MUTATIONS BIOLOGY HONORS WHAT IS A MUTATION A

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.