045 Lesson Plan Genetic Diversities

Genetic Diversity & Phylogenetic Trees
Subject: Science
Grade Level: 8th – 12th Grade
Rationale or Purpose: The purpose of this lesson is for the students to learn about
genetic diversity. Students will:
• relate genetic diversity to population size and family size
• discover what causes genetic diversity and why it can be important
• apply what they know about genetic diversity to solve a problem of shrinking
population sizes in a pygmy rabbit in the Northwestern United States
Materials per group:

• Pictures of various plants and animals
• Computer with Internet access
• Worksheet for the Pygmy Rabbit Activity
Lesson Duration: 90 minutes (can be broken up into two 45 minute classes or one 90
minute class)
Source of Lesson: Hot Science – Cool Talks CD-ROM # 45: “The History and Future
of Whales”
TEKS Objectives:
Biology:
(6C) identify and illustrate how changes in DNA cause mutations and evaluate the significance
of these changes;
(7B) illustrate the results of natural selection in speciation, diversity, phylogeny, adaptation,
behavior, and extinction.
(12D) Identify and illustrate that long-term survival of species is dependent on a resource base
that may be limited
Aquatic Science:
(8B) analyze the cumulative impact of natural and human influence on an aquatic system;
(8D) analyze and discuss human influences on an aquatic environment including fishing,
transportation, and recreation.
ENGAGE: As the students come into class, have pictures of various animals and plants
on the overhead. Ask the students to write if they think these things are related to modern
day humans (yes or no answers are fine). Then tell them to rank the animals that they
think are related to humans in order from which species they think are the closest to
humans to which ones are the furthest from humans (less related). Some examples of
pictures are Sponges, Monkeys, Birds, Bacteria, Insects, Fungi, a tree, etc. The Tree of
Life Web Project (www.tolweb.org/tree/) is a good website to look for pictures.
Teaching Module developed by Katie Stong

Environmental Science Institute (www.esi.utexas.edu)
After students complete this, explain that genetic diversity is the measurement of how
closely related two species are and it is measured as a percentage of shared DNA. The
closer relatives will have more DNA in common because they would have had less time
to evolve separately. Show them the phylogeny of whales (see Figure 1), and explain that
the longer the arm is in the phylogenies, the more genetic difference there is between a
species and it’s closest ancestor.
Figure 1. Phylogenetic Tree of Whales.
EXPLORE: Show the students two phylogenies: one of whales (Figure 1) and one of
humans (Figure 2). Ask students which phylogeny shows more genetic diversity. Note:
Figure 1 and 2 are not drawn to the same scale, so branch length should not be compared
to estimate genetic diversity.

Homo ergaster
Homo habilis
Australopithecus
Homo neanderthalensis
Homo erectus
Homo sapiens
Figure 2. Human Phylogenetic Tree.
Questions to ask the Students:

• How many species of humans (Homo sapiens) are there? 1
• What is the current human population? Over 6 billion
• How many species of Whales (Cetacean) are there? About 79
• What is the current Cetacean population? Under 6 billion
• Does larger genetic diversity necessarily mean larger population size? No, only 1
species of Homo sapiens and many more individuals in the population
• Is it better to have a larger or smaller genetic diversity with in the population? It is
better to have a large genetic diversity. For more information refer to the Danger
of Low Populations learning module
EXPLAIN: Discuss the questions above with the students. Then discuss with the
students mutations as the source of genetic diversity. Explain how some mutations are
good, many are neutral, and others are deleterious (bad). Explain how environmental
factors can affect genetic diversity (for example: niche specialization in beetles).
Which genes do scientists use (ones that do not code for proteins) to determine genetic
diversity across species (there are more notes about mutations at the end of this
document).
ELABORATE: Revisit the question of how we would remedy the problems of

shrinking populations that inevitably lead to the lowering of genetic diversity. Allow the
students to use the computers and read the prompt about decreasing genetic diversity in
Pygmy rabbits in Washington State (paragraphs 1-5). After the students read, give them
10 minutes to fill out the three questions (listed below in the evaluation section) while
they think of their solution and discuss what they could do to increase the genetic
diversity in the pygmy rabbit population. Then give the students the opportunity to share
their ideas with the class.

• Breeding Projects with the pygmy rabbit website:
http://wdfw.wa.gov/wlm/diversty/soc/pygmy_rabbit/index.htm
• This activity allows you as a teacher to relate the lesson to what is happening in
the real world and you could also relate it to the job of a biologist to allow your
students to see what jobs a biology background is useful for.
• Teachers may also want to think about printing out the first five paragraphs from
the Pygmy Rabbit site so the students don’t read what the scientists have already
done.
EVALUATE: Have the students turn in the sheet of paper with the questions on it from
the Pygmy Rabbit Breeding Project Activity.
Questions for the Pygmy Rabbit Breeding Project Activity:

1. What has caused a decrease in genetic diversity in the Pygmy rabbits?
2. How many populations of pygmy rabbits are left in the wild?
3. Pretend that you were a scientist in Washington working on the Pygmy Rabbit
problem. Brainstorm 2-3 ways that you could increase the genetic diversity in the
population.
MUTATION NOTES: DNA is read by ribosomes in sets of 3 base pairs called a

nucleotide sequence or a codon. Every codon codes for an amino acid, which are the
building blocks of proteins. There are only 23 amino acids and 65 codons, so some
codons code for more than one amino acid. The outcome of the redundancy is that if a
mutation happens on the third base pair of a codon it is usually silent, meaning that the
amino acid it codes for will not change and so it has no effect. If a mutation happens on
the 1st or 2nd base pair of a codon it is called a point mutation and it is more serious
because it can result in the change of the amino acid that was coded for that region. The
last type of mutation is a deletion or an insertion, meaning that while DNA is replicating
the DNA polymerase, the enzyme responsible for replication, adds or deletes a base pair
entirely which results in a frame shift, which means that all of the amino acids after the
mutation are affected. This is the worse type of mutation. Most mutations are deleterious
or moderately deleterious, and mutations are rarely beneficial. However, in novel
situations or rapidly changing environments mutations can be highly advantageous. This
is because they create diversity and in situations where the environment is not stable, the
more diversity that is present, the more likely one individual will be able to survive and
procreate in the new environment.


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Genetic Diversity & Phylogenetic Trees

Grade Level: 8th – 12th Grade

Materials per group:

Teaching Module developed by Katie Stong

Figure 1. Phylogenetic Tree of Whales.

Teaching Module developed by Katie Stong

Figure 2. Human Phylogenetic Tree.

Questions to ask the Students:

ELABORATE: Revisit the question of how we would remedy the problems of

Teaching Module developed by Katie Stong

Questions for the Pygmy Rabbit Breeding Project Activity:

MUTATION NOTES: DNA is read by ribosomes in sets of 3 base pairs called a

Teaching Module developed by Katie Stong

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