What does molecular genetics look for?
Molecular genetic change that explains disease. Typically DNA based testing
Explain Sanger sequencing
- 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
If a mutation is recessive, what is the likely outcome for the protein?
Reduced, or no function
Mutation is usually nonsense, missense, frameshift or a splicing variant
If a mutation is dominant, what is the likely outcome for the resulting protein?
New, abnormal function, unless dominant negative
Mutation is usually missense
What is a synonymous molecular change?
No change to the protein, but changes in binding sites for enhancer or suppressor proteins
What is a dynamic mutation, and which two disease have this?
An increase or decrease in naturally occurring repetitive sequences of codons.
Disorders include Huntingtons and fragile X
What is a disorder of imprinting?
What does p.Ala479Pro describe?
Alanine was the original amino acid, that was changed to a proline, at codon position 479 in the reference sequence
What does p.[(Tyr63*)]; mean?
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  represents that this must have occurred on an X chromosome, and the subject is a man
In which two scenarios can a mutation appear homozygous, when it’s actually not?
- X-linked disorder in a man
- A gene has been deleted from the other chromosome