Week 8 Genetics - molecular testing

Question 1

What does molecular genetics look for?

Answer 1

Molecular genetic change that explains disease. Typically DNA based testing

Question 2

Explain Sanger sequencing

Answer 2

• DNA polymerases copy single stranded DA templates by adding nucleotides to a growing chain
• DNA Polymerases can also incorporate analogues of nucleotide bases. Sanger sequencing uses 2,3-dideoxynucleotides as substrates, which may be fluorescently labelled. When these are incorporated at the 3’ end of the growing chain, chain elongation is terminated selectively at A, C, G or T - this is because once the deoxynucleotide is incorporated, there is no 3’-hydroxyl group, preventing further elongation
• The resulting fragments are then put together to reveal the sequence of the original piece of DNA
• The fluorescent ddNTPs can then be run through capillary electrophoresis, which output data as coloured peaks, depicting the DNA sequence

Question 3

If a mutation is recessive, what is the likely outcome for the protein?

Answer 3

Reduced, or no function

Mutation is usually nonsense, missense, frameshift or a splicing variant

Question 4

If a mutation is dominant, what is the likely outcome for the resulting protein?

Answer 4

New, abnormal function, unless dominant negative

Mutation is usually missense

Question 5

What is a synonymous molecular change?

Answer 5

No change to the protein, but changes in binding sites for enhancer or suppressor proteins

Question 6

What is a dynamic mutation, and which two disease have this?

Answer 6

An increase or decrease in naturally occurring repetitive sequences of codons.
Disorders include Huntingtons and fragile X

Question 7

What is a disorder of imprinting?

Answer 7

Prader-Willi

Question 8

What does p.Ala479Pro describe?

Answer 8

Alanine was the original amino acid, that was changed to a proline, at codon position 479 in the reference sequence

Question 9

What does p.[(Tyr63*)];[0] mean?

Answer 9

At codon position 63 of the reference sequence, the codon for a Tyrosine has been changed to a stop codon - this is represented by the star.
The [0] represents that this must have occurred on an X chromosome, and the subject is a man

Question 10

In which two scenarios can a mutation appear homozygous, when it’s actually not?

Answer 10

• X-linked disorder in a man

- A gene has been deleted from the other chromosome