Insertion Mutations

1. Insertion Mutations

2. What is an insertion mutation? • Mutations caused by the insertion of DNA bases or fragments • This can happen when DNA is copied incorrectly (frameshift mutation) • One or two bases are added • This can also happen when large fragments move from one place to another

3. Barbara McClintock • Genes and chromosomes were originally described as “beads on a string”; it was thought that genes occupied a fixed position on a chromosome • Barbara McClintock received a Nobel prize in 1983 for her workdiscovering transposable elements or “jumping genes”: DNA fragments that can move from one chromosome to another. • Today we know that 65% of the human genome is composed of transposable elements

4. McClintock’s Observations: • McClintock discovered transposons by studying colour pattern in Indian corn • She found that corn kernels which should have been brown or purple according to their genotype, would often show patches of white • She correctly predicted that this happened if a transposon inserted itself and disrupted the pigment producing gene. • Also seen in hosta plants

5. Viruses • Viruses contain genetic information, but are not living things. • In order to make copies of themselves, they rely on cell machinery of the host • Viruses insert their DNA into the host’s genome, so the host will transcribe and translate viral genes in order to make viral proteins

6. Viruses • Throughout evolution, our DNA has acquired many relics of past viral infection. • Once the human genome was sequenced in 2000, it was found that ~ 8% of our genome is from viruses! • Like transposons, when viral DNA is inserted in the middle of a human gene, its function will be disrupted. • Viral insertions usually occur in regulatory genes, which increase or decrease the function of another gene

7. Negative effects of viral insertions • Insertions can be harmful • If viral genes disrupt genes that regulate cell growth, infection may cause cancer = oncovirus • HPV (Human Papilloma Virus) • Hepatitis C Virus • Prior infection with certain viruses has been linked to the development of other diseases. • Bornavirusschizophrenia and other mood disorders. • Herpes virus 1 Alzheimer’s

8. Benefits of viral insertions • Insertions can be beneficial • Viral insertions have activated some digestive enzymes in human saliva by disrupting suppressor genes • Infection by less harmful virus prevents infection by more dangerous strains. • Vaccinia prevents small pox • Viral machinery can be manipulated to insert helpful genes into cells (gene therapy)

9. Genetics and Probability Homework • 0.50 that 1st child will be brown-eyed (depends on inheriting B from dad: Bb) 2. a) 0.25 (both are HRHW, 0.50 that each pass on HR allele) b) 0.50 ( 0.25 probability of each combination, 2 combinations produce roan cattle) • a) cross 1: 0.50; cross 2: 0.00; cross 3: 0.25 b) cross 1: 0.50; cross 2: 0.50; cross 3: 0.50 c) cross 1: 0.00; cross 2: 0.50; cross 3: 0.25 • a) affected son: 0.50 affected daughter: 0.00 b) affected son: 0.25 (50% mom is a carrier x 50% she will pass on alllele); affected daughter: 0.25 • man: Rr bb woman: rr BB a) left handed child: 0.50 b) left handed with brown eyes: 0.50 (probability of brown eyes is 1.00) 6. Condition is recessive; 0.50 that carrier female will pass on affected allele, 0.67 that man is a carrier, 0.50 that man will pass on affected allele 0.50 x 0.67 x 0.50 = ~ 0.18 that they will have an affected child.