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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 SyndromeEdwards Syndrome
Trisomy 21~Down Syndrome
Trisomy 18~ Edwards Syndrome
-One single change in a DNA nucleotide is made therefore only affecting one single gene.
2. Gene mutation:
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.
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