From DNA Mutations to Selectable Phenotypes
to Genetically Diverged Populations
Teaching Evolutionary Principles by Integrating Biology’s Sub-disciplines

Goals for today’s session
• Why were Mendel’s peas
wrinkled?
• Cell biology of natural
selection on a beach.
• People are evolving, too!
wcco.com
Jim Smith
Michigan State University
Lyman Briggs College
Department of Entomology
jimsmith@msu.edu
On the Origin of Species
Darwin’s Logic

Variation under Domestication


We can easily see how people have
artificially selected “favored races” of
pigeons, sheep, roses and dahlias.
Natural Selection

One can easily also envision how this
same “selection” process can occur
naturally, in the wild.
The patterns of variation we observe in
nature support this idea.
Downe House from the Sand Walk
We’ll Follow Similar Logic Today
Mendel’s Peas

Artificial Selection

Wrinkled Peas are sweeter, and therefore people
will tend to select them and propagate them.
Hopi’s Mice

goodlifefarm.com
Natural Selection


Mice with white coats on white sand beaches
are less visible to prey.
Thus, they are less subject to predation and
selectively survive.
Hoekstra et al. 2006. Science 313: 101–107.
Alleles at a locus
Basic Principles
of Mendelian
Genetics
R
Genotype
Phenotype
R
R = Dominant allele for seed shape (round)
r = Recessive allele for seed shape (wrinkled)
Mendelian
Genetics
= Round-seeded phenotype
= Wrinkled-seeded phenotype
Mother
Rr
Female gametes
Father
Rr
Male gametes
R
r
R
RR
Rr
Rr
rr
r
Resulting genotypes: 1/4 RR : 1/2 Rr : 1/4 rr
Resulting phenotypes:
3/4
: 1/4
Freeman 1e Fig. 10.7
Why are wrinkled peas wrinkled?
(use the word, “protein” in your answer!)
R
Freeman 1e Fig. 10.2
Hint: What does “R” do?
Integrating Across Sub-disciplines
The Central
Dogma of
Molecular
Biology

Connect to Mendelian
Genetics

Connect to Evolution
What does the “R” gene do?
How does the SBEI protein lead to round seeds?
Freeman 1e Fig. 10.2
It gives rise to highly branched starch (amylopectin)
R
Highly branched starch in the
seeds leads to seeds with low
water content. When the seeds
dry, they stay round.
Modified from Campbell 4e Fig. 5.6
Molecular Basis of
Wrinkled vs. Round Peas
R
protein
R allele  Functional SBE Protein
r protein
r allele  Non-Functional SBE
800 bp fragment of DNA inserted
Courtesy of Dr. April Cognato,
Mich. St. Univ., Dept. Zoology
What does the “R”
symbol represent?
3550 nucleotides!
R
What does the “R” gene do?
The “R” gene DNA encodes a starch
branching enzyme protein (SBEI)!
A polypeptide of approx. 960 amino acids
R
Gregor Mendel

Observed 5474 round seeds
(dominant) and 1850 wrinkled
seeds (recessive)
• 5474/1850 = 2.96:1

Do a c2-test
• Is this a 3:1?
Phenotypic Variation
Basic Principles
of Evolution


Connect to Mendelian
Genetics
Environment w/ Selection
Connect to Cell and
Molecular Biology
Evolved Population
Bridging Mendel and Darwin

Observed 5474 round seeds
(dominant) and 1850 wrinkled
seeds (recessive)
• 5474/1850 = 2.96:1

