Lecture, chapter 13 - Mutation

Child with xeroderma pigmentosum a disorder caused by mutations
on genes involved in DNA repair mechanisms
_____________________________________________________

Today we finished the chapter on mutation.

We talked about how insertions and deletions (indels) can affect a nucleotidic sequence depending on how many nucleotides are inserted and whether or not they change the reading frame of the sequence.

Then we discussed the basics of the proofreading and DNA repair mechanisms that cells have in place to fix DNA changes, which happen at a much greater rate than the rate of mutation (reminder: a mutation is a DNA change that gets passed to subsequent generations of cells and/or organisms; it's a DNA change that doesn't get repaired).

We also considered a third category of mutations: allelic expansions, which interestingly enough happen in only one of the alleles in a gene pair. Genes that have trinucleotide repeats undergo mutations in which the number of repeats increase to the point in which the protein they encode for is not functional any more.
We mentioned anticipation, the phenomenon in which a genetic disorder caused by an allelic expansion is expressed in a more severe way, and at earlier ages, generation after generation.

----------------------