CB4.3 — Selective breeding and genetic engineering (Edexcel 1SC0 — Higher tier)

Selective breeding

Humans select organisms with desirable traits and breed them together over many generations. Examples:

• Cattle: selected for high milk yield or muscle mass.
• Wheat: selected for disease resistance and high grain yield.
• Dogs: selected for temperament and physical traits.

Disadvantages: reduced genetic variation → increased susceptibility to disease; inbreeding can lead to genetic defects.

Genetic engineering

Transfer of a gene from one organism's DNA into another organism's DNA.

Process:

1. Identify and cut out the desired gene using restriction enzymes.
2. Cut open a vector (usually a plasmid) with the same restriction enzymes → complementary sticky ends.
3. Insert the gene into the vector using ligase enzyme.
4. Introduce the recombinant plasmid into the host organism.
5. Host organism expresses the new gene.

Examples:

• Insulin production: human insulin gene inserted into bacteria → bacteria produce human insulin for diabetics.
• GM crops: herbicide-resistant or drought-tolerant crops; crops producing their own pesticide (Bt toxin).
• Golden Rice: contains gene for beta-carotene production → helps prevent vitamin A deficiency.

Ethical concerns: unknown long-term effects; escape of GM genes into wild populations; "playing God"; biodiversity reduction.