Biology · Simulation and virtual lab Free
Natural selection: beetle colour, camouflage and birds
Let birds hunt beetles on dark or light soil, breed the survivors and watch the population change colour.
- You will learn to
- Explain natural selection in terms of variation, selection pressure, survival and reproduction.
- Track changes in phenotype and allele frequency over generations.
- Explain why a recessive allele persists in a population.
- You will measure
- Numbers of dark and light beetles and the frequency of allele D in each generation.
- Time needed
- About 25–35 min
- Equipment
- Nothing extra. Real version: coloured paper dots or beans on light and dark cloth, a stopwatch and “predator” learners.
- Price
- Free: no payment, no account.
Virtual lab
Follow the steps with the simulation above (go back to the simulation ↑). Each time you tap Record, a row is added to the table and a point to the graph.
Aim
To model how predation acts as a selection pressure on a variable population, to measure changes in phenotype and allele frequencies over generations, and to explain natural selection.
What to do
- Keep dark volcanic soil, 20 % dark allele, many birds. Look at the beetles: which colour is easier to see?
- Tap Next generation and watch which beetles the birds eat. Read the message and the table.
- Tap Run 10 generations. Describe the change in the percentage of dark beetles and the frequency of D.
- Do light beetles disappear completely? Use the genotype counts (Dd) to explain.
- Change the soil to light sand and run 10 more generations. What happens?
- Start again with few birds, then very many birds. How does the strength of selection change the speed?
Results
Questions
What is natural selection?
The process by which individuals with features that make them better adapted to their environment survive and reproduce more, passing on their alleles, so these features become more common over generations.
What is the selection pressure in this model?
Predation by birds that hunt by sight.
Why must there be variation for natural selection to happen?
If all beetles were the same, all would have the same chance of survival and nothing would be selected.
Why does the light allele remain in the population on dark soil?
It is recessive, so it is carried hidden in Dd beetles, which are dark and survive.
Give a real example of natural selection observed in a short time.
Antibiotic resistance in bacteria, insecticide resistance in mosquitoes, or the peppered moth in industrial England.
Is it the individual beetle or the population that evolves?
The population: the frequencies of alleles in the population change; an individual keeps the genes it was born with.
For teachers: expected results and how the model works
Model: 120 beetles; colour gene with D (dark) dominant to d (light). Each generation, beetles that contrast with the soil are eaten with probability 0.25, 0.5 or 0.7 (few, many, very many birds); camouflaged beetles with 0.08, 0.12 or 0.15. Survivors mate at random to give 120 offspring (each parent passes one random allele), so chance (genetic drift) also plays a part and every run is different. Starting at 20 % D on dark soil with many birds, dark beetles usually rise from about 36 % to over 90 % in about 10 generations. Selection against a recessive allele slows down as it becomes rare because most d alleles are hidden in Dd. Switching to light soil reverses the direction of selection.
Exam practice Exam set
National-exam style questions on this simulation (14 marks). Try each one on paper first, then open the marking scheme.
Explain how natural selection could cause a population of beetles living on dark soil to become mostly dark. (5 marks)
Marking scheme: Variation in colour exists in the population (1); light beetles are more visible to birds and are eaten more (1); dark beetles survive (1) and reproduce, passing on the allele for dark colour (1); over many generations the frequency of the dark allele increases (1).
In a population of 120 beetles, 30 are dd (light). Use the Hardy–Weinberg equation to estimate the frequency of the D allele. (3 marks)
Marking scheme: q² = 30 ÷ 120 = 0.25 (1); q = 0.5 (1); p = 1 − 0.5 = 0.5 (1).
Explain why the overuse of antibiotics leads to resistant bacteria. (4 marks)
Marking scheme: Mutation produces a few resistant bacteria (1); the antibiotic kills the non-resistant ones (1); resistant bacteria survive and multiply without competition (1); the resistance allele becomes common (1).
Distinguish between natural selection and artificial selection. (2 marks)
Marking scheme: Natural selection: the environment decides which organisms survive and reproduce (1); artificial selection: humans choose which organisms breed, e.g. cattle for milk (1).
Donat Sciences and MathsBiology · Virtual lab worksheet
School: ........................................ Name: ................................ Class: ........ Date: ............
Natural selection: beetle colour, camouflage and birds
Aim: To model how predation acts as a selection pressure on a variable population, to measure changes in phenotype and allele frequencies over generations, and to explain natural selection.
Apparatus (real laboratory): coloured paper dots or beans on light and dark cloth, a stopwatch and “predator” learners.
