For a DNA-based relationship test, what should scientists compare?

• Equal-length stretches with matching letters.
• Corresponding stretches with positions aligned.
• Nearby stretches with the same total length.

Corresponding DNA positions are A G T C A in Species A and A C T T A in Species B. How many positions differ?

DNA changes occur at exactly the same rate in every gene and lineage.

In a made-up group, an ancestor gained a striped tail and its descendants retained it. Why can this support grouping them?

• The descendants evolved stripes independently.
• The descendants acquired stripes from their habitat.
• The descendants inherited stripes from that ancestor.

In which group does the lesson identify horizontal gene transfer as common?

• Birds
• Crocodiles
• Bacteria

Horizontal gene transfer must happen between different species.

What does a molecular clock need to estimate when lineages split?

• DNA differences and a fixed rate for every gene.
• DNA change rates and dated calibration evidence.
• DNA differences and the order species were named.

A scientist describes a phylogenetic tree as a hypothesis. What does that mean?

• A list of species sorted by their visible features.
• A record of species ordered by their discovery dates.
• A testable account of how lineages share ancestors.

An extinct animal has no usable DNA. Which approach can still test its ancestry?

• Use its age alone to group it with fossils of the same age.
• Use its size alone to group it with similarly sized fossils.
• Use inherited skeletal traits to test possible relationships.

Under a comparable-rate model, equal-length inherited DNA stretches differ at 2 sites for A-B and 8 for A-C. Which pair is predicted to have the more recent shared ancestor?

• A-B, because fewer differences suggest less elapsed time.
• A-C, because more differences suggest less elapsed time.
• Both pairs, because the counts reflect different stretch lengths.