Mick Genetics Flashcards
A boy has an apparently de novo mutation leading to Duchenne muscular dystrophy. (Mother is completely asymptomatic clinically and biochemically)
However, when she sees a geneticist, they say that her risk of another boy with DMD is slightly higher than the background population risk
Why is this?
This relates to a condition called gonadal mosaicism.
When cells are multiplying, there is a risk that one of these cells will have a mutation (such as DMD). If, for example, there are currently 128 cells, and just one of them has this mutation, eventually this will lead to ~1% of that person’s cells having DMD mutation (possibly only 1 allele too!)
If, rather unfortunately, those mutated cells are the ones selected out for reproduction, then that could account for an “apparent de novo mutation”
We don’t have a good way to test the mother for this MOSAICISM
Therefore we have to tell the mum that her risk of another DMD is slightly higher than background risk. But it could be that her son does truly have a de novo mutation.
The only test would be pre-natal testing, but at that stage, the child is already on the way.
Overall, it is more likely that the mother has gonadal mosaicism than have 2 children with a de novo mutation.
What is the genetics that is associated with the most common CF gene?
overall it is a deletion of an entire amino acid from the downstream protein. There is a deletion of 3 codons.
DeltaF508 means deletion of F (phenylalanine) 508
This is actually deletion of CTT from the DNA at position 1521-1523
An Array comparative genomic hybridization (aCGH) study is a super clever way of detecting presence of parts of chromosomes. Basically they cut the chromosomes up (during metaphase) and then compare those to a NORMAL control. If there is decreased of a section, it will be seen. If there is more, it will be seen.
What won’t it see?
It won’t see a balanced translocation
what is the definition of gene frequency?
What is the definition of carrier frequency?
Carrier frequency is the frequency of carriers
For example, 2 of 10 people are carriers. This is 20%
c.f. gene frequency is the frequency of the gene allele.
If 2 of 10 are carriers, this means that 2 of 20 genes are abnormal. This is 10%
what are the genetics of DMD and how does it come to be? (what is the abnormality about its dodgy genes?)
it is x-linked recessive
it is a problem with the dystrophin gene.
the commonest way that this comes about is deletion of several exons in this protein.
multiple other processes can cause problems with this protein, but above is most common
