Chapter 11.6Chapter 11.6

MutationsMutations

Definition-Definition- Mutation- a change in the DNA nucleotide sequence Mutation- a change in the DNA nucleotide sequence

Types of mutations:Types of mutations: Base substitution –replaces one DNA nucleotide base with Base substitution –replaces one DNA nucleotide base with

another one.another one. Base insertion- a DNA nucleotide base is added.Base insertion- a DNA nucleotide base is added. Base deletion- a DNA nucleotide base is deleted or removed.Base deletion- a DNA nucleotide base is deleted or removed.

Each mutation can cause Each mutation can cause a different protein to be made.a different protein to be made. Base substitutions are the least harmful.Base substitutions are the least harmful.

Why?Why? Some substitutions cause no change to the resulting protein; Some substitutions cause no change to the resulting protein; 64 codons=more than 1 codon can code for the same amino 64 codons=more than 1 codon can code for the same amino

acidacid Leucine= CUU, CUC, CUA, CUG,UUA, UUGLeucine= CUU, CUC, CUA, CUG,UUA, UUG

Insertion and Deletion mutations are more severeInsertion and Deletion mutations are more severe Affects all the nucleotidesAffects all the nucleotides downstream from the insertion downstream from the insertion

or deletion.or deletion. Resulting in many different codons and many new amino acids.Resulting in many different codons and many new amino acids. Affects the protein being made- protein may not function Affects the protein being made- protein may not function

properly.properly.

What causes a mutation?What causes a mutation? Random errors during DNA replication.Random errors during DNA replication. Physical and chemical agents- Physical and chemical agents-

mutagens.mutagens.high energy radiation- x-rays and high energy radiation- x-rays and

ultraviolet light ( shorter wavelengths).ultraviolet light ( shorter wavelengths).Chemicals that are similar to DNA Chemicals that are similar to DNA

bases and cause incorrect base-pairing bases and cause incorrect base-pairing when incorporated into the DNA.when incorporated into the DNA.

Not all mutations are harmful.Not all mutations are harmful. Mutations in DNA can be passed on to Mutations in DNA can be passed on to

offspring.offspring. Mutations are the source of genetic Mutations are the source of genetic

diversity in the living world.diversity in the living world.

Gene RegulationGene Regulation

All the cells in a multicellular organism carry All the cells in a multicellular organism carry the complete genetic code in their nucleus.the complete genetic code in their nucleus.

Cell specialization requires genetic Cell specialization requires genetic specialization.specialization.

Only a tiny fraction of the available genes Only a tiny fraction of the available genes needs to be expressed in cells of different needs to be expressed in cells of different tissues throughout the body.tissues throughout the body.