Year 10 Science · Unit 1 · Lesson 2
Challenge Worksheet
Learning Goals
Design a mini-experiment
A scientist wants to test: "Can we determine how closely related two organisms are by comparing their DNA base sequences?" Plan and explain the investigation below.
Background
The DNA base sequence of genes is inherited from common ancestors. Organisms that diverged from a common ancestor more recently tend to share more similar DNA sequences. Modern techniques allow scientists to read the exact base sequence of specific genes from different species and count the differences.
(a) Describe the method a scientist could use to compare the DNA of two organisms. Include: which gene(s) they might compare, how they would collect and read the DNA sequences, and how they would quantify similarity.
(b) If the results showed that Species A shares 98% of its DNA sequence with Species B, but only 72% with Species C, what would this indicate about their evolutionary relationships? Explain your reasoning using your knowledge of DNA structure.
(c) Identify one limitation of using DNA base sequence comparison alone to determine evolutionary relationships. How could a scientist address this limitation?
1. Humans and chimpanzees share approximately 98.7% of their DNA sequence. However, humans and chimpanzees are clearly different organisms. Using your knowledge of how DNA base sequences code for proteins, explain how a small difference in DNA can lead to significant differences in body structure and behaviour.
2. The Human Genome Project, completed in 2003, mapped all 3 billion base pairs of human DNA. Scientists discovered that only about 1.5% of the genome codes for proteins. Suggest two possible roles for the remaining non-coding DNA, and explain why this was a surprising finding.
Wrap Up
In one sentence, what was the main idea of this lesson?