Mutations

1. Mutations

2. Sequence • We have seen that the order of nucleotides dictates the amino acid expressed • If a single base pair is changed in the genetic code, a different amino acid can result • This is called a point mutation • There are two types: substitutions and insertions or deletions

3. Substitutions • A nucleotide and its complement get replaced by another pair • Often this is a silent mutation – occurs on an intron, or does not change amino acid expressed • For example, if coding strand is changed from CGC to CGT, mRNA changes from CGC to CGU • Both codons yield an arginine

4. If the mutation does change the amino acid, it is usually a missense mutation • Makes sense, but not the right sense • One of the most commonly cited examples of this is sickle-cell disease

8. In rare cases, it can change to a stop codon, leading to a premature termination of the protein • This is a nonsense mutation

10. Insertions and Deletions • Involves addition or loss of one or more nucleotides • Called a frameshift mutation • Can be more of an issue than substitutions as is changes the reading frame • Consider the sentence: “THE CAT ATE THE RAT” • Delete “A” of CAT: • THE CTA TET HER AT

12. Chromosome Structure • It is also possible to change entire segments of a chromosome • There are four types: deletion, duplication, inversion, and translocation

13. Deletion • Fragment of chromosome lost during replication

14. Duplication • When the piece broken off in a deletion reattaches to a homologous chromosome

15. Inversion • When the fragment reattaches to original chromosome, but has “flipped”

16. Translocation • Segment reattaches to a nonhomologous chromosome