Key Takeaways for Variation, Selective Breeding, Genetic Engineering & Cloning

1. Variation

Definition: Differences between individuals within a species or between species.

Types of Variation

  1. Continuous Variation:
    • Data exists on a spectrum (e.g., height, weight).
    • Example: Human height ranges from 150 cm to 190 cm.
    • Graph: Line graph or histogram (bars touch for grouped data).
    • Normal Distribution:
      • Bell-shaped curve; most data clustered around the mean.
      • Formula: f(x)=1σ2πe−(x−μ)22σ2f(x)=σ2π​1​e−2σ2(x−μ)2​ (shape described, not calculated at GCSE).
  2. Discontinuous Variation:
    • Distinct categories with no intermediates (e.g., blood groups, eye colour).
    • Example: Blood type can only be A, B, AB, or O.
    • Graph: Bar chart (gaps between bars).

Causes of Variation:

  • Genetic: Inherited via genes (e.g., cystic fibrosis, eye colour).
  • Environmental: Influenced by surroundings (e.g., scars, suntans).
  • Combination: Both genetics and environment (e.g., height influenced by genes and diet).

Tip: To remember types, ask: Can you measure it in a range? (Continuous) or Is it fixed categories? (Discontinuous).

2. Selective Breeding

Definition: Artificially selecting organisms with desired traits to breed.

Process:

  1. Choose parents with desired traits (e.g., large size in cows).
  2. Breed them; repeat over generations.

Examples:

  • Dogs: Great Danes (bred for size), Golden Retrievers (bred for temperament).
  • Crops: Drought-resistant wheat, disease-resistant maize.

Risks:

  • Inbreeding: Reduces genetic diversity, increasing risk of genetic disorders (e.g., hip dysplasia in pugs).
  • Gene Pool: Smaller gene pools limit adaptability to environmental changes.

Key Term: Artificial selection = Selective breeding.

Tip: Link examples to real-world issues (e.g., Belgian Blue cattle bred for muscle mass).

3. Genetic Engineering (GM)

Definition: Transferring genes between organisms to produce transgenic organisms.

Process:

  1. Isolate desired gene (e.g., carotene gene from corn).
  2. Insert into vector (e.g., plasmid in bacteria).
  3. Transfer into host organism (e.g., rice embryo).

Examples:

  • Golden Rice: Engineered with carotene to prevent vitamin A deficiency.
  • Insulin-Producing Bacteria: Human insulin gene inserted into E. coli.
  • Glow-in-the-Dark Rabbits: Jellyfish GFP gene inserted into rabbit DNA.

Ethical Issues:

  • For: Addresses food shortages/medical needs (e.g., drought-resistant crops).
  • Against: Religious objections, gene transfer to wild species (e.g., herbicide-resistant weeds).

Key Terms:

  • Plasmid: Circular DNA in bacteria used as a vector.
  • Vector: Carrier of DNA (e.g., plasmid or virus).

Tip: Use flow diagrams to visualise gene transfer steps.

4. Cloning

Definition: Producing genetically identical organisms.

Methods:

  1. Tissue Culture:
    • Plant cells grown in nutrient agar (e.g., cloning carrots).
    • Example: Orchids cloned for identical flowers.
  2. Embryo Splitting:
    • Splitting embryos to create twins (used in cattle farming).
  3. Adult Cell Cloning (Dolly the Sheep):
    • Steps:
      1. Remove diploid nucleus from udder cell.
      2. Insert into enucleated egg cell.
      3. Stimulate mitosis with electric shock.
      4. Implant into surrogate mother.

Ethical Concerns:

  • Health risks in clones (e.g., Dolly’s early death from lung disease).
  • Illegal in humans due to moral objections.

Tip: Memorise Dolly’s process using acronyms (e.g., S.N.I.P.: Surrogate, Nucleus, Implant, Pregnancy).

5. Data Handling & Graphs

Rules for Graphs:

  • Line Graph: Continuous data (e.g., height over time).
  • Bar Chart: Discontinuous data (e.g., blood groups).
  • Histogram: Continuous grouped data (e.g., mass ranges).

