GCSE Biology: Inheritance & Evolution — Topic Revision Workbook

Inside GCSE Biology: Inheritance & Evolution — Topic Revision Workbook

compare sexual and asexual reproduction and describe meiosis and the genome, master the genetic vocabulary and work through monohybrid crosses and their ratios, tackle inherited disorders and sex determination with probability questions, revise variation, natural selection, selective breeding, genetic engineering, extinction and classification, then plan and write a 6-mark answer. About 30 minutes.

Learning objectives

• reproduction and the genome — sexual versus asexual reproduction, meiosis and gametes, and DNA, genes, chromosomes and the whole genome;
• genetics and inheritance — the key terms (gamete, allele, dominant, recessive, homozygous, heterozygous, genotype, phenotype), Punnett squares and monohybrid cross ratios such as 3:1;
• inherited disorders and sex — dominant polydactyly, recessive cystic fibrosis, probability from crosses, and XX/XY sex determination;
• variation and evolution — variation and mutation, evolution by natural selection, selective breeding, genetic engineering, fossils, extinction and antibiotic-resistant bacteria, and classification;
• exam technique — planning and writing an extended 6-mark answer using correct scientific vocabulary.

Activities in this book

1. Task 1 — Reproduction, Meiosis & the Genome

   sexual reproduction mixes genes from two parents (via gametes and fertilisation) to give variation; asexual reproduction uses one parent and mitosis to make genetically identical clones. Gametes are formed by meiosis, which halves the chromosome number so the full number is restored at fertilisation.

2. Task 2 — Genetic Terms & Monohybrid Crosses

   a gene has different versions called alleles. Two identical alleles = homozygous; two different alleles = heterozygous. The alleles you carry are your genotype; the characteristic they produce is your phenotype. In a Bb × Bb cross the offspring are 1 BB : 2 Bb : 1 bb, giving a 3 dominant : 1 recessive phenotype ratio.

3. Task 3 — Inherited Disorders & Sex Determination

   polydactyly (extra fingers or toes) is caused by a dominant allele, so it can be inherited from just one affected parent. Cystic fibrosis is caused by a recessive allele, so a child must inherit two copies (one from each carrier parent). Sex is decided by the sex chromosomes: XX is female, XY is male.

4. Task 4 — Variation, Evolution & Classification

   variation comes from genes, the environment or both, and new alleles arise by mutation. Natural selection (Darwin) means the best-adapted survive and pass on their genes; selective breeding and genetic engineering are ways humans change species deliberately. Fossils and extinction are evidence of change over time, and living things are classified into groups.

5. Task 5 — Exam-Style 6-Marker

   a 6-mark question rewards a clear, logical explanation, not just facts. Plan three or four points, use correct terms (allele, dominant, recessive, gamete, natural selection) and link cause to effect. Aim for full sentences that a marker can follow step by step.

Suggestions for teaching

• Fix the vocabulary first. Learners cannot do crosses until gamete, allele, dominant, recessive, homozygous, heterozygous, genotype and phenotype are secure — drill these before Task 2.
• Model the Punnett square. Work a Bb × Bb cross on paper to show the 1:2:1 genotype ratio and the 3:1 phenotype ratio, then convert to fractions and percentages.
• Contrast the two disorders. Use polydactyly (dominant, one copy needed) against cystic fibrosis (recessive, two copies needed) so learners see why carriers matter.
• Tell the natural-selection story. Walk through antibiotic resistance step by step — variation, mutation, survival of the fittest, reproduction — as a model 6-mark answer.