Natural Selection: Pocket Mice & the MC1R Gene

Simulation

Environment

Owl Predation

Number of Hunting Owls

2 owls

Owls hunt mice that contrast with the background.

Initial Population

Starting R Allele Frequency

Adjust before resetting simulation.

MC1R Gene

Molecular basis of coat color variation.

Generation

Next Gen

10s

Population

100

Allele Frequencies

R (dom) 5%

r (rec) 95%

Genotypes

RR 0

Rr 10

rr 90

Phenotypes

Dark 10

Light 90

Selection

Captured 0

Env Sandy

Pocket Mice Natural Selection

Explore how environmental change drives evolution through the MC1R gene

What You'll Observe

Gene Pool Visualization: Watch allele frequencies change in real-time as natural selection acts on the population.
Volcanic Eruption: Trigger an environmental change that shifts lava rock over the sandy desert, changing which mice are camouflaged.
Owl Predation: Owls hunt mice that stand out against the background - adjust their numbers to change selection pressure.
Generations: Every 10 seconds, surviving mice reproduce and pass on their alleles to the next generation.

The MC1R Gene

The MC1R gene controls coat color in pocket mice. The dominant R allele produces dark pigment (eumelanin), while mice with two copies of the recessive r allele (rr) have light, sandy-colored fur. Four amino acid differences between these alleles affect receptor function and pigment production.

Hardy-Weinberg Equilibrium

The Hardy-Weinberg principle states that allele and genotype frequencies remain constant across generations in the absence of evolutionary forces. This simulation uses Hardy-Weinberg equations to calculate offspring genotypes. Set owls to 0 to remove selection pressure and observe Hardy-Weinberg equilibrium in action.

p + q = 1

p = R freq, q = r freq

p² + 2pq + q² = 1

p² = RR, 2pq = Rr, q² = rr

Genetic Drift

Genetic drift is the random change in allele frequencies due to chance events, with stronger effects in small populations. Natural selection (owl predation) provides directional pressure, while genetic drift adds random variation.

1. Receptor Type

MC1R is a G protein-coupled receptor (GPCR) with 7 transmembrane domains that spans the melanocyte cell membrane.

2. Cell Location

MC1R is highly expressed on melanocyte cell membranes - the specialized cells responsible for producing pigment in skin and fur.

3. Activating Ligand

α-melanocyte-stimulating hormone (α-MSH) binds to the extracellular domain of MC1R, triggering receptor activation.

4. Downstream Effect

Receptor activation elevates cAMP levels via adenylyl cyclase, which increases eumelanin (dark pigment) production in melanocytes.

4 Key Amino Acid Differences

These mutations in the r allele reduce MC1R signaling, resulting in decreased eumelanin and lighter fur.

	R Allele (Wild-type)			r Allele (Mutant)
Position	DNA	mRNA	Amino Acid	DNA	mRNA	Amino Acid
18	CGC	GCG	Ala	TGC	ACG	Thr
109	CGG	GCC	Ala	TGG	ACC	Thr
160	CAG	GUC	Val	CGG	GCC	Ala
233	CGT	GCA	Ala	TGT	ACA	Thr