how mutation affect genes and what causes mutations

1. MUTATIONS CAN CHANGE
THE MEANING OF GENES
(last subtitle of chapter 11 -THE LANGUAGE OF LIFE)

2. DNA and the Language of Life (chapter 11 of the book)
•MUTATIONS CAN CHANGE THE
MEANING OF GENES
2

3. HOW MUTATIONS AFFECT GENES
Two general categories:
•Base substitutions
•Base insertions or deletions

4. HOW MUTATIONS AFFECT GENES
Occasionally, a base substitution causes no
change to a protein, but sometimes it results in a
change that affects the function of a protein,
sometimes drastically (as in the base substitution
leading to sickle cell disease).
Base substitutions
Is the replacement of one base or nucleotide with another

5. HOW MUTATIONS AFFECT GENES
Base substitutions
Some base substitutions show no effect on the protein that is
made:
In the genetic code, several amino acids have more than one
codon.
Both GAA and GAG code for the same amino acid (Glu).
If a mutation to DNA causes the mRNA codon to change from GAA
to GAG, no change in the protein product would result.
This is a "silent mutation."

6. HOW MUTATIONS AFFECT GENES
• MUTATIONS CAN CHANGETHE MEANING OF GENES

7. HOW MUTATIONS AFFECT GENES
Base insertions or deletions
Because mRNA is read as a series of triplets, adding or
subtracting nucleotides may alter the triplet groupings of
the genetic message.
Therefore, all the nucleotides that are "downstream" of the
mutation will be regrouped into different codons.
These new codons code for new amino acids.The result will
be a different, and probably nonworking, protein.
nsertion or deletion of one or more nucleotides in a gene is usually more
isastrous than the effects of a base substitution.

8. HOW MUTATIONS AFFECT GENES
• MUTATIONS CAN CHANGETHE MEANING OF GENES

9. WHAT CAUSES MUTATIONS?
• Mutations may occur when errors are made during DNA replication, or
when errors are made during chromosome crossovers in meiosis.
Physical or chemical agents that cause mutations
• Physical mutagen: high-energy radiation (such as X-rays and
ultraviolet light)
• Chemical mutagen:chemicals that are similar to normal DNA
bases but cause incorrect base-pairing when incorporated into
DNA
MUTAGENS:

10. WHAT CAUSES MUTATIONS?
• Although mutations are often harmful, they can alter a protein in a
way that may be beneficial in certain environments
Example: a genetic mutation is responsible for the dark
color seen in some females of the tiger swallowtail
butterfly species, Papilio glaucus.
The mutation may be advantageous when the
environment includes a related species, the poisonous
black swallowtail Battus philenor.
Predators that avoid eating the black swallowtail may
also avoid eating its mimic, the dark form of P. glaucus.

11. WHAT CAUSES MUTATIONS?
•If a mutation is present in an organism's gametes,
it can be passed on to its offspring. Mutations are
the ultimate source of genetic diversity in the
living world

12. CONCEPT CHECK
Why base subtitution is often less harmful tan a base
deletion or insertion?
•A base subtitution potentially affects only one amino
acid of the polypetide, but a base deletion or insertion
affects all the amino acids “downstream” from where it
occurs.

13. CONCEPT CHECK
How mutation could be helpful rather tan
harmful?
•If it alters a protein in a way that benefits
an organism in its environment

14. CONCEPT CHECK
Examples of mutagens
•X-rays, UV light, some
chemicals