A-LevelBiologyInherited changeOct/Nov 2025Paper 4 Q19 Marks
Guinea pigs, Cavia porcellus, vary in the length and colour of their fur. Fig. 1.1 shows a guinea pig with short black fur. [Figure 1.1] Two genes that determine the length and colour of the fur occur at the A/a locus and the B/b locus. These two gene loci are on separate autosomal chromosomes. • The allele A results in short fur. • The allele a results in long fur. • A is dominant to a. • The allele B results in black fur. • The allele b results in chocolate fur. • B is dominant to b.
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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