AQA GCSE (9-1) Biology: Genetics and Evolutio

Key Takeaways for Genetics and Evolution

1. Theory of Evolution by Natural Selection

• Key Scientist: Charles Darwin (supported by Alfred Russel Wallace).
• Main Idea: Species evolve over time from a common ancestor through:
  1. Variation in traits within a population.
  2. Competition for limited resources.
  3. Survival of the fittest: Organisms with advantageous traits survive and reproduce.
  4. Inheritance of beneficial traits to offspring.
  5. Over time, new species form.
• Example: Darwin’s finches on the Galapagos Islands.
  • Different beak shapes evolved to suit food sources (e.g., seeds vs. insects).
• Key Equation: Probability of traits in Mendel’s pea plants (e.g., yellow vs. green seeds):
  • Cross Yy × Yy: Phenotypic ratio = 3:1 (75% yellow, 25% green).
  YyYYYYyyYyyyYy​YYYYy​yYyyy​​

Tip: Use VISTA to remember natural selection steps: Variation, Inheritance, Selection, Time, Adaptation.

2. Speciation

• Definition: Formation of new species due to reproductive isolation.
• Types:
  • Allopatric speciation: Geographical separation (e.g., Wallace Line divides species in Australia and Southeast Asia).
  • Example: Three-spined stickleback fish diverged during the ice age.

Key Rule: A species is defined as organisms that can interbreed to produce fertile offspring.

3. Evidence for Evolution

• Fossils:
  • Formation: Preservation in rocks (no oxygen, mineral replacement, trace fossils).
  • Examples:
    • Archaeopteryx (reptile-bird transition).
    • Horse hooves evolving from marsh-adapted feet.
  • Limitation: Fossil record has gaps (soft tissues rarely fossilise).
• Antibiotic Resistance:
  • Example: MRSA (methicillin-resistant Staphylococcus aureus).
  • Process:
    1. Random mutation → resistance.
    2. Antibiotics kill non-resistant bacteria.
    3. Resistant bacteria survive and reproduce.

Tip: Link antibiotic resistance to natural selection steps.

4. Genetics (Mendel’s Laws)

• Key Scientist: Gregor Mendel (pea plant experiments).
• Key Terms:
  • Dominant allele (e.g., Y for yellow seeds).
  • Recessive allele (e.g., y for green seeds).
• Example: Crossing two heterozygous (Yy) plants:
  • Genotypic ratio: 1 YY : 2 Yy : 1 yy.
  • Phenotypic ratio: 3 yellow : 1 green.

Common Mistake: Blended inheritance (incorrect) vs. Mendelian inheritance (correct).

5. Lamarck’s Discredited Theory

• Inheritance of Acquired Characteristics: Traits developed during an organism’s lifetime (e.g., giraffe stretching neck) are passed to offspring.
• Why Discredited: No genetic basis (traits not coded in DNA).
• Modern Insight: Epigenetics (gene expression changes) may support partial validity.

6. Extinction

• Causes:
  • Environmental changes (e.g., ice age).
  • New predators/diseases (e.g., dodo hunted by humans).
  • Competition (e.g., invasive species).
  • Mass extinctions (e.g., dinosaurs from asteroid impact).

Example: Holocene extinction (current human-driven extinction).

7. Exam Tips

• Define Terms Clearly: E.g., “speciation” = forming new species via isolation.
• Use Examples: Always link theories to examples (e.g., MRSA for natural selection).
• Practice Calculations: Mendel’s ratios (use Punnett squares).
• Evaluate Evidence: Discuss strengths/weaknesses of fossil record.

Trick: For essay questions, structure answers with PEEL (Point, Evidence, Explain, Link).

50 GCSE Questions on Genetics and Evolution

Section A: Theory of Evolution

1. Name the scientist who first described evolution by natural selection.
2. What islands did Darwin visit to develop his theory?
3. Describe two adaptations of Darwin’s finches.
4. Explain why Darwin delayed publishing his theory.
5. What term describes organisms evolving from a shared ancestor?

Section B: Speciation

6. Define speciation.
7. What is the Wallace Line, and why is it significant?
8. Give an example of allopatric speciation.
9. How does geographical isolation lead to new species?
10. What defines a species?

Section C: Genetics (Mendel)

11. Who is the founder of modern genetics?
12. What organism did Mendel study, and what traits did he examine?
13. A pea plant with genotype Yy is crossed with another Yy. Calculate the phenotypic ratio.
14. Explain why Mendel’s work was initially ignored.
15. What is the difference between dominant and recessive alleles?

Section D: Evidence for Evolution

16. How do fossils provide evidence for evolution?
17. Name a fossil that shows the transition between reptiles and birds.
18. Explain why the fossil record is incomplete.
19. How does antibiotic resistance in bacteria support evolution?
20. What is MRSA, and why is it dangerous?

Section E: Lamarck’s Theory

21. What is the inheritance of acquired characteristics?
22. Give an example Lamarck used to explain giraffes’ long necks.
23. Why was Lamarck’s theory discredited?
24. How might modern epigenetics support parts of Lamarck’s ideas?

