Download
1 / 9
100 likes | 252 Vues
Insertion mutations occur when DNA bases or fragments are added to a sequence, sometimes due to inaccurate copying or through larger DNA movements like transposable elements. Notably researched by Barbara McClintock, whose work on "jumping genes" revealed that approximately 65% of the human genome consists of these elements. Viruses also contribute to this by integrating their DNA into host genomes, which can disrupt gene function, leading to diseases like cancer. However, some viral insertions may offer benefits, such as activating beneficial genes or aiding in gene therapy.
E N D
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
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
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
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
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
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. • Bornavirusschizophrenia and other mood disorders. • Herpes virus 1 Alzheimer’s
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)
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.
