Exam Tips: DNA and the Genome

Base pair rule: Learn "AT CG" as a single unit. A always pairs with T (and never with C or G). C always pairs with G. If given one strand, write out the complementary strand base by base.

Hierarchy matters: Examiners test whether you can place terms in the correct order of scale: bases → nucleotides → DNA → gene → chromosome → nucleus → cell. Avoid reversing the order.

Gene vs genome distinction: "Gene" is one instruction; "genome" is the entire instruction set. Never use them interchangeably. When asked to define "genome", say "all the genetic material of an organism", not just "all the genes".

Link DNA to protein: For any explain question about how DNA determines a characteristic, always include the chain: base sequence → amino acid sequence → protein shape → function → characteristic.

Higher tier: The Human Genome Project is a frequent context for evaluate questions. Be ready to state both benefits (disease identification, personalised medicine) and ethical concerns (privacy, discrimination).

Alleles vs genes: A gene is the instruction (e.g., hair colour gene); an allele is the version of that instruction (e.g., black hair allele, blonde hair allele). Different alleles produce different phenotypes for the same characteristic.

Edexcel mark scheme language: Edexcel mark schemes use "Accept..." and "Allow..." to credit alternative correct phrasings. This means plain-English descriptions of base pairing or protein synthesis will be accepted alongside technical terminology. However, never use vague language — always be specific about WHERE each process happens (nucleus for transcription, ribosome for translation).