What to do (with the simulation on www.donatstem.co.rw)
- Keep dark volcanic soil, 20 % dark allele, many birds. Look at the beetles: which colour is easier to see?
- Tap Next generation and watch which beetles the birds eat. Read the message and the table.
- Tap Run 10 generations. Describe the change in the percentage of dark beetles and the frequency of D.
- Do light beetles disappear completely? Use the genotype counts (Dd) to explain.
- Change the soil to light sand and run 10 more generations. What happens?
- Start again with few birds, then very many birds. How does the strength of selection change the speed?
Results
| # | Generation | Dark beetles | Light beetles | Dark (%) | Frequency of D |
|---|
| 1 | | | | | |
| 2 | | | | | |
| 3 | | | | | |
| 4 | | | | | |
| 5 | | | | | |
| 6 | | | | | |
| 7 | | | | | |
| 8 | | | | | |
| 9 | | | | | |
| 10 | | | | | |
| 11 | | | | | |
| 12 | | | | | |
| 13 | | | | | |
| 14 | | | | | |
Graph
Plot the percentage of dark beetles against generation. Mark when the soil was changed.
Questions
- What is natural selection? [2]
- What is the selection pressure in this model? [2]
- Why must there be variation for natural selection to happen? [2]
- Why does the light allele remain in the population on dark soil? [2]
- Give a real example of natural selection observed in a short time. [2]
- Is it the individual beetle or the population that evolves? [2]
- Explain how natural selection could cause a population of beetles living on dark soil to become mostly dark. [5]
- In a population of 120 beetles, 30 are dd (light). Use the Hardy–Weinberg equation to estimate the frequency of the D allele. [3]
- Explain why the overuse of antibiotics leads to resistant bacteria. [4]
- Distinguish between natural selection and artificial selection. [2]
Donat Sciences and MathsBiology · Virtual lab worksheet
School: ........................................ Name: ................................ Class: ........ Date: ............
Marking scheme: Natural selection: beetle colour, camouflage and birds
Expected results
Model: 120 beetles; colour gene with D (dark) dominant to d (light). Each generation, beetles that contrast with the soil are eaten with probability 0.25, 0.5 or 0.7 (few, many, very many birds); camouflaged beetles with 0.08, 0.12 or 0.15. Survivors mate at random to give 120 offspring (each parent passes one random allele), so chance (genetic drift) also plays a part and every run is different. Starting at 20 % D on dark soil with many birds, dark beetles usually rise from about 36 % to over 90 % in about 10 generations. Selection against a recessive allele slows down as it becomes rare because most d alleles are hidden in Dd. Switching to light soil reverses the direction of selection.
Answers
- What is natural selection? [2]
The process by which individuals with features that make them better adapted to their environment survive and reproduce more, passing on their alleles, so these features become more common over generations.
- What is the selection pressure in this model? [2]
Predation by birds that hunt by sight.
- Why must there be variation for natural selection to happen? [2]
If all beetles were the same, all would have the same chance of survival and nothing would be selected.
- Why does the light allele remain in the population on dark soil? [2]
It is recessive, so it is carried hidden in Dd beetles, which are dark and survive.
- Give a real example of natural selection observed in a short time. [2]
Antibiotic resistance in bacteria, insecticide resistance in mosquitoes, or the peppered moth in industrial England.
- Is it the individual beetle or the population that evolves? [2]
The population: the frequencies of alleles in the population change; an individual keeps the genes it was born with.
- Explain how natural selection could cause a population of beetles living on dark soil to become mostly dark. [5]
Variation in colour exists in the population (1); light beetles are more visible to birds and are eaten more (1); dark beetles survive (1) and reproduce, passing on the allele for dark colour (1); over many generations the frequency of the dark allele increases (1).
- In a population of 120 beetles, 30 are dd (light). Use the Hardy–Weinberg equation to estimate the frequency of the D allele. [3]
q² = 30 ÷ 120 = 0.25 (1); q = 0.5 (1); p = 1 − 0.5 = 0.5 (1).
- Explain why the overuse of antibiotics leads to resistant bacteria. [4]
Mutation produces a few resistant bacteria (1); the antibiotic kills the non-resistant ones (1); resistant bacteria survive and multiply without competition (1); the resistance allele becomes common (1).
- Distinguish between natural selection and artificial selection. [2]
Natural selection: the environment decides which organisms survive and reproduce (1); artificial selection: humans choose which organisms breed, e.g. cattle for milk (1).