Genes and MutationsSection 14.1

GenesGene: a segment of DNA

that codes for a specific protein

Human DNA contains about 24,000 genes

Gene regulation allows only certain genes to be “turned on” in certain cells

GenesProteins called

transcription factors attach to DNA and turn certain genes “off” or “on”

Much DNA, as far as scientists know, does not code for a specific gene

MutationsMutations are small

changes in a gene

Depending on the mutation, the resulting protein can be identical, slightly different, or very different

Causes of MutationsSome mistakes in

replication are not corrected

Chemicals can alter DNA

Radiation can alter DNA

Nuclear radiation Cell phones UV light

Mutations can be harmful!Some mutations may

cause a protein not to function

Other mutations may cause a trait that makes it difficult for an organism to survive

Mutations can be beneficial!Some mutations

may cause a trait that make it easier for an organism to survive or reproduce

These mutations are absolutely essential for evolution to occur

Examples of Genetic DisordersColor blindness

Cystic fibrosis

Down syndrome

Hemophilia

Sickle-cell anemia

Huntington’s disease

Genetic Basis of Mutations

Mutations as Changes in DNAPoint mutation

(a.k.a. substitution) – change of one DNA base

Insertion or deletion – addition or subtraction of one DNA base

A portion of a gene…T A C A T G G C G G A

C G A A

What mRNA strand would be created during transcription?

What polypeptide would be created during translation?

Mutations1. Change the 4th “G” base to an “A” base.

Silent mutation results in no change in the polypeptide

Possible because of redundancies (repetition) in the amino acid code

Mutations2. Change the 2nd “G” base to a “T” base.

Missense mutation changes a single amino acid in the polypeptide

Mutations3. Change the 1st G” base to a “C” base.

Nonsense mutation changes a single amino acid in the polypeptide to a “STOP” codon

Extremely dangerous mutation, as the entire polypeptide will not be created

Mutations4. Delete the 2nd “T” base.

Frameshift mutation results from an insertion or deletion and changes an amino acid and every subsequent amino acid in the polypeptide

Extremely dangerous mutation, as a large portion of the polypeptide may be altered