CH. 12 NOTES PART 4: CAUSES OF
MUTATIONS AND GENE
REGULATION
THURSDAY FEB. 18, 2016
PUT YOUR NAME ON YOUR NOTES!
REVIEW
• A gene mutation is a permanent alteration in the DNA
sequence that makes up a gene, such that the sequence
differs from what is found in most people.
• Mutations range in size; they can affect anywhere from a
single dna building block (base pair) to a large segment of a
chromosome that includes multiple genes.
CAUSES OF MUTATIONS
1. DNA fails to copy accurately: DNA replication is highly
accurate due to proof-reading and editing ability of
numerous enzymes, including DNA polymerase.
 As a result, it is estimated that only 1 in every 1,000,000,000
(billion) bases is incorrect when DNA is copied. This is rare but
it does happen.
CAUSES OF MUTATIONS
2. Hereditary mutations are inherited from a parent and are present
throughout a person’s life in virtually every cell in the body.
• These mutations are also called germline mutations because they are
present in the parent’s egg or sperm cells, which are also called germ
cells.
• When an egg and a sperm cell unite, the resulting fertilized egg cell
(the zygote) receives DNA from both parents.
• If this DNA has a mutation, the child that grows from the fertilized egg
will have the mutation in each of his or her cells.
CAUSES OF MUTATIONS
3. Acquired (or somatic) mutations occur at some time during a
person’s life and are present only in certain cells, not in every cell in
the body. These changes can be caused by environmental factors:
A. Harmful chemicals: pay attention to warning labels
regarding strong chemicals, especially around children! Chemicals
emitted from rubber factories, industrial solvents, and run-off from
plastic manufacturing plants can cause mutations to DNA that can
result in cancer.
CAUSES OF MUTATIONS
B. Sunlight & UV radiation: our bodies need sunlight for making
proteins such vitamin D which is synthesized on exposure to
sunlight.
• However, harmful UV radiation from the sun can do some serious
damage.
• Exposure to strong sunlight or UV tanning bulbs tends to damage
cellular systems as well as DNA.
CAUSES OF MUTATIONS
C. Hydrocarbons: hydrocarbons are chemicals present in
tobacco smoke, vehicle exhausts, products of burning of
fossil fuels and charred/overcooked meat.
• Meat products should be cooked properly so that any
bacterial or parasitic life forms can be destroyed.
• However, the buildup of carbon products in burnt meat can
be harmful to DNA.
WHY DO MUTATIONS MATTER?
• To function correctly, each cell depends on thousands of proteins to do their
jobs in the right places at the right times.
• Sometimes, gene mutations prevent one or more of these proteins from working
properly.
• By changing a gene’s instructions for making a protein, a mutation can cause
the protein to malfunction or to be missing entirely. When a mutation alters a
protein that plays a critical role in the body, it can disrupt normal development
or cause a medical condition.
• A condition caused by mutations in one or more genes is called a genetic
disorder.
WHY DO MUTATIONS MATTER?
• In some cases, gene mutations are so severe that they prevent
an embryo from surviving until birth.
• These changes occur in genes that are essential for
development, and often disrupt the development of an
embryo in its earliest stages.
• Because these mutations have very serious effects, they are
incompatible with life.
WHY DO MUTATIONS MATTER?
• It is important to note that genes themselves do not cause
disease—genetic disorders are caused by mutations that
make a gene function improperly.
• For example, when people say that someone has “the cystic
fibrosis gene,” they are usually referring to a mutated version
of the gene, which causes the disease. All people, including
those without cystic fibrosis, have a version of the gene.