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IB DP Biology- D1.1 DNA replication- IB Style Questions For HL Paper 2 -FA 2025

IBDP Biology HL Paper 2 -FA 2025- All Chapters

Question

The diagram illustrates the tandem repeat regions present on two chromosomes in a pair of parents and their children. On chromosome 5 (Chr 5), the repeated sequence is AGAT, and on chromosome 18 (Chr 18), the repeated sequence is AGAA. One of the children is adopted.

(a) Describe how tandem repeats are used in DNA profiling.

(b) Identify which child is adopted and justify your answer.

(c) Explain the role of a promoter region in DNA.

▶️ Answer/Explanation
Detailed solution

(a)
Tandem repeats are short, repeating DNA sequences found in non-coding regions. The number of repeats varies widely between individuals and is inherited. In DNA profiling, these repeat regions are amplified and separated by gel electrophoresis or similar techniques. Each person has a distinct pattern of repeat lengths, making them useful for identity testing, paternity analysis, and forensic matching.

(b)
Child 1 is the adopted child.
Reason: On chromosome 5, Child 1 has 12 repeats, a number that neither parent possesses. Because children inherit tandem repeat counts directly from their parents, this mismatch shows that Child 1 is not biologically related at this locus.

(c)
A promoter is a regulatory DNA sequence located upstream of a gene. It provides the binding site for RNA polymerase, enabling the start of transcription. Promoters also regulate when, where, and how strongly a gene is expressed, and help unwind the DNA so mRNA synthesis can begin.

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