Exam Tips: Selective Breeding

Always include "over many generations": This phrase appears in virtually every mark scheme (both AQA and Edexcel) for selective breeding process questions. Without it, you will likely lose a mark.

Link the disadvantage to the mechanism: Saying "it reduces genetic variation" alone is often not enough. Explain why this is a problem: "If all individuals have similar alleles, a disease that one individual cannot resist will affect the entire population."

Selective breeding does not create new genes: A common error is saying breeders "give" organisms new genes. Breeders only select from variation that already exists. This is the key difference from genetic engineering.

Be specific with examples: Generic answers score less than specific ones. "Cows selected for milk yield" scores better than "animals selected for good traits."

Edexcel "Suggest" on novel scenarios: Edexcel 1BI0/1 may give you a breeding scenario you have never seen and ask you to "Suggest" which individuals should be selected. Apply the SSBR steps to the context: identify the desired trait from the stimulus, select individuals showing it most strongly, breed them together, repeat over generations. Marks are awarded for applying the process to the specific context — not for reciting the process generically.