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Short tandem repeats (STRs) are short sequences of DNA, usually 2 to 7 base pairs - AQA - A-Level Biology - Question 9 - 2023 - Paper 2
Question 9
Short tandem repeats (STRs) are short sequences of DNA, usually 2 to 7 base pairs. STRs are repeated a number of times, one after another. For example, the STR D5581... show full transcript
Worked Solution & Example Answer:Short tandem repeats (STRs) are short sequences of DNA, usually 2 to 7 base pairs - AQA - A-Level Biology - Question 9 - 2023 - Paper 2
Step 1
Describe how STRs could be removed from a sample of DNA.
Answer
To remove STRs from a sample of DNA, restriction endonucleases (enzymes) can be employed. These enzymes cut DNA at specific base sequences or pairs, effectively cleaving the DNA where STRs are located. By selecting appropriate restriction sites, scientists can selectively isolate or remove the STR regions.
Step 2
Explain the importance of knowing these base sequences in PCR.
Answer
Knowing the base sequences adjacent to the STRs is crucial for the polymerase chain reaction (PCR) because:
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Primers: The sequences are used to design primers, which are short strands of nucleotides that initiate DNA synthesis by providing a complementary base sequence for the DNA polymerase during the reaction.
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Specificity: Without the knowledge of these sequences, the amplification process might be non-specific, potentially leading to undesired products. Accurate priming ensures that only the target STR is amplified, optimizing the efficiency and accuracy of genetic analysis.