DNA and the Genome: overview of SQA Higher Biology Area 1

DNA and the Genome is the first of the three areas of SQA Higher Biology. It explores the molecular basis of inheritance: how genetic information is stored, copied, expressed, changed and used to specialise cells, and how comparing genomes reveals evolution. This page maps the six key areas and shows how they connect.

The six key areas

Structure of DNA

DNA is a double-stranded, antiparallel molecule of nucleotides with complementary base pairing (A-T, G-C) and a sugar-phosphate backbone. The genome is organised differently in prokaryotes (circular chromosome plus plasmids) and eukaryotes (linear chromosomes in the nucleus).

Replication of DNA

DNA polymerase copies each strand using primers, free nucleotides and ATP, making a continuous leading strand and a fragmented lagging strand. PCR amplifies a target sequence in the laboratory.

Gene expression

Transcription makes a primary transcript that is spliced into mature mRNA; translation builds a polypeptide at a ribosome using tRNA. Alternative splicing lets one gene code for several proteins.

Mutations

Single gene mutations (substitution, insertion, deletion) and chromosome structure mutations change the genome and provide the variation on which evolution acts.

Evolution and genomic sequencing

Natural selection (stabilising, directional, disruptive), gene transfer, genetic drift and isolation drive evolution and speciation, and genomic sequencing builds phylogenetic trees.

Cellular differentiation

Cells specialise by expressing only the genes they need; stem cells are unspecialised cells with therapeutic and research uses, and cancer cells escape normal control.

How to study Area 1

1. Learn the terminology exactly. Higher rewards precise wording such as primary transcript, splicing, antiparallel and pluripotent.
2. Follow the flow of information. Structure, replication, expression and mutation form one connected story; link the key areas rather than learning them in isolation.
3. Practise applying ideas to data. Many marks come from interpreting unfamiliar sequences, family trees and phylogenetic data.
4. Use the question paper style. Drill SQA past-paper items, which are written directly from these key areas.

For the official course specification

The SQA publishes the full Higher Biology course specification, specimen and past papers, and marking instructions at sqa.org.uk. Always revise from the current specification and SQA past papers.