Variation and Evolution

• What are the two main causes of variation in a species?

  Genetic causes and environmental causes.
• What is continuous variation? Give an example.

  Variation with a full range of values and no distinct categories, e.g. height.
• What is discontinuous variation? Give an example.

  Variation with distinct categories, e.g. blood group.
• How does sexual reproduction cause genetic variation?

  By combining genes from two parents, leading to genetically different offspring.
• What is asexual reproduction?

  Reproduction from a single parent producing genetically identical offspring (clones).
• What is a mutation?

  A random change in DNA that can result in a new gene.
• What are the possible effects of mutations?

  Most have no effect, some are harmful, and a few are beneficial.
• What can increase the rate of mutation?

  Ionising radiation and some chemicals.
• What causes cystic fibrosis?

  A mutation in a recessive allele inherited from both parents.
• How is cystic fibrosis inherited?

  It is inherited when a person receives two copies of the faulty recessive allele.
• What does a carrier of cystic fibrosis have?

  One faulty allele and one normal allele — they do not show symptoms.
• What is gene therapy?

  A treatment that involves inserting a healthy gene to replace a faulty one.
• What are some issues with gene therapy?

  Ethical concerns, effectiveness, cost, and possible side effects.
• What is heritable variation?

  Genetic variation that can be passed from parents to offspring.
• Why is heritable variation important in evolution?

  It provides the basis for natural selection and evolution.
• What is natural selection?

  The process where individuals with advantageous traits survive, reproduce, and pass on their genes.
• How does camouflage help in natural selection?

  Camouflaged individuals are less likely to be seen by predators and more likely to survive.
• Why are models of camouflage limited?

  They simplify complex ecosystems and may not include behaviour or other factors.
• What happens if organisms can’t adapt to environmental changes?

  They may become extinct.
• Who proposed the theory of natural selection?

  Charles Darwin and Alfred Russell Wallace.
• What are examples of ongoing evolution?

  Antibiotic resistance in bacteria, pesticide resistance, and warfarin resistance in rats.
• How does resistance (e.g. to antibiotics) evolve?

  Through mutations; resistant individuals survive and reproduce, spreading the trait.
• What is the human genome?

  The complete set of genes in a human.
• How is understanding the human genome useful for medicine?

  It helps identify genetic disorders, personalise treatments, and develop new therapies.