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Transcript
10-6 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 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 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 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 10-7 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 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 10-7 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… Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 10-7 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 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 10-7 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 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 10-7 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 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 10-7 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 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.
