Brief Development Example

First Draft Outline as Received from Author

Introduction

Mutation

Mutations are random events

Mutations can involve small changes in DNA sequence, alterations in chromosome structure, or changes in chromosome number

Experiment 17A: X-rays were the first environmental agent shown to cause mutations.

A variety of agents can cause mutations
Mutagens alter DNA structure in different ways

The mutation rate is a measure of new mutations per cell generation

Testing methods can determine if an agent is a mutagen

Certain viruses have unusually high rates of mutation

Trinucleotide repeat expansion is a mutational mechanism that causes certain human genetic diseases

Consequences of Mutation

Gene mutations can alter the coding sequence within a gene

Gene mutations can occur outside of the coding sequence and still influence gene expression

Changes in chromosome structure can affect the expression of a gene
Mutations can occur in the germ line or in somatic cells

In Vitro Site-Directed Mutagenesis

DNA Repair

Experiment 17B: Direct evidence for DNA repair was obtained in studies showing that thymine dimers can be "excised" from DNA

Damaged bases can be directly repaired

The excision of damaged DNA is an important mechanism to repair DNA

Newly replicated DNA can be repaired by a mismatch repair mechanism

Damaged DNA can be repaired by recombination

Actively transcribed DNA is repaired more efficiently than nontranscribed DNA

Conceptual Summary

Final Developed Outline

Consequences of Mutation

Gene mutations are molecular changes in the DNA sequence of a gene

Gene mutations can alter the coding sequence within a gene

Gene mutations are given names that describe how they affect the wild-type genotype and phenotype

Gene mutations can occur outside of the coding sequence and still influence gene expression

DNA sequences known as trinucleotide repeats may cause mutation

Changes in chromosome structure can affect the expression of a gene

Mutations can occur in germ line or somatic cells

Occurrence and Causes of Mutation

Spontaneous mutations are random events

Randomly occurring mutations can give an organism a survival advantage

The mutation rate is a measure of new mutations per generation; the mutation frequency is the relative occurrence of a mutation within a population

Experiment 17A: X-rays were the first environmental agent shown to cause induced mutations, by Muller in 1927

Mutagens alter DNA structure in different ways

Testing methods can determine if an agent is a mutagen

DNA Repair<4strong>