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Biology · Paper 2 · Foundation + Higher · B6

Inherited disorders and screening

Key ideas1 of 3

Dominant: polydactyly

Polydactyly means having extra fingers or toes. In the GCSE single-gene model it is caused by a dominant allele, P. PP and Pp express the condition; pp does not. The cross shown is Pp × pp, giving an equal chance of each phenotype.

A Pp by pp cross gives Pp, pp, Pp and pp; P is the dominant allele for polydactyly.

Next: Sex chromosomes and inheritance →
Practice, downloads and sources

Daily 5 · Exam practice · Revision sheet ↓

Foundation + Higher · B6. Fourteen core lessons, followed by two labelled Higher Tier lessons.

AQA Combined Science Trilogy 8464 · 4.6.1.5. Original notes, questions and diagrams. Models are simplified; teaching data are illustrative.