In a freshwater alga, gene A codes for enzyme P.
Cells without a mutation make enzyme P only when they are in the light. A mutation occurs in non-coding regulatory DNA close to gene A. The coding sequence of gene A is unchanged, but mutant cells make enzyme P in both light and darkness.
Which statement explains the mutant cells' pattern of enzyme production?
The non-coding DNA began coding for enzyme P whenever the cells were kept in darkness.
The alga needed enzyme P in darkness, so the mutation occurred to switch gene A on.
The mutation changed enzyme P's amino acid sequence, so the enzyme remained active in darkness.
The mutation allowed gene A to be transcribed in darkness, so mRNA was made in both conditions.
186 exam-style questions on OCR GCSE Biology 5.1 Inheritance, covering 5.1.1 The genome, 5.1.2 Environment and phenotype, 5.1.3 Variants and mutations, 5.1.4 How genetic variants influence phenotype, 5.1.5 Asexual and sexual reproduction, 5.1.6 Haploid and diploid, 5.1.7 Meiotic cell division, 5.1.8 Single gene inheritance, 5.1.9 Predicting single gene crosses, 5.1.10 Sex determination, 5.1.11 Multiple gene inheritance, and 5.1.12 Development of our understanding of genetics. Each one has a worked solution and a mark scheme showing where the marks go.