Fundamentals 7

Question 1

What are transitions ?

Answer 1

A mutation where a purine base is replaced by another purine (A-G), or a pyrimidine base is replaced by another pyrimidine (G to C)

Question 2

What are transversions ?

Answer 2

Mutations where a purine is substituted by pyrimidine or vice versa

Question 3

Purines

Answer 3

Adenine
Guanine

Question 4

Pyrimidines

Answer 4

Cytosine
Thymine

Question 5

What is epistasis ?

Answer 5

It occurs when one gene controls or influences the expression of another gene

Question 6

What is penetrance ?

Answer 6

The percentage of individuals with a given allele who exhibit the phenotype associated with that allele

Question 7

What does 100% penetrance mean ?

Answer 7

Everyone who has the mutation shows the trait or disease

Question 8

What is incomplete penetrance ?

Answer 8

Some people with the mutation do not show the trait

Question 9

What is expressivity ?

Answer 9

How strongly a trait appears

Question 10

What causes incomplete penetrance ? And variable expressivity ?

Answer 10

1. Interacting genes in the rest of the genome- genes that may act to prevent the expression of the phenotype eg. Uncharacterised modifiers, epistatic genes or suppressors
2. Influence of the environment