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Mutations
What are mutations?
-They are mistakes made in
our genetic code, which may
or maynot result in the wrong
protein being made.
Mutagens:
Are any chemical or radiation that
causes a change in our genetic code.
Examples:
X-rays, UV sunrays, asbestos and
coal dust.
Carcinogens:
-Are mutagens that cause a mistake in the
genetic code that leads to uncontrollable cell
division.
- This results in CANCER.
-Examples include: Mercury, UV rays and
cigarettes
Two categories of mutations:
Germ mutation:
-mutations which occur in the sperm or the
egg. If fertilized this mistake would be
passed on to the child.
Example: Sickle cell anemia
Somatic mutations:
-mutations which occur in a body cell.
These cells are not passed on to the
offspring.
-Example: Skin cancer
Types of mutations (either germ or
somatic):
1. Chromosomal mutations:
-entire chromosomes is affected
therefore many genes are involved resulting
in the most severe forms of mutations.
-Example: Down Syndrome
Edwards Syndrome
Trisomy 21~Down Syndrome
Trisomy 18~ Edwards Syndrome
2. Gene mutation:
-One single change in a DNA
nucleotide is made therefore only
affecting one single gene.
Example:
Albinism:
Types of gene mutations:
1. Silent or Neutral Mutation
-a change in one base does
not alter the amino acid sequence.
2. Missense Mutation:
-one DNA nucleotide is changed
causing it to code for a different
amino acid. This mistake still codes
for an amino acid BUT just the wrong
amino acid.
3. Nonsense Mutations:
-one DNA nucleotide is changed
forming a stop codon in the middle of a
gene resulting in a shortened amino acid
sequence that codes for NO protein.
4. Frameshift mutation:
-one or two nucleotides gets
added to a gene resulting in the
entire sequence to get shifted down
and throwing off the entire amino
acid sequence.