Summary

GCSE Biology – Evolution & Genetics (Triple Science)

1. Darwin & Wallace – Evolution by Natural Selection

  • Charles Darwin (1859): theory of evolution by natural selection.

  • Alfred Russel Wallace independently developed the same idea.

  • Both published findings in 1858.

  • Natural selection = organisms with beneficial characteristics (alleles) survive & reproduce → advantageous alleles passed on.

  • Wallace also studied warning colouration in animals.

Speciation (Triple only)

  • Definition: Formation of new species from an existing one.

  • Process:

    1. Geographical barrier separates population.

    2. No interbreeding → genetic isolation.

    3. Different mutations + natural selection act on each group.

    4. Populations become so different → cannot produce fertile offspring.

  • Result = new species formed.

2. Mendel & Genetics

  • Gregor Mendel (mid-1800s): studied inheritance using pea plants.

  • Discovered:

    • Traits are controlled by “inherited units” (now called genes).

    • Traits are not blended.

    • Some alleles are dominant, others recessive.

  • Work was ignored until after his death.

  • Later discoveries:

    • Genes are located on chromosomes.

    • DNA structure determined (1953).

3. Evidence for Evolution: Fossils

  • Fossils = remains of organisms from millions of years ago found in rocks.

  • Three ways fossils form:

    1. Parts of organism do not decay (no oxygen, water, or too cold).

    2. Hard parts replaced by minerals.

    3. Preserved traces (e.g. footprints, burrows).

Problems

  • Soft-bodied organisms rarely form fossils → record incomplete.

  • Many fossils destroyed by geological activity.

Extinction

  • Definition: No individuals of a species remain alive.

  • Causes:

    • Catastrophic event (e.g. asteroid → dinosaurs).

    • Environmental change (climate, disease, new predator).

    • Competition from new species.

4. Evidence for Evolution: Antibiotic Resistance

  • Bacteria reproduce every 30 minutes → evolve rapidly.

  • Antibiotics kill bacteria (not viruses).

  • Overuse → development of antibiotic-resistant strains (e.g. MRSA).

Process of Resistance

  1. Mutation produces resistant bacterium.

  2. Antibiotic kills non-resistant bacteria.

  3. Resistant bacterium survives & reproduces.

  4. Resistant strain spreads.

Reducing Resistance

  • Doctors: do not prescribe antibiotics for viruses.

  • Patients: complete full course.

  • Restrict use of antibiotics in farming.

  • Develop new antibiotics (slow & expensive).

5. Classification & Evolutionary Trees

  • Carl Linnaeus (1700s): classified organisms based on characteristics.

  • Hierarchy: Kingdom → Phylum → Class → Order → Family → Genus → Species.

    • Mnemonic: King Philip Came Over For Good Soup.

  • Binomial naming system = Genus + species (e.g. Homo sapiens).

Modern Classification – Three Domain System (Carl Woese)

  1. Archaea – primitive bacteria (extreme conditions).

  2. Bacteria – true bacteria (e.g. gut bacteria).

  3. Eukaryota – animals, plants, fungi, protists.

Evolutionary Trees

  • Show relationships between organisms.

  • Built using DNA evidence (living organisms) or fossils (extinct).

6. Cloning (Triple only)

  • Clones = genetically identical organisms.

  • Formed by asexual reproduction (no gametes).

Methods:

  1. Tissue Culture (plants) – small groups of cells grown into new plants.

    • Used for rare plants, plant research, or commercial crops.

  2. Cuttings (plants) – simple, quick method using stem cuttings.

  3. Embryo Transplants (animals) – embryo split into cells → identical offspring.

  4. Adult Cell Cloning (animals)

    • Nucleus removed from egg cell.

    • Nucleus from adult body cell inserted.

    • Electric shock → cell divides into embryo.

    • Embryo implanted into surrogate mother.

    • Example: Dolly the sheep (1996).

Advantages

  • Produce organisms with desirable traits.

  • Preserve endangered species.

  • Medical uses (e.g. mass production of identical animals for research).

Disadvantages

  • Reduced genetic variation → vulnerable to disease.

  • Low success rate, costly.

  • Ethical concerns about animal welfare.