Lecture 8. Mutations reveal the anatomy and function of a gene.

I. Importance

Mutations provide the initial variation for selection and are very important in evolution

mutations are used by biologists to understand many biological processes at the molecular level

II. Types of mutations and definition and Rates

Mutations- heritable changes in DNA base sequence

Types: Forward; Reverse or reversion (mutant back to wild type)- much lower frequency than forward

III. Mutations: Random or Induced

Observation: Spread bacteria on a plate with antibiotic and some colonies will form.

Did the antibiotic induce the mutation OR Was the mutation in a bacteria before, thus a random occurrence??

Two Experiments: Luria-Delbruck fluctuation expt, Lederberg’s replica plate expt.

IV. Agents of mutation

Environmental Agents: Hydrolysis, Radiation, Ultraviolet light, Oxidation

DNA Replication

Unequal Crossovers lead to mutations

Transposition

V. DNA Repair Systems

Methylation allows repair enzymes to recognize the original strand

VI. Detecting lethal mutations

Using segregation of a marked X chromosome can allow detection of lethal mutations

VII. Mutations Reveal Gene Structure

Complementation Reveals if 2 mutations are in same gene

IX. Conclusion

The mutation rate for a given locus is small

The vast majority of mutations are harmful

But

With lots of individuals in a species and lots of genes that can mutate, some small but finite amount of

mutations will be beneficial

Mutations have large consequences on conservation biology and evolution of organisms, as well as on

human medicine

Terms to Know: Mutation, reverse, forward, Luria-Del. fluctuation test, Lederbergs replica plating, random

nature of mutations, Unequal x-over, Methylation DNA repair system, Benzer’s expt., cistron,

complementation group, evidence that genes code for enzymes

Figs: 2, 3, 4, 5, 8, 9, 10, 13, 14, 15, 16, 18, 23, 25, 27, and Fig A on page 221