Gene and Chromosomal Mutations

1. Gene and Chromosomal Mutations

2. What is a mutation? • Mutations are changes made to an organism’s genetic material. • These changes may be due to errors in replication, errors during transcription , radiation, viruses and many other things. • Mutations can occur within a specific gene (small scale), as well as to the chromosome as a whole (large scale).

3. Are mutations always bad? • Favorable mutations present organisms with an advantage over others and ensure their survival. These mutations will accumulate in a population. • Less favorable mutations are removed from the gene pool through natural selection. • Organisms with these mutations will not survive.

4. Mutations Small Scale Mutations Large Scale Mutations

5. Small Scale Mutations:Gene Mutations • There are three main types of small scale gene mutations. These all affect one nucleotide in a DNA triplet. (Point Mutations) • Reversal/ Substitution (Lucky or unlucky) • Deletions (Frame shift mutations) • Insertions (Frame shift mutations)

6. Small Scale • Point mutations occur when a single nucleotide in a gene is exchanged for another nucleotide. • For example, an A could be exchanged for a T or a C could be exchanged for a G. • These mutations have an effect on protein synthesis. One DNA triplet is altered, which can affect one or more codons and therefore one or more amino acids. • Can be a reversal or substitution

7. Deletions • Deletions are when one or more nucleotides are removed from the DNA sequence. • As with insertions, this causes a shift in the reading sequence of DNA and can produce a completely different protein strand than the original. • Deletions result in Frameshift Mutations

8. Insertions • Insertions occur when one or more new nucleotides are inserted into the DNA sequence. • When this occurs, there is a shift in the reading sequence of DNA during protein synthesis and a completely different protein strand may be formed. • Frameshift

9. Video Animation • http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter11/animation_quiz_4.html • Frame Shift Mutations

10. Large Scale Mutations:Affect large sections of a chromosome • There are three major chromosomal mutations that can occur: • Duplications • Inversions • Deletions

11. Duplication (LSM) • Duplication occurs when a segment of a chromosome is doubled. • The segment of DNA that is doubled may contain many genes. • What affect would this have on the protein?

12. Inversions (LSM) • Inversions occur when a piece of DNA is removed from the chromosome, inverted, and then placed back into the chromosome. • When it is re-inserted, the genes are in reverse order. • What affect would this have on the protein?

13. Deletions (LSM) • Deletions occur when a whole chunk of the chromosome goes missing. • Breaks in chromosomes can be caused by radiation, heat, viruses, chemicals, and other environmental causes. • Consequences of these mutations will depend on what part of the chromosome has been deleted.

14. Deletions • Examples of disorders caused by deletions: • Prader-Willi Syndrome • Deletion of the long arm on chromosome 15 • Characterized by compulsive eating

15. Deletions • Cri-du-chat syndrome • Deletion of the short arm of chromosome 5