MUTATIONS
BIOLOGY HONORS
WHAT IS A MUTATION?
• A change in DNA
• Can cause changes
in organism
• Happen randomly
• Can be beneficial,
neutral, or harmful
For example, the golden color on
half of this Red Delicious apple was
caused by a mutation in its body
cells. Its seeds (reproductive cells)
will not carry the mutation.
MUTATIONS IN NONREPRODUCTIVE CELLS
• Causes:
• DNA fails to copy
correctly
• External influences
• Environment
• Examples: radiation, UV
light, chemicals
• Effects:
• Neutral
• Protein is not changed
• More than one codon
for an amino acid
• Harmful:
• Cancer
MUTATIONS TO REPRODUCTIVE CELLS
• Can have multiple effects
• Offspring is normal (mutation is silent)
• the mutation occurs in an intron
• the mutation occurs in an exon, but ends
up not affecting the amino acid
sequence of the protein.
• Small change occurs in offspring
• A single mutation caused this cat’s ears to
curl backwards slightly
• Big change occurs in offspring
• Some really important changes, like DDT
resistance in insects are sometimes
caused by single mutations.
• Mutations that cause the death of an
organism are called lethals—and it
doesn't get more negative than that.
• Example: Huntington’s disease
4 TYPES OF MUTATIONS
1.
Substitution
•
•
•
Exchange one base for another
Example: A to C
Example: Sickle-cell Anemia
Normally, red blood cells (RBCs) are rounded and
flattish, like a saucer. They pass easily through the
tiniest blood vessels. Red blood cells sickle or take on
the crescent shape when they carry an abnormal
form of hemoglobin called hemoglobin S. The
abnormality in hemoglobin S occurs because of the
presence of a faulty gene.
2.
Insertion
•
extra base pairs are inserted into a new place
in the DNA.
3.
Deletion
•
mutations in which a section of DNA is lost, or
deleted.
4.
•
•
•
Frameshift
Because codons three bases long,
substitutions, insertions and deletions
can alter a gene so that its message is
no longer correctly stated.
Consider the sentence, “The fat cat
sat.” Each word represents a codon. If
we delete the first letter the three letter
words (codons) that result don’t make
sense.
In frameshifts, a similar error occurs at
the DNA level, causing the codons to
be read incorrectly. This usually
generates proteins that are as useless
as “hef atc ats at” is uninformative.