Year 10 Science · Unit 1 · Lesson 8
Challenge Worksheet
Learning Goals
Find the mistake
A student wrote this answer
"DNA evidence is infallible, a DNA match means guilt beyond all doubt. Unlike eyewitness testimony, DNA cannot be wrong. If the police DNA database shows a match between crime scene evidence and a suspect, the case is closed and no further investigation is needed. DNA profiling reads the entire genome, so there is zero chance of a false match between two different people."
1. Identify two specific scientific errors or overstatements in the student's answer.
2. Rewrite the incorrect parts of the student's answer so they are scientifically accurate. Your rewrite should explain: (i) what DNA profiling actually analyses, and (ii) what a "match" actually means statistically.
3. Give one real-world scenario where DNA evidence could be misleading in a criminal investigation, and explain what legal standard courts use when evaluating DNA evidence.
1. In 2023 Australian police used DNA genealogy databases to identify a suspect in a 1984 cold case. This involves comparing the suspect's DNA with a database of family members' profiles to find a near-match, then narrowing down the family tree. Evaluate both the power and the ethical risks of using genealogy databases in criminal investigations.
2. Explain why completing the full course of antibiotics has nothing to do with DNA profiling, but has everything to do with the principle of variation in a population. (This is a crossover question, use ideas from Lesson 12 if you have studied it.)
Wrap Up
In one sentence, explain why DNA evidence is described as probabilistic rather than absolute proof of guilt.