How would the wrinkled allele (r)
go to fixation in a population?
R
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A Population
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How do new species evolve?
From:http://evolution.berkeley.edu/e
volibrary/article/_0/history_20
Merging Genetics, Molecular Biology, and Evolution
Alleles at a locus
DNA
Phenotypic Variation
R
Genotype
Phenotype
Peas Connect Parallel Paths!!
RNA
Protein
Environment w/ Selection
Evolved Population
Beach Mice - The Mc1r locus and MC1R Protein
Hoekstra et al. 2006
Mice living on exposed white sand
beaches along the Gulf Coast have
different Mc1r allele frequencies
The mutant Mc1r gene has a single C  T
substitution, leading to the substitution of Cysteine
for Arginine at position 65 in the MC1R protein
MC1R proteins (polypeptides) with the R65C
amino acid substitution bind -MSH less well
and produce less cAMP
From: Barsh 1996 Trends in Genetics
R65C MC1R Proteins Function Differently in
Melanocytes than their Counterparts
Steiner et al. 2009. Mol Biol Evol 26: 35-45.
Clicker Q1. The ultimate reason for the
lighter coat colors of the mice on the white
sand Gulf Coast beaches was:
A. predation by hawks and other carnivores on beach mice that do not
carry the mutant allele.
B. a substitution of Cys for Arg at position 65 of the MC1R protein.
C. a substitution of T for C at position 193 of the Mc1r gene nucleotide
sequence.
D. the failure of melanocytes to lay down melanin pigment in the coat
hairs of the lighter colored beach mice.
E. the poorer binding affinity for -MSH and the lower amount of cAMP
produced by individuals with the R65C MC1R protein.
Clicker Q2. The C  T substitution at
position 193 of the Mc1r gene:
A. arose by a mutation in the beach mouse populations in
response to a need for protection from predation.
B. leads to the failure of melanocytes to make an MC1R protein.
C. arose by a mutation, which increased in frequency because it
was selectively advantageous in the beach mouse
populations.
D. had no effect on the beach mouse populations.
E. produced an alternate allele that was detrimental to mice on
the white sand beaches.
Humans Are Evolving,
Too!!
Organismal Biology Honors
Presentation
[2 Lyman Briggs students]
Jaw Muscle-Ape
Archaic Ape, Humanoidsheavy jaw (myofascial)
muscles
 Muscle attached to sagittal
crest on top of head
 Continued to modern apes

– Allows for hard chewing
– Important for raw vegetable
diet
Currie P. 2004. Nature 428: 373-374.
Stedman H, et al. 2004. Myosin gene mutation correlated with
anatomical changes in the human lineage. Nature 428: 415-418.

Jaw Muscle-Humans

Smaller jaw muscles then
apes
– Decrease in plant
consumption
– More reliance on hands

Currie P. 2004. Nature 428: 373-374.
Decrease in muscles
eliminated sagittal crest
How did this happen?

Myosin Heavy Chain (MYH)
– Critical proteins in sarcomere
– Myosin binds to actin and uses ATP to pull itself
 Give contractile force to skeletal muscle
– Different types for contraction in different muscles
– Loss of MYH gene cause large loss of muscle
MYH: Humans vs. Chimps

MYH 16 in both Human & Chimps
– Temporalis and Masseter Muscles

Human gene mutated
– Accumulate less MYH 16 protein
Seven non-human species compared to six
geographically dispersed human populations
Bibliography and Resources
Wrinkled Peas

Guilfoile P. 1997. Wrinkled Peas & White-Eyed Fruit Flies: The Molecular Basis of Two
Classical Genetic Traits. The American Biology Teacher 59: 92-95.

Bhattacharyya MK, et al. 1990. The wrinkled-seed character of pea described by Mendel is
caused by a transposon-like insertion in a gene encoding starch-branching enzyme. Cell 60:
115-122.
Beach Mice

Hoekstra HE, Hirschmann RJ, Bundey RA, Insel PA, Crossland JP. 2006. A single amino acid
mutation contributes to adaptive beach mouse color pattern. Science 313: 101–107.
Human Jaws

Stedman H, et al. 2004. Myosin gene mutation correlated with anatomical changes in the
human lineage. Nature 428: 415-418.
Slides from today’s session:
http://www.msu.edu/user/jimsmith/nabt_2010.pdf