ACT Science Practice Question #1270 (Medium (32)) | Test Citadel
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ACT Science Difficulty: Medium (32)

Digital ACT Science Practice Question #1270

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In a forensic DNA investigation, a molecular geneticist conducts Polymerase Chain Reaction (PCR) amplification on a short tandem repeat (STR) locus. The sample initially contains exactly $20$ copies of the double-stranded template sequence. Assuming $100\%$ theoretical amplification efficiency, the number of double-stranded DNA copies after $n$ complete thermal cycles is given by $N = N_0 \times 2^n$. How many total double-stranded copies are present after $15$ complete cycles?
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Recall that $2^{10} = 1,024$. For $15$ cycles: $2^{15} = 32768$. Multiply by initial $20 \implies 655,360$.

Masterclass Solution & Distractor Trap Analysis

Using the PCR exponential amplification equation $N = N_0 \times 2^n$: Substitute $N_0 = 20$ and $n = 15$: $$N = 20 \times 2^{15} = 20 \times 32768 = 655,360.$$ Each thermal cycle doubles the template quantity....

Distractor Analysis: Trap choice eliminates careless test-takers who confuse roots with coordinates...

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