A 20,000-guide library needs average coverage of 500 guide-bearing cells per guide at the stated stage. How many guide-bearing cells are required? Type the number.

Answer: ______________

Which plan describes a pooled single-guide CRISPR knockout screen?

• Mix guide-bearing cells and compare guide counts before and after selection.
• Keep each guide in a separate culture and call each culture the full pooled library.
• Apply selection before adding guides and infer guide effects without an initial sample.

You want genes whose knockout reduces growth or survival in this cell line. Which screen readout fits?

• Positive selection: seek guides enriched among drug-resistant survivors.
• Endpoint-only counting: call every rare guide essential without an initial sample.
• Negative selection: seek guides depleted relative to their initial counts.

In each of two independent repeat cultures, Gene X's four guides have fold enrichments 8, 1, 1, 1; Gene Y's have 3, 3, 3, 3. Non-targeting controls stay near 1. Which preliminary interpretation fits?

• Declare Gene X causal because its largest guide effect exceeds every Gene Y effect.
• Prioritize Gene Y for follow-up because its guides agree across both repeats.
• Reject both genes because targeting guides must always match non-targeting controls.

A drug kills susceptible control cells. You want perturbations that let cells survive this drug. Which selection design fits?

• Negative selection: prioritize guides depleted as their cells become less likely to survive.
• Positive selection: prioritize guides enriched among surviving cells.
• No comparison: call every surviving guide causal without baseline counts or controls.

What is the main use of non-targeting guides, designed without a genomic target, in this screen?

• Provide a reference for background variation in guide counts.
• Prove that every targeting guide cuts only its intended genomic site.
• Reproduce all DNA-cutting effects caused by guides targeting genes.

In a growth-depletion screen, confirmed active guides against genes required in this cell line remain near baseline. What is the best next step?

• Declare all genes dispensable because these controls stayed near baseline.
• Accept the hit list unchanged because these controls never need to deplete.
• Troubleshoot conditions and readout before interpreting the hit list.

An 8,000-guide library needs average coverage of 500 guide-bearing cells per guide after a loss step. Exactly 80% of starting guide-bearing cells remain, with guide proportions unchanged. How many guide-bearing cells must you start with?

Answer: ______________