Mutations

1. Mutations • These are errors made in the DNA sequence that are inherited. • These may have negative side effects, no side effects or positive side effects.

2. Negative side-effects • Some mutations may lead to a the development of a disease. • Cystic fibrosis – mutation in the cystic fibrosis transmembrane regulator

3. Positive Mutations • The human brain occurred through mutation. • Caused a natural selection and the larger brains prevailed.

4. No effect • The side effect may not surface immediately – especially eukaryotes • We are diploid organisms meaning that we cancel the mutations out. • If humans were haploid in nature much of the world population would be gone as we carry so many mutations.

5. Types of Mutations • Silent mutations • No effect on the operation of the cell • Usually occurs in the introns of DNA • This means that post-transcription modification removes this mutation

6. Mutation can also be silenced through the redundant nature of the genetic code. • Eg. Phenylalanine – UUU, UUC on mRNA • Mistakes made during transcription or if a mutation is made and the third base is replaced with a G instead of an A – phenylalanine will still be created.

7. Missense mutation • A mutation that results in the single substitution of one amino acid in the resulting polypeptide • Change in the base sequence of DNA alters a codon – leading to a different amino acid in the sequence. • Sickle cell anemia

8. Normal red blood cell • Round flexible able to pass through tiny blood vessels.

9. Sickle cell • Looses flexibility • Is rigid and blocks blood vessesls depriving the area of blood supply

10. Nonsense mutations • Mutation that converts a codon for an amino acid into a termination codon. • During translation only part of the protein will be created and the fragment may be digested by proteases. • Often lethal to the cell

11. Substitution and Deletion • Missense and nonsense mutations occur because of substitutions or deletions of a base pair. • Substitution – replacement of one base in a DNA sequence by another base • Deletion – the elimination of a base pair or group of base pairs for a DNA sequence. • Point mutations – if only one base pair.

12. By removing a base pair, it results in different base pairs being read. • This will cause a drastic change in protein structure.

13. Insertion • The placement of an extra nucleotide in a DNA sequence. • Because DNA is read in triplets of nucleotides, and will cause different amino acids.

14. Frameshift Mutations • Causes the reading frame of codons to change • This results in different amino acids being incorporated into the polypeptide. • Insertion and deletion can be considered Frameshift mutations, if they result in less than three codons being shifted. • 3 nucleotides can be less serious.

15. Translocation • The transfer of a fragment of DNA from one site in the genome to another location. • A segment of a chromosome breaks and releases a fragment – this happens as the same thing is happening to another chromosome. • The two fragments switch places – disrupting normal gene structure.

16. This new segment can be transcribed and translated. • New protein with an altered function. • Some leukemia are a result of this.

18. Transposable Elements • Segments of DNA that are replicated as a unit from one location to another on chromosomal DNA • They move from one location to another, making genes inactive. • Various colours of Indian corn are a result of Transposable genes - McClintock

19. Could this happen???

20. Inversion • Reversed its orientation in the chromosome • No gain or loss of genetic material. • Some genes may be disrupted.