Typical/Atypical Mendelian Inheritance

Question 1

What is the pedigree pattern of AD disorders?

Answer 1

Vertical

Question 2

What causes variable expressivity of AD disorders?

Answer 2

Modifier genetic variants (e.g. FGFR2 variants in BRCA2 mutations)

Question 3

What is incomplete penetrance?

Answer 3

Absence of condition despite being inherited autosomal dominantly

Question 4

What are some AD conditions?

Answer 4

Achondroplasia
Familial breast/colon cancer
AD polycystic kidney disease
NF1

Question 5

What is the pedigree pattern of AR conditions?

Answer 5

Horizontal

Question 6

What is consanguinity?

Answer 6

When mum and dad are related by blood - important to consider in AR conditions

Question 7

How do AD and AR conditions distribute across males and females?

Answer 7

EQUAL frequency and severity

Question 8

Can X-linked conditions show male-male transmission?

Answer 8

No - males will only ever receive Y chromosome from their father

Question 9

In x-linked recessive what is “knights move”?

Answer 9

No male-male transmission but mostly/only males affected

Question 10

Are females affected by x-linked recessive conditions?

Answer 10

Unlikely, but if affected then more mildly

Question 11

What can cause “manifesting carriers” in females?

Answer 11

Scewed x-inactivation

Question 12

What is an example of an x-linked recessive condition?

Answer 12

Duchenne muscular dystrophy

Question 13

What is the sex ratio in x-linked recessive?

Answer 13

M&raquo_space; F

Question 14

What is the pedigree pattern of x-linked dominant?

Answer 14

Vertical

Question 15

What is the sex ratio in x-linked dominant?

Answer 15

2 female : 1 male

Question 16

What are examples of x-linked dominant conditions?

Answer 16

Vit D resistant rickets

male lethality =
Incontinentia pigmenti
Rett syndrome

Question 17

What is genetic anticipation?

Answer 17

Increasing severity and decreasing age of onset in successive generations

Question 18

Which conditions show genetic anticipation?

Answer 18

Huntington’s disease
Fragile X syndrome
Myotonic dystrophy

Question 19

What is gonadal mosaicism?

Answer 19

Mutation might be in more than one egg or sperm cell in parent’s gonads

Question 20

What is pseudo-dominant inheritance?

Answer 20

High carrier frequency or consanguinity makes a true AR condition appear AD (e.g. Gilbert syndrome)

Question 21

Which parent can pass on mitochondrial DNA mutations?

Answer 21

Mother