Meiosis, Inheritance and Variation
Sources of genetic variation, Mendelian and non-Mendelian inheritance, linkage, sex linkage, pedigrees and probability.
How to study A-level Biology
Move between scales deliberately: identify the biological process, trace matter or information, use quantitative evidence, then evaluate the method and conclusion.
Core concepts
Concept 1
Mutation, crossing over, independent assortment and random fertilisation generate heritable variation.
Exam cue: Define symbols and parental genotypes before constructing a genetic diagram.
Concept 2
Alleles may show dominance, codominance, multiple-allele, sex-linked or linked inheritance patterns.
Exam cue: Use chromosome position to explain linkage, sex linkage and recombinant outcomes.
Concept 3
Genetic crosses and statistical tests connect a biological model with observed offspring data.
Exam cue: State the null hypothesis and degrees of freedom before interpreting chi-squared evidence.
Risk pitfalls and guardrails
Confusing homologous chromosomes with sister chromatids.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Using a phenotypic ratio without accounting for linkage or small samples.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Assuming a dominant allele is necessarily common or advantageous.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Memory anchors
Crossing Over
Non-sister chromatids of homologous chromosomes exchange DNA during meiosis I.
Independent Assortment
Homologous chromosome pairs orient independently at meiosis I.
Codominance
Both alleles contribute distinctly to a heterozygote's phenotype.
Linkage
Genes close together on one chromosome tend to be inherited together.
Test Cross
A cross with a homozygous recessive individual can reveal an unknown dominant phenotype's genotype.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
What is the main outcome of meiosis in a diploid organism?
What pairs at prophase I of meiosis?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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