Allele Frequency
What is an allele?
One or two alternative versions of a gene.
What is the difference between an allele and a trait? Give an example.
An allele is a version of a gene, while a trait is the observable characteristic influenced by that gene.
Example: The allele for blue eyes or brown eyes; the trait is eye color.
Peppered Moth
Allele A: Light-colored wings
Allele a: Dark-colored wings
Environment Change: Trees become covered in soot during the Industrial Revolution.
Question: Which allele gives camouflage and increases survival from predators?
Allele a: Dark-colored wings
In a population of beetles, some are green and some are brown. Birds can see green beetles easily on the brown dirt and eat them more often. Over time, the population has more brown beetles than green. Which mechanism of evolution is this?
Natural Selection
What is allele Frequency?
Proportion of a specific allele in a population. Measures how common an allele is.
A plant has the genotype Tt for height. Identify the alleles and the trait.
Alleles: T and t
Trait: Plant height
. Drought and Seed Size in Plants
Allele L: Produces plants with large seeds (can survive drought better, but fewer seeds overall).
Allele S: Produces plants with small seeds (many seeds, but less drought-resistant).
Environment: A multi-year drought occurs.
Question: Which allele increases the likelihood of seedlings surviving in dry conditions?
Allele L:
Produces plants with large seeds (can survive drought better, but fewer seeds overall).
A hurricane randomly wipes out most of a lizard population living on a small island. The surviving group happens to have mostly short tails, even though tail length doesn’t affect survival. In the next generation, short tails are common simply by chance.
Genetic Drift
What is the difference between a dominant and a recessive allele?
Dominant alleles are expressed over recessive alleles.
Is eye color an allele or a trait? Justify your answer.
Eye color is a trait.
The alleles are the gene versions (e.g., blue, brown, green) that determine which form of the trait is expressed.
Allele W: White fur
Allele B: Brown fur
Environment: Snowy winter landscape vs. forest floor in summer.
Question: Which allele gives camouflage and reduces predation risk in each environment?
Winter (snow): White allele (W) is advantageous (camouflage in snow).
Summer (forest floor): Brown allele (B) is advantageous (camouflage in dirt/grass).
A plant suddenly develops a new allele that produces purple flowers instead of red. This allele did not exist in the population before.
Mutation
How can natural selection affect allele frequency?
If natural selection favored a specific allele, the allele frequency would increase overtime.
If it is not a favored allele, the allele frequencies will decrease.
In humans, the gene for earlobe attachment has two alleles: free (E) and attached (e). What trait does this gene influence?
Trait: Earlobe attachment (whether earlobes are free or attached)
Temperature Tolerance in Fish
Allele C: Enzyme variant works best in cold water
Allele H: Enzyme variant works best in warm water
Environment: Lake temperature rises due to climate change.
Question: Which allele provides better metabolic efficiency in the new environment?
Cold water: Cold-adapted allele (C) is advantageous (enzyme works efficiently).
Warm water: Heat-adapted allele (H) is advantageous (better metabolism at higher temps).
On a small island, a few frogs are stepped on by accident by a herd of deer. The survivors, purely by chance, are all green instead of brown. Now most of the next generation is green.
Genetic Drift
Describe how allele frequencies can be used in evolutionary biology.
The change in allele frequencies can be used to indicate the evolution of a population.
Explain how different alleles of the same gene can produce different traits.
Different alleles code for variations of a protein, which can change the phenotype.
Example: One allele for pea flower color codes purple, another allele codes white, producing different traits.
A population of mice lives in a desert with two main habitats: light-colored sand dunes and patches of dark volcanic rock.
Allele L: Produces light-colored fur
Allele D: Produces dark-colored fur
Question: Which allele would be advantageous in the sand dune habitat? Which allele would be advantageous in the volcanic rock habitat?
Sand dunes: Light-colored fur (L) is advantageous (camouflage).
Volcanic rock: Dark-colored fur (D) is advantageous.
In a population of rabbits, some have thicker fur and some have thinner fur. A sudden cold winter arrives, and only the thick-fur rabbits survive and reproduce.
Natural Selection