Biology
Class Notes
Lesson 24 Mutations and Genetic Variation
Objective: 3.1.3
*DNA codes for amino acids, which comprise proteins, via mRNA.
*Each protein is made of a few to several amino acids, and if only one is
changed, an altered protein may form.
Mutation: A change in the normal DNA sequence resulting from random
error or the effect of a mutagen.
Mutagen: Any agent that changes the DNA of an organism.
Ex: X-Rays, Ultraviolet Radiation, Ionizing Radiation, certain chemicals,
and viruses.
Ex: Ethidium bromide (EtBr): An agent commonly used as a fluorescent
tag in agarose gel electrophoresis because it will fluoresce when
exposed to ultraviolet light.
Types of Mutations
1. Base Pair Substitution: A mutation in which one nucleotide base
replaces another.
2. Base Insertion: The addition of one or more bases into a nucleotide
sequence.
3. Base Deletion: The removal of one or more bases from a nucleotide
sequence.
4. Nondisjunction: A chromosomal mutation that produces an offspring
with an incorrect number (more or less) of chromosomes.
Ex: Nondisjunction of sex chromosome causes Kleinfelter
Syndrome (XXY).
Ex: Turner Syndrome (X_, or XO)
Ex: Down Syndrome (three copies of chromosome 21).
Effects of Mutations
*Recall that cells can be categorized as somatic cells or gametes. Somatic
cell mutations are not inherited, but germ/gamete mutations are
inherited via the sex chromosomes.
Somatic Mutations
 Usually result in cancerous or uncontrolled growth of cells.
 Can be caused by chemical or viral mutagens.
Ex: Chemicals in asbestos and tobacco can cause uncontrolled cell
growth in lungs.
Ex: Human Papillomavirus (HPV) causes cervical cancer by
attaching to the DNA of cells in the cervix. The cells eventually
rupture causing copies of the virus to be release to infect other
cells.
Germ Mutation:
 Can be passed from parent to offspring.
 Can effect survival of the offspring and change the traits of
descendants.
Ex: Hemophilia: A disorder that slows blood clotting.
Ex: Color blindness: A disorder that hinders the ability to
distinguish different colors.
Key Words:
Mutation
Mutagen
Base-pair substitution
Base insertion
Base deletion
Nondisjunction
Autosome
Somatic mutation
Germ mutation