If you transform a DNA library into E. coli, plate the bacteria, pick a colony, and use that colony to start a liquid culture, to how many clones of the library will that liquid culture correspond?

Question

BlackTom AI · Accepted Answer

A single colony is clonal: it most commonly originates from one transformed cell (one colony-forming unit, CFU) that divided many times