of autosomal dominant conditions?

Answer 3

1. Gain of function
2. Insufficient amounts of protein being produced
3. Dominant negative effect

Question 4

What is an example of an autosomal dominant condition?

Answer 4

Huntingtons

Question 5

What type of pedigree pattern do autosomal dominant conditions show?

Answer 5

Vertical pedigree pattern

Question 6

What causes Huntingtons disease?

Answer 6

expansion of a CAG repeat which results in mutant proteins being produced which interfere with the functioning of normal nerve cells

Question 7

What is meant by gain of function?

Answer 7

Gain of function is where the protein becomes hyperactive, and it is this hyperactivity which results in the onset of the disease

Question 8

What is meant by a dominant negative effect?

Answer 8

Where the mutated protein produced interferes with the functioning of the normal protein

Question 9

How is osteogenesis imperfecta a dominant negative disorder?

Answer 9

Type 2, 3, and 4 mutations affect the structure of collagen and interefere with the function of the protein

Results in weakening connective tissue (e.g. bone)

Question 10

How do autosomal dominant conditions effect men and women?

Answer 10

They affect men and women equally

Question 11

What are autosomal recessive conditions?

Answer 11

Where you need two copies of the allele in order for the condition to be expressed

Question 12

What are the usual effects of autosomal recessive conditions?

Answer 12

Loss of function – having both copies results in a completely malfunctioning protein

Question 13

How is cystic fibrosis an example of an autosomal recessive condition?

Answer 13

Mutation to CTFR gene encoding chloride ion channels results in defective channels

This results in mucus buildup, impaired airway defense, digestive issues, thus is a loss of function mutation

Question 14

What type of pedigree pattern do autosomal recessive conditions show?

Answer 14

Horizontal pedigree

Question 15

What can increase the risk of autosomal recessive conditions?

Answer 15

Consangious marriages

Question 16

Why can autosomal recessive conditions skip generations?

Answer 16

Due to the high chance of being a carrier

Question 17

How are men and women affected with autosomal recessive conditions?

Answer 17

They are affected equally

Question 18

What type of chromosomes are autosomal recessive genes located on?

Answer 18

Non-sex chromosomes

Question 19

What percentage of DNA is shared between first cousins?

Answer 19

12.5%

Question 20

Who do X-linked recessive conditions mainly affect?

Answer 20

Men

Question 21

How can females have an X linked recessive condition?

Answer 21

They have to be homozygous for the condition

Question 22

Why are X-linked dominant conditions often milder and more variable in females than males?

Answer 22

Due to random X inactivation

Thus some females have X chromsome with normal rather than mutant gene

Question 23

What is usually an effect of X-linked dominant disorders?

Answer 23

Increase in function

Question 24

How is X-linked hypophosphatemia an increase in function disorder?

Answer 24

Mutation in the PHEX gene causes overproduction of FGF21 protein

FGF21 inhibits kidney phosphate reabsorption, leading to vit D resistance and rickets

Question 25

What is the chance of a daughter of an affected male being a carrier of an X linked recessive condition?

Answer 25

100%

Question 26

What is an X linked recessive condition?

Answer 26

Where the alleles are located on the sex chromosomes

Since males have XY, they have an increased risk of the condition as if they only need the one recessive allele to have the condition

Question 27

What happens to the daughters and sons of an affected father and unaffected mother of an X linked dominant condition?

Answer 27

Daughters all affected

None of sons affected

Question 28

Who do Y linked disorders affect?

Answer 28

Only men as females do not have Y chromosome

Question 29

What type of pedigree pattern do Y linked disorders show?

Answer 29

Vertical patern with only males affected

Question 30

Who are all your mitochondria inherited from?

Answer 30

Mother

Question 31

A mother has a mitochondrial condition. What happens to her children?

Answer 31

They are all affected

Question 32

What is heteroplasmy?

Answer 32

Mitochondria have multiple copies of their genome, some mutant and some normal

Symptoms only occur if the number of mutant genes exceeds a threshold

Question 33

Why do the expression of mitochondrial conditions vary massively in a family?

Answer 33

When the mitochondria replicate, genes can be lost or gained meaning there is an enourmous amount of variation

Question 34

Why are mitochondrial diseases hard to diagnose?

Answer 34

Motor and nerve function are affected

Present as unrelated multi-system symptoms

Question 35

What type of inheritance is it when children of unaffected parents are affected?

Answer 35

X linked recessive

Question 36

What type of inheritance is it when all children of an affected mother are affected?

Answer 36

Mitochondrial

Question 37

Why do mitochondrial diseases develop with age?

Answer 37

Accumulation of mutant mitochondria

Also, different tissues contain different numbers of mutant mitochondria and this can change with time