Example Calculation:

  • For blood type O donors (Figure 15.14):
    Total donors = 112, Type O = 70.
    Percentage = 70112×100≈62.5%11270​×100≈62.5% (rounded to 63%).

Trick: Use C for Continuous = Curved line graph; D for Discontinuous = Distinct bars.

Revision Tips:

  • Flashcards: Create cards for key terms (e.g., transgenic, inbreeding).
  • Case Studies: Link examples to processes (e.g., Dolly → adult cell cloning).
  • Practice Questions: Attempt graph plotting (e.g., hand span vs. foot length scatter graph).

50 GCSE Biology Questions on Variation, Selective Breeding, Genetic Engineering & Cloning

(Answers detailed at the end)

Variation

  1. Define variation.
  2. Give two examples of continuous variation.
  3. What is discontinuous variation? Provide an example.
  4. Explain why height is an example of both genetic and environmental variation.
  5. How does normal distribution appear on a graph?
  6. Calculate the percentage of 11-year-olds in Student B’s data (Table 15.2) with a mass of 50–54 kg.
  7. Why are bar charts used for discontinuous data?
  8. Name two genetic factors that cause variation.
  9. Give two environmental factors that cause variation.
  10. What term describes data forming a bell-shaped curve?

Selective Breeding

  1. Define selective breeding.
  2. Explain how Friesian cows were selectively bred.
  3. What is inbreeding? Why is it risky?
  4. Describe how dogs were selectively bred from wolves.
  5. Name a crop that has been selectively bred for disease resistance.
  6. What is a gene pool?
  7. Why do pug dogs have a small gene pool?
  8. Give two traits farmers might selectively breed in cattle.
  9. What is another term for selective breeding?
  10. Why might Belgian Blue cattle be controversial?

Genetic Engineering

  1. Define genetic engineering.
  2. What is a transgenic organism?
  3. Explain how golden rice was genetically modified.
  4. Describe how the glow-in-the-dark rabbit was created.
  5. Why is herbicide-resistant soya controversial?
  6. What is a plasmid?
  7. How are plasmids used in genetic engineering?
  8. Name a protein produced by genetically engineered sheep.
  9. Why is human genetic engineering illegal?
  10. Explain one ethical objection to GM crops.

Cloning

  1. Define cloning.
  2. Outline the steps taken to clone Dolly the sheep.
  3. Why did Dolly’s face remain pale despite her surrogate mother’s black face?
  4. What is tissue culture? Give an example.
  5. How does embryo splitting increase livestock numbers?
  6. Why is cloning humans illegal?
  7. Name two animals cloned before Dolly.
  8. What hormone is used in plant cloning via tissue culture?
  9. Why might cloned animals die prematurely?
  10. Explain the purpose of using aseptic technique in plant cloning.

Data Handling & Graphs

  1. When should a histogram be used instead of a bar chart?
  2. Plot Student A’s data (Table 15.1) as a histogram.
  3. Calculate the mean mass for Student B’s data (Table 15.2).
  4. Why is shoe size not ideal for measuring foot length variation?
  5. What type of graph would you use to display eye colour data?

Application & Ethics

  1. Suggest why cats have fewer breeds than dogs.
  2. Explain why reduced genetic variation is dangerous for a species.
  3. Why might religious groups oppose genetic engineering?
  4. How could GM crops address food shortages in Africa?
  5. Evaluate one risk of using embryo transfer in farming.

