AQA GCSE Biology 4.6 Inheritance, variation and evolution: a complete overview of DNA, genetics and evolution

What module 4.6 actually demands

Inheritance, variation and evolution is the genetics and evolution core of AQA GCSE Biology. The examiners reward precise vocabulary (allele, genotype, phenotype), confident Punnett square work, and clear reasoning about natural selection. Some parts of genetic crosses and DNA structure are higher tier.

This guide walks through the module and ties together the matching dot-point pages, each with its own practice questions.

Reproduction and meiosis

Sexual reproduction joins gametes from two parents, producing variation; asexual reproduction uses one parent and makes identical clones. Gametes are made by meiosis, which halves the chromosome number and produces four genetically different cells. Sexual reproduction's variation aids survival; asexual reproduction is fast and needs one parent.

DNA and the genome

DNA is a polymer of two strands in a double helix, carried on chromosomes. A gene codes for a protein; the genome is all of an organism's genetic material. Understanding the human genome helps find disease genes, treat inherited disorders and trace human migration.

Genetic inheritance

Characteristics are controlled by alleles (dominant or recessive). Know homozygous, heterozygous, genotype and phenotype, and use Punnett squares to predict ratios (a Bb by Bb cross gives 3:1). Sex is set by XX (female) and XY (male). Inherited disorders include polydactyly (dominant) and cystic fibrosis (recessive).

Variation, evolution and classification

Variation is genetic, environmental or both, with new alleles from mutation. Evolution by natural selection makes advantageous alleles spread; evidence comes from fossils and antibiotic-resistant bacteria, and new species form by speciation. Humans change organisms by selective breeding (risking inbreeding) and genetic engineering (transferring genes). Classification runs from Linnaeus's kingdom-to-species hierarchy and binomial naming to Woese's three-domain system based on DNA evidence.

How module 4.6 is examined

• Calculations. Punnett squares and probability/ratio of offspring.
• Vocabulary. Defining allele, genotype, phenotype and the rest precisely.
• Explanation. Natural selection, antibiotic resistance and speciation.
• Evaluation. Selective breeding, genetic engineering and embryo screening ethics.

Check your knowledge

A mix of recall and calculation questions covering module 4.6. Attempt them under timed conditions, then check against the solutions.

1. State one advantage of sexual reproduction over asexual reproduction. (1 mark)
2. How many genetically different cells does meiosis produce from one cell? (1 mark)
3. Define a gene. (2 marks)
4. Two heterozygous parents (Bb) have a child. What is the chance the child is homozygous recessive? (2 marks)
5. State the sex chromosomes of a human male. (1 mark)
6. Explain how a population of bacteria becomes resistant to an antibiotic. (3 marks)
7. Give one risk of selective breeding. (1 mark)
8. Name the three domains in Woese's classification system. (3 marks)