Genetic Principles

Question 1

What are the typical features of autosomal dominant inherited conditions?

Answer 1

• Variable expressivity
• Varied Penetrance
• Genetic anticipation

Question 2

Describe variable expressivity

Answer 2

Presents differently in affected individuals, those who are homozygous more severely affected

Question 3

Describe incomplete penetrance

Answer 3

Not everyone who receives the mutant allele is affected - but they cam pass it on

Question 4

Describe genetic anticipation

Answer 4

With successive generations, some conditions show a decreasing age of onset and an increasing severity. Seen in neurological conditions.

Question 5

What are some typical features of autosomal recessive conditions?

Answer 5

• More constant expressivity (onset and severity) alone those affected
• Parental consanguity (blood relation) increases the risk of inheritance

Question 6

What is the typical features of X-linked recessive inheritance?

Answer 6

• Males seriously affected

- Only homozygous females seriously affected

Question 7

What are the typical feature of X-linked recessive inheritance?

Answer 7

• Females affected 2x more than males

- Male lethality so many only affect females

Question 8

What is genetic mocaism?

Answer 8

When a mutation occurs after fertilisation, affecting only 1 cell line. Genetic mocaism in the gonads can produce seemingly new mutations.

Question 9

What is pseudoautosomal inheritance?

Answer 9

Traits encoded for at the autosomal regions of the X and Y chromosome, which are inherited in an autosomal (non X-linked fashion)

Question 10

What is pseudo-dominant inheritance?

Answer 10

When an autosomal recessive condition shows a vertical pattern of inheritance, usually due to high carrier frequency.
- e.g. Gilbert Syndrome