1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Gene Control Prokaryotes turn genes on and off by controlling transcription Promoter DNA segment that allows a gene to be transcribed Helps RNA polymerase find where the gene starts Operator DNA segment that turns genes on or off Operon Region of DNA including the promoter, the operator, and genes that code for proteins Example : lac operon breaks down lactose sugar 10-6

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Gene Control Eukaryotes regulate genes at many points Exons Nucleotide segments that code for parts of the protein Introns Nucleotide segments that occur between exons Removed before mRNA leaves the nucleus Role is not clear

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mutations Change to the DNA code 2 types 1.Gene Mutation affect a single gene Occur during replication 2 types 1.Point Mutation One nucleotide is substituted by another Usually caught by DNA polymerase If not caught, it changes the DNA code 10-7

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mutations 1.Gene Mutation 2 types 2.Frameshift Mutation Insertion or deletion of a nucleotide Shift the entire DNA sequence because mRNA is read three nucleotides at a time Example : ABC DEF GHI JKL… With deletion: ABD EFG HIJ KL… 10-7

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mutations 2 types Chromosomal Mutation Affect an entire chromosome Occurs during meiosis 2 types 1.Gene duplication Homologous chromosomes did not align properly Crossing over does not result is equal sizes being exchanged Extra copies of genes on one chromosome and missing copies of genes on the other 10-7

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mutations 2 types Chromosomal Mutation 2 types 2.Translocation Piece of chromosome moves to non-homologous chromosome Like crossing over but with chromosomes that are not identical 10-7

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Results of Mutations Some cause death or diseases or malfunctions Some are not noticed at all Some lead to abnormalities that assist the organism and make them better suited for their environment 10-7

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Causes of Mutations Errors during replication These are usually fixed by DNA polymerase Mutagens Agents in the environment that change DNA Ex: UV rays and chemicals 10-7