The beginning of a coding DNA sequence is shown below. It is read in groups of three bases from the left.
Original sequence: AAA CCG GGT TTA
The fourth base from the left is deleted. The remaining bases close together and are still read in groups of three from the same starting point.
The table gives the relevant triplet codes. Each different letter represents a different amino acid.
| Triplet | Amino acid |
|---|---|
| AAA | P |
| CCG | Q |
| GGT | R |
| TTA | S |
| CGG | T |
| GTT | U |
Which option gives the first three amino acids after the deletion and the number of these positions that differ from the original sequence?
P–Q–R; no positions differ.
P–T–R; one position differs.
P–Q–U; one position differs.
P–T–U; two positions differ.
76 exam-style questions on AQA GCSE Biology 6.1 Reproduction, covering 6.1.1 Sexual and asexual reproduction, 6.1.2 Meiosis, 6.1.3 Advantages and disadvantages of sexual and asexual reproduction, 6.1.4 DNA and the genome, 6.1.5 DNA structure, 6.1.6 Genetic inheritance, 6.1.7 Inherited disorders, and 6.1.8 Sex determination. Each one has a worked solution and a mark scheme showing where the marks go.