1. 21.7 Genetic Mutations
A peacock with albinism does not produce the melanin needed to make bright colors for its feathers.
Learning Goal Identify the type of change in DNA for a point mutation, a deletion mutation, and an insertion mutation.

2. Genetic Mutation A mutation
is a change in the nucleotide sequence of DNA.
may result in changes to the sequence amino acids that affect the structure and function of cells.
results from mutagens, such as radiation and chemicals (possibly some viruses).
When a mutation severely alters proteins or enzymes, the new cells may not survive or the person may exhibit a disease or condition that is a result of a genetic defect.

3. Normal DNA Sequence
The normal DNA sequence produces an mRNA that provides instructions for the correct series of amino acids in a protein.

4. Types of Mutations
A point mutation is the replacement of one base in the template strand of DNA with another; this may cause a different amino acid to be inserted into the polypeptide.
A silent mutation occurs when a point mutation does not change the amino acid.

5. Mutations, Deletion and Insertion
In a deletion mutation, a base is deleted from the normal order of bases in the template strand of DNA. All the codons that follow are changed, producing a different sequence of amino acids from that point.
In an insertion mutation, a base is inserted into the normal order of bases in the template strand of DNA. All the codons that follow are changed, producing a different sequence of amino acids from that point.

6. Mutations, Deletion and Insertion
Deletion and insertion mutations change all the codons that follow.

7. Effects of Mutations
Some mutations do not cause significant changes in the primary structure of a protein.
For drastic changes in the amino acid sequence,
the structure of the resulting protein may lose its biological activity.
proteins (enzymes) may no longer catalyze reactions and substances may accumulate in the cells until they are poisonous.

8. Genetic Diseases
Genetic diseases result from a defective enzyme caused by mutation in its genetic code.
If the enzyme that converts tyrosine to melanin is defective, no melanin is produced, resulting in the genetic disease known as albinism.
Tyrosine is needed for the formation of melanin (skin and hair pigment).

9. Genetic Diseases

10. Study Check
Identify each type of mutation as a point mutation (P), an insertion mutation (I), or a deletion mutation (D). A. Cytosine (C) enters the DNA sequence. B. One adenosine is removed from the DNA sequence. C. A base sequence of TGA in DNA changes to TAA.

11. Solution
Identify each type of mutation as a point mutation (P), an insertion mutation (I), or a deletion mutation (D). A. Cytosine (C) enters the DNA sequence. (I) B. One adenosine is removed from the DNA sequence. (D) C. A base sequence of TGA in DNA changes to TAA. (P)