Detailed Answers

  1. Variation: Differences between individuals of the same species or between species.
  2. Continuous variation examples: Height (e.g., 150–190 cm), weight, hand span.
  3. Discontinuous variation: Distinct categories with no intermediates. Example: Blood groups (A/B/AB/O).
  4. Height: Genetic (inherited from parents) + Environmental (diet, calcium intake).
  5. Normal distribution: Bell-shaped curve; most data near mean, fewer at extremes. Formula: f(x)=1σ2πe−(x−μ)22σ2f(x)=σ2π​1​e−2σ2(x−μ)2​.
  6. Percentage calculation:
    • Total = 11 + 24 + 39 + 85 + 45 + 21 + 15 = 240
    • 50–54 kg frequency = 85
    • Percentage = 85240×100≈35.4%24085​×100≈35.4%.
  7. Bar charts: Discontinuous data has distinct categories; gaps between bars show no intermediates.
  8. Genetic factors: Eye colour, blood group, cystic fibrosis.
  9. Environmental factors: Scars, suntans, tattoos.
  10. Normal distribution.
  1. Selective breeding: Artificially breeding organisms with desired traits.
  2. Friesian cows: Bred for high milk yield (less creamy than Jersey cows).
  3. Inbreeding: Breeding closely related organisms; risks genetic disorders (e.g., hip dysplasia in pugs).
  4. Dogs from wolves: Selected for size (Great Dane), temperament (Golden Retriever), or utility (German Shepherd).
  5. Disease-resistant maize.
  6. Gene pool: Total genetic diversity in a population.
  7. Pugs: Inbreeding reduced gene pool to equivalence of 50 animals.
  8. Cattle traits: Muscle mass (Belgian Blue), milk yield, drought resistance.
  9. Artificial selection.
  10. Belgian Blue controversy: Ethical concerns over extreme muscle growth affecting animal welfare.
  1. Genetic engineering: Transferring genes between species to create transgenic organisms.
  2. Transgenic organism: Contains genes from another species (e.g., glow-in-the-dark rabbit).
  3. Golden rice: Carotene gene from corn inserted into rice to combat vitamin A deficiency.
  4. Glow-in-the-dark rabbit: Jellyfish GFP gene inserted into rabbit embryo DNA.
  5. Herbicide-resistant soya: Risk of gene transfer to weeds, creating “superweeds”.
  6. Plasmid: Circular bacterial DNA used as a vector in genetic engineering.
  7. Plasmid use: Cut with enzymes, insert gene (e.g., insulin), transfer to host.
  8. Sheep proteins: Blood-clotting factors for haemophilia treatment.
  9. Illegal in humans: Ethical and safety concerns.
  10. Ethical objection: Religious beliefs against “playing God” or gene contamination.
  1. Cloning: Producing genetically identical organisms (e.g., Dolly the sheep).
  2. Dolly’s cloning steps:
    • Diploid nucleus from udder cell inserted into enucleated egg.
    • Electric shock triggers mitosis.
    • Embryo implanted into surrogate mother.
  3. Dolly’s face colour: DNA came from original pale-faced sheep, not surrogate.
  4. Tissue culture: Growing plants from cells in nutrient agar (e.g., cloned carrots).
  5. Embryo splitting: Splitting embryos pre-implantation to create twins.
  6. Illegal human cloning: Ethical issues, health risks (e.g., premature aging).
  7. Cloned animals: Tadpoles (1952), mice (1986).
  8. Plant hormone: Auxins or cytokinins.
  9. Premature death: Cloned DNA may have shortened telomeres (e.g., Dolly’s lung disease).
  10. Aseptic technique: Prevents microbial contamination of plant tissue.
  1. Histogram vs. bar chart: Histograms for continuous data (e.g., mass ranges); bars touch.
  2. Student A’s histogram:
    • X-axis: Mass groups (35–39, 40–44, etc.).
    • Y-axis: Frequency (1, 2, 4, 5, 9, 6, 3). Bars touch.
  3. Mean mass calculation:
    • Midpoints: 37, 42, 47, 52, 57, 62, 67.5
    • Mean=(37×11)+(42×24)+⋯+(67.5×15)240≈52.3 kgMean=240(37×11)+(42×24)+⋯+(67.5×15)​≈52.3kg.
  4. Shoe size: Discontinuous (whole numbers only); foot length in cm is continuous.
  5. Eye colour graph: Bar chart (discrete categories).
  1. Fewer cat breeds: Bred primarily for pest control, not diverse traits like dogs.
  2. Reduced variation: Less adaptability to environmental changes/diseases.
  3. Religious objections: Belief that genetic engineering interferes with natural creation.
  4. GM crops in Africa: Drought-resistant maize improves food security.
  5. Embryo transfer risk: Overuse reduces genetic diversity, increasing disease susceptibility.