April 20 Notes

1.) Molecular basis of mutations
a.) Nucleotide substitution: Replacement of 1 base in DNA sequence with new base.
b.) Frameshift mutations: Addition/Deletion of non 3x the number of bases from coding region of a gene.
C.) Expansion of trinucleotide repeats: An increase: Repitition of nucleotide sequence within a gene.
i.) Ex: Increase in sloped nose of Bull Terriers
ii.) Why? Even though there is little genetic diversity it is very easy for mutations to occur. Also, it is still complementary base pairing, so during replication it does not recognize it as a mutation.
iii.) Ex: Fragile X-Syndrome: If you have 6-50 copies it is normal. If you have 50-230 copies you are fine, but your children will have fragile x symptoms. If you have more than 230 copies, then you have fragile x syndrome. This is because you have more copies of CGG repeats (230 copies), so lots of CGG's causes the protein to not be expressed because of the methylation of the x chromosome. (CpG motifs, C+G are most likely to be methylated).
It is most common because it may not be recognize as a mutation. (fig. 14-8, page 518)
2.) Spontaneous mutations: Occur on their own; not caused by an event.
a.) Mutations are non-adaptive: Ex: 2 copies of mutant B-globin at codon 6 you have valine instead of wild type glutamine (this is sickle cell anemia). But, if you have one copy of mutant B-globin gene, you do not have sickle cell anemia and your resistant to malaria. However, adaptive mutations persist in a population because individuals with the adaptive mutations are not killed off as much as individuals without the adaptive mutations.
b.) Mutational hotspots: areas in DNA more prone to mutation than others
ex: repetitive sequences:slipped-strand mispairing and stretches w/ lots of T's (or lots pyrimidines in general) UV light can cross-link 2 or more adjacent thymines

2.) Mutagens: Thing that causes DNA sequence changes(=mutations)

a.) Depurination via hydrolysis (Water purines easily removed from sugar phosphate backbone via hydrolysis)

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