WJEC GCSE Biology 2.4 Variation and Evolution Exam Questions

About WJEC GCSE Biology 2.4 Variation and Evolution

Variation and evolution in Unit 2 explains why individuals differ and how this leads to evolution. You need to separate genetic and environmental causes of variation, distinguish continuous from discontinuous variation, and explain why sexual reproduction gives variation while asexual reproduction gives clones. Mutations, including those caused by ionising radiation, and the inherited condition cystic fibrosis are covered, along with family tree interpretation and gene therapy. The topic then explains natural selection as proposed by Darwin and Wallace, with modern examples such as antibiotic, pesticide and warfarin resistance. Investigating variation is a specified practical, and long answers on natural selection are common.

What you need to know

• Types of variation Variation can be genetic, environmental or both. Continuous variation has a range of values (e.g. height, shown on a histogram); discontinuous variation has distinct categories (e.g. blood group, shown on a bar chart). Investigating variation in organisms is a specified practical.
• Reproduction Sexual reproduction combines gametes from two parents, so offspring are genetically different. Asexual reproduction involves one parent and produces genetically identical clones.
• Mutations Mutations are random changes in genes or chromosomes. Most are harmful or neutral; a few are beneficial. Ionising radiation and some chemicals increase the rate of mutation.
• Cystic fibrosis Cystic fibrosis is caused by a recessive allele, so a child must inherit two copies. Carriers are heterozygous. Interpret family trees to work out genotypes, and discuss issues around gene therapy.
• Natural selection Proposed by Darwin and Wallace: organisms show variation; there is competition; those with better adapted features survive and reproduce; they pass on their alleles; over many generations the population changes. Species become extinct if they cannot adapt quickly enough.
• Evolution today Bacteria evolve antibiotic resistance, insects pesticide resistance and rats warfarin resistance. Knowledge of the human genome is important in medicine, e.g. identifying genes linked to disease.

Common mistakes in 2.4 Variation and Evolution

• Saying animals change or adapt because they need to. Variation already exists through mutation; individuals with useful variations survive and pass on their alleles.
• Writing that bacteria become immune to antibiotics. Bacteria become resistant through a random mutation; immunity refers to the body's defence system.
• Stating that two carriers will have one child in four with cystic fibrosis. There is a 25% chance for each child, independently, however many children they have.
• Mixing up the graphs for variation. Continuous data go on a histogram with touching bars; discontinuous data go on a bar chart with gaps.

Try three 2.4 Variation and Evolution exam-style questions