AQA GCSE Biology 4.6.1 Reproduction Exam Questions

About AQA GCSE Biology 4.6.1 Reproduction

Reproduction opens the AQA Inheritance, variation and evolution topic, examined on Paper 2. It compares sexual and asexual reproduction, explains meiosis, and covers DNA, the genome and how characteristics are inherited using genetic diagrams. GCSE Biology students also study the advantages of each type of reproduction, the structure of DNA and (Higher tier) protein synthesis and mutations. Examiners frequently set Punnett square and family tree questions with probabilities, ask you to compare mitosis and meiosis, and ask for evaluation of embryo screening for disorders such as cystic fibrosis and polydactyly.

What you need to know

• 4.6.1.1 Sexual and asexual reproduction Sexual reproduction involves fusion of male and female gametes (sperm and egg, pollen and egg cells) formed by meiosis, producing variation. Asexual reproduction involves one parent, no fusion of gametes and only mitosis, producing genetically identical clones.
• 4.6.1.2 Meiosis Genetic information is copied, then the cell divides twice to form four gametes, each with a single set of chromosomes. All gametes are genetically different. At fertilisation the normal number of chromosomes is restored and the embryo develops by mitosis.
• 4.6.1.3 Advantages of each (Biology only) Sexual reproduction gives variation, which helps survival when the environment changes and allows selective breeding. Asexual reproduction needs only one parent and is faster and more energy efficient. Malaria parasites, many fungi and plants such as strawberries reproduce both ways.
• 4.6.1.4 DNA and the genome DNA is a polymer of two strands forming a double helix and is contained in chromosomes. A gene is a small section of DNA coding for a particular sequence of amino acids to make a protein. The genome is the entire genetic material of an organism; studying it helps find genes linked to disease and trace human migration.
• 4.6.1.5 DNA structure and protein synthesis (Biology only) DNA is made of nucleotides, each with a sugar, a phosphate group and one of four bases (A, C, G, T); A pairs with T, C with G. Higher tier: three bases code for one amino acid; mRNA carries the template to ribosomes, where carrier molecules bring amino acids. Mutations can change protein shape and activity.
• 4.6.1.6 Genetic inheritance Learn gamete, chromosome, gene, allele, dominant, recessive, homozygous, heterozygous, genotype and phenotype. Use Punnett squares to predict outcomes as ratios, fractions, percentages or probabilities.
• 4.6.1.7 and 4.6.1.8 Disorders and sex Polydactyly is caused by a dominant allele; cystic fibrosis by a recessive allele. Embryo screening raises economic, social and ethical issues. Humans have 23 pairs of chromosomes; females are XX and males XY.

Common mistakes in 4.6.1 Reproduction

• Saying meiosis produces two cells. Meiosis involves two divisions and produces four genetically different gametes.
• Confusing genes and alleles. A gene codes for a protein; alleles are different versions of the same gene.
• Reading a 3:1 ratio as 'three out of three'. A 3:1 ratio means a probability of 3 in 4 (0.75) for the dominant phenotype.
• Saying a carrier of cystic fibrosis has the disorder. A carrier is heterozygous and has no symptoms.
• Thinking each child's chance changes with previous children. Each fertilisation is independent, so the probability is the same every time.

Try three 4.6.1 Reproduction exam-style questions