BIOLOGY WITH HAMZA · MDCAT REVISION
Evolution
Name: ____________________ Date: ______________
Recall first. Check second. Return to the ideas you missed.
Choose “Save as PDF” in your browser’s print dialog to download this chapter sheet.
Learning targets
- Distinguish Lamarck's mechanism from Darwin's natural selection.
- Explain variation, selection pressure and differential reproduction.
- Connect evidence from fossils, homology, biogeography and molecular data.
Core notes
- Populations evolve; individuals are selected within a generation.
- Lamarck proposed acquired inheritance, while Darwin emphasised selection of heritable variation.
- Natural selection changes variant frequencies through differential reproduction.
- Fossil, anatomical, geographic and molecular evidence support common descent.
Read, cover and redraw
Individuals differ in heritable traits.
The environment affects survival and reproduction.
Some variants leave more offspring.
Associated alleles become more common.
Written recall
1. Why is antibiotic resistance not evidence that bacteria mutate because they need to survive?
2. What is the difference between homologous and analogous structures?
Apply the idea
1. Antibiotic-resistant colonies appear after a bacterial population is exposed to an antibiotic. Which additional observation most strongly supports selection of pre-existing resistance?
- Resistant variants were detectable in the population before treatment
- All bacteria were larger after treatment
- The antibiotic changed colour
- Only treated cultures were ever examined
My answer: _____ Reason: ____________________________________
2. A population contains 30 AA, 50 Aa and 20 aa individuals. What is the frequency of allele A?
- 0.30
- 0.55
- 0.50
- 0.80
My answer: _____ Reason: ____________________________________
3. Two small isolated populations start with the same allele frequencies. With no consistent fitness differences, their frequencies diverge randomly over generations. The most direct explanation is:
- Directional selection in the same direction
- Identical gene flow into both populations
- Genetic drift
- A purposeful response to environmental need
My answer: _____ Reason: ____________________________________
Answer key
Cover this section while attempting the questions.
Written recall
1. Variation arises independently of need; antibiotic exposure selects resistant variants that already exist or were acquired.
2. Homologous structures share underlying ancestry even if functions differ; analogous structures perform similar functions but evolved independently.
Applied questions
1. A — Detecting resistance before exposure supports variation preceding selection. Antibiotic treatment then favours resistant survivors; it need not create the particular adaptive variant.
2. B — There are 200 alleles at this locus. A alleles total 2×30 + 50 = 110, so their frequency is 110/200 = 0.55.
3. C — Chance differences in which individuals reproduce can change allele frequencies, especially in small populations. This is genetic drift rather than a directed response to need.