A-Level Biology: Inheritance, Populations and Evolution

Genetics and evolution at A-level combine cross-diagram fluency with population-level mathematics, and the exam rewards students who can move between the two. This quiz spans that whole range.

The inheritance questions cover the standard cross repertoire with concrete, fully stated scenarios: the 3:1 monohybrid ratio from a heterozygous self-cross, the 9:3:3:1 dihybrid ratio with independent assortment, codominance through the ABO system — tested on which genotype produces the AB phenotype — and the pre-zygotic versus post-zygotic sorting of isolation mechanisms.

The statistics layer is exam-realistic: a chi-squared interpretation question — calculated value exceeding the critical value at the 0.05 level means the difference is significant and the null hypothesis falls, the phrasing students routinely invert — and a full Hardy-Weinberg calculation from raw numbers (20 homozygous recessives in 500 individuals, q² = 0.04, q = 0.2), with the equilibrium's assumptions tested separately as a multi-select.

The evolution questions complete the set: selection types with disruptive selection tested by its both-extremes signature and speciation link, the founder effect identified from concrete scenarios, genetic drift, and the allopatric-sympatric distinction by the presence or absence of geographic separation.

Every cross states its alleles and every calculation gives its numbers in the question body. The explanations show working, not just answers — matching how this section's marks are actually awarded — and the set follows naturally from the Genes and Protein Synthesis quiz in this collection.

• Predict mono- and dihybrid ratios and handle codominance and multiple alleles
• Interpret chi-squared results against critical values correctly
• Perform Hardy-Weinberg allele-frequency calculations from raw counts
• Classify selection types and isolation mechanisms
• Distinguish allopatric from sympatric speciation and recognise drift and founder effects

Topic scope follows the genetics, populations and evolution content of the DfE A level biology subject content as delivered in current exam-board specifications: inheritance patterns, chi-squared, Hardy-Weinberg, selection and speciation.