Section F: Extinction

25. Define extinction.
26. Name a species hunted to extinction by humans.
27. What caused the mass extinction of dinosaurs?
28. Why are extinction rates increasing today?
29. What is the Holocene extinction?

Section G: Fossil Formation

30. Describe three ways fossils form.
31. Why are peat bogs effective at preserving remains?
32. How do scientists estimate the age of fossils?

Section H: Co-evolution

33. What is co-evolution?
34. Describe the relationship between Darwin’s orchid and the moth.
35. How do hummingbirds and flowers co-evolve?

Section I: Modern Examples

36. What is experimental evolution?
37. How did the rough-skinned newt and garter snake co-evolve?

Section J: Application & Analysis

38. Explain how Darwin’s finches support natural selection.
39. Compare Lamarck’s and Darwin’s theories.
40. Why might antibiotic resistance become a global crisis?
41. Evaluate the strengths and weaknesses of the fossil record.
42. How does Mendel’s work underpin modern genetics?

Section K: Terminology

43. Define natural selection.
44. What is creationism?
45. What does MRSA stand for?
46. Define mass extinction.
47. What is a common ancestor?
48. What is blended inheritance?
49. Define epigenetics.
50. What is uniformitarianism?

Detailed Answers

1. Charles Darwin (and Alfred Russel Wallace).
2. Galapagos Islands (off Chile).
   • Long, thin beaks for insects.
   • Stubby beaks for seeds.
3. Darwin delayed due to societal pressure (religious beliefs) and lack of evidence for inheritance mechanisms.
4. Common ancestor.
5. Speciation: Formation of new species via reproductive isolation.
6. Wallace Line: Boundary in SE Asia dividing Australian and Asian species due to evolution in isolation.
7. Three-spined stickleback fish diverged during ice age isolation.
8. Isolated populations adapt differently → accumulate genetic differences → cannot interbreed.
9. A species can interbreed to produce fertile offspring.
10. Gregor Mendel.
11. Pea plants; traits included seed colour (yellow/green) and flower colour (purple/white).
12. Phenotypic ratio: 3:1 (75% yellow, 25% green).

YyYYYYyyYyyyYy​YYYYy​yYyyy​​

14. Scientists believed in blended inheritance (traits mix, not discrete).
15. Dominant (expressed as Y) masks recessive (y).
16. Fossils show gradual changes (e.g., horse hooves shrinking as marshes dried).
17. Archaeopteryx (reptilian teeth, bird-like feathers).
18. Soft tissues rarely fossilise; many fossils destroyed.
19. Resistant bacteria survive antibiotics → reproduce → resistance spreads (natural selection).
20. Methicillin-resistant Staphylococcus aureus; resistant to antibiotics, deadly in hospitals.
21. Traits acquired in an organism’s lifetime (e.g., giraffe’s stretched neck) inherited.
22. Giraffes stretched necks to reach leaves → offspring inherit longer necks.
23. No genetic basis (DNA not altered by environment).
24. Epigenetics shows environment can switch genes on/off (not DNA change).
25. Extinction: Permanent loss of a species.
26. Dodo (Mauritius, 17th century).
27. Asteroid impact causing climate change.
28. Habitat destruction, pollution, invasive species (human activity).
29. Current mass extinction caused by human activity.
    • Preservation without decay (peat bogs).

• Mineral replacement.
• Trace fossils (footprints).

31. Low oxygen and acidic water prevent decay.
32. Rock layers (older fossils deeper).
33. Co-evolution: Two species evolve in response to each other (e.g., predator-prey).
34. Orchid evolved long spur → moth evolved long proboscis.
35. Flowers: bright colours, digestible nectar. Hummingbirds: long beaks.
36. Studying evolution in fast-reproducing organisms (e.g., E. coli over 50,000 generations).
37. Newt evolved toxin → snake evolved resistance → newt evolved stronger toxin.
38. Finches’ beak shapes matched food sources → natural selection favoured advantageous traits.
39. Lamarck: Acquired traits inherited. Darwin: Traits inherited via genes, selected by environment.
40. Overuse of antibiotics → resistant strains spread → untreatable infections.
41. Strengths: Shows gradual change. Weaknesses: Gaps, bias toward hard-bodied organisms.
42. Mendel showed traits inherited via discrete units (genes), not blending.
43. Natural selection: Advantageous traits → survival → passed to offspring.
44. Creationism: Belief that a deity created life.
45. Methicillin-resistant Staphylococcus aureus.
46. Mass extinction: Many species die out rapidly (e.g., dinosaurs).
47. Common ancestor: Organism from which multiple species evolved.
48. Blended inheritance: Discredited idea that traits mix (e.g., red + white flowers → pink).
49. Epigenetics: Study of gene expression changes (not DNA sequence).
50. Uniformitarianism: Geological changes occur slowly over time (Hutton’s theory).

Tip: For calculations, always show Punnett squares and ratios. Use examples like MRSA or Darwin’s finches to contextualise answers!