Unit 3: Evolution
Lesson 1: Mutations & Artificial Selection
What is evolution and why is it important?
Genetic Diversity and Evolution
 The mechanism that drives evolution is natural selection.
 Natural Selection: the way in which nature favours the reproductive success of some
individuals within a population over others.
 Genetic diversity must be present for nature to favour some individuals over other
Mutations and Genetic Diversity
 Mutations are the source of genetic variation
How Mutations Occur
Substitution
A substitution is a mutation that exchanges one base for another (i.e., a change in a single
"chemical letter" such as switching an A to a G).
-Such a substitution could cause a small change in the protein produced.
For example,sickle cell anemia is caused by a substitution in the beta-hemoglobin gene,
which alters a single amino acid in the protein produced.
Insertion
Insertions are mutations in which extra base pairs are inserted into a new place in the
DNA.
Deletion
Deletions are mutations in which a section of DNA is lost, or deleted.
Types of Mutations
Neutral mutation - a mutation that does not result in any selective advantage
or disadvantage.
Harmful mutation - any mutation that reduces the reproductive success of
an individual and is therefore selected against; harmful mutations do not accumulate over
time
Beneficial mutations - are favoured by natural selection and accumulate over time
Artificial selection - directed breeding in which individuals that exhibit a particular trait are
chosen as parents of the next generation; artificial selection is used to produce new breeds or
varieties of plants and animals
Guide to Artificial Selection
1. Choose a useful species that can be bred in captivity.
2. Breed a large number of individuals.
3. Choose a trait that you wish to favour, such as large size, a particular colour, or sweetness.
4. Identify individuals that exhibit the favoured trait most strongly.
5. Breed only these individuals to produce the next generation of individuals.
6. Repeat Steps 4 and 5 over many generations.
Limitations of artificial selection
 Artificial Selection is limited by the genes that are present in the current population.
Homework Questions
1. The chances of any one individual being born with a beneficial mutation is very low. How then is it
possible for mutations to play such a key role in evolution?
2. How might it be possible for a neutral mutation to play an important role in the evolution of a species?
3. Explain why harmful mutations do not accumulate over time and cause harm to populations.
4. Use the evolution of antibiotic resistance to show how a mutation that is advantageous for one species
can be harmful for another.
K/U
5. Most wolves look quite similar. Use the domestication of dogs to illustrate the genetic diversity that is
contained within the wolf population.
K/U
6. All domestications of plants and animals begin with humans selecting a wild species living nearby. Use
the Internet and other sources to research where each of the following domesticated species originated:
(a) chicken
(b) pig
(c) cattle
(d) corn
(e) wheat
(f) rice
(g) chocolate
(h) coffee
(i) squash
K/U
7. Using a specific example, outline a hypothesis and simple step-by-step procedure a breeder could use
to create a breed with a desired trait.
TI
8. How have modern genetic engineering methods changed the way that plant breeders develop plants with
new and potentially valuable traits?
9. How do the genetic diversity of a population and mutation rates limit the ability of breeders to create
organisms with desired traits?
K/U
10. In 1975, Japanese scientists discovered bacteria feeding on nylon in a chemical waste water pond.
Nylon is a synthetic compound that was invented in 1935. Do online research to find out how mutations are
thought to have produced this “nylon bug.” Also learn how scientists have induced other
bacteria to evolve the ability to feed on nylon.
11. The discovery of the mutation responsible for the short legs of certain dog breeds was made by
scientists at the National Human Genome Research Institute. Use the Internet and other sources to find
out the following:
(a) Why were human geneticists interested in this dog trait?
(b) How did the scientists conduct their study? How many dogs did they investigate?
(c) What type of genetic change was responsible for this form of dwarfism?
1. Although the chances of any one individual being born with a beneficial mutation is very low, the
very large numbers of individuals in most populations and the great number of reproductive
events spanning millions of years and thousands of generations mean that mutations are actually
extremely common. They therefore generate a great deal of genetic variation and therefore play a
key role in evolution.
2. A neutral mutation may have no effect at the time is made, but result in a beneficial trait at a later
time because of a changing environment or by making another mutation possible. For example,
the duplication of an important gene is a neutral mutation at the time, but the copy of the gene
may mutate. The neutral mutation therefore plays an important role in the evolution of the species.
3. Harmful mutations are selected against. They reduce the reproductive success of the individuals
that possess them and are therefore self limiting.
4. Mutations that increase antibiotic resistance benefit the bacteria that possess them but cause
potential harm to humans who might be infected with the bacteria.
5. Artificial selection was used to select for particular traits that wolves possessed. This enabled
breeders to develop dogs with an enormous diversity of shapes, sizes, and behavioural traits. The
diversity displayed by dogs therefore reflects the genetic diversity that is contained in the wolf
population.
6. (a) chicken: Asia
(b) pig: Asia
(c) cattle: Asia
(d) corn: Mesoamerica
(e) wheat: Middle East
(f) rice: Asia
(g) chocolate: South America
(h) coffee: Africa
(i) squash: North America/Central America
T/I
7. Answers may vary. Sample answer: Hypothesis: A strawberry breeder could select the sweetest
strawberries as breeding stock generation after generation. The berries should become
increasingly sweet. First, the breeder should plant a large number of plants and sample their
berries. Then the breeder should choose the few plants with the sweetest berries and cross them.
Next, the breeder should sample the berries of all of the offspring and choose a few plants with
the sweetest berries and cross them. These steps would be repeated many times.
8. Modern genetic engineering methods insert genes into plants that code for specific traits found in
other species. Breeders no longer have to wait for new and valuable traits to appear after many
generations.
9. The genetic diversity and mutation rates of a population limit the ability of breeders because they
can only select traits from the traits possessed by the organisms. New traits (increased genetic
diversity) created by mutations are unpredictable and can be slow to develop.
10. Scientists believe a gene duplication event was responsible for at least one of the new enzymes
involved in nylon digestion. Scientists have caused other bacteria to evolve the same ability to
digest nylon by having them live in an environment with no other source of nutrients. They have
also used a plasmid to transfer the genes responsible into a strain of E. coli bacteria.
11. (a) Researchers were interested in the genetic causes of human dwarfism and decided to examine
the genetics of short-legged dog breeds.
(b) The scientists examined the genetic make-up (40 000 “markers”) of 835 dogs, including 95
with short legs.
(c) The scientists found that most short-legged dogs share a single genetic mutation: an insertion
of an extra, modified copy of a gene that codes for a growth-promoting protein. Scientists
hypothesize that the overproduction of the growth factor may cause errors in the timing or turning
on of growth receptors during development.