Transcript Mutations
Mutations The ultimate source of new alleles Changes to the DNA Sequence • Entire set of DNA is copied each time a cell divides. • Copying process may not be error free. • Chance that a base or series of bases is either copied incorrectly, deleted, reversed or inserted as an addition. • Low normal error rate – about one mistake per billion base pairs copied. Think about this error rate! • Approx. 3 billion base pairs in human genome (meaning, 3 billion base pairs in each somatic cell) • Keeping this error rate in mind, how many errors should you expect each time one of your cells divides? • (1016 cell divisions in a lifetime!!!) • How many mutations should you expect in a lifetime? In a day? Mutation as source of genetic variation • A large percentage of DNA codes for nothing! Mutations in these sections do not lead to variation. • Generally, mutations are kept in check by the DNA repair system. Mutated cells are often either fixed or destroyed! • Mutations in somatic cells are not carried forward to the next generations. • Only mutations in sex cells can be passed down from parent to offspring and further on. Harmful mutations • Most mutations in genes (parts of DNA that code for proteins) are harmful. • Usually stop or alter production of a protein. • This causes the protein to malfunction. • E.g. albinism, thalassemia, Silent mutations • Cause no changes in amino acid sequence or final protein product. • This may be because: - mutation occurs outside gene region - codon change was for the same amino acid - minor change in amino acid sequence may not have altered the shape or active site of the protein. Beneficial Mutations • Sometimes mutations improve the survival chances of organism. • Most common example is of flu virus – frequent mutations leading to changes in its glycoprotein “coat” (outer covering) helps it avoid detection by the host’s immune system. • MRSA – hospital super bug! • Mutations passed down through gametes, if beneficial, continue to persist in a population. Mutagens – agents that speed up the normal rate of mutation • Radiation – nuclear, UV, X-rays • Diet, Alcohol, Tobacco smoke – diets high in saturated fat, MSG, high alcohol intake, tobacco tar – irritants that induce cancer causing mutations • Chemicals – asbestos, alcohol-based solvents like paint thinners and formaldehyde, and many many others… • Microorganisms – HIV, HPV, Hepatitis B virus, aflatoxin produced by a fungus commonly growing on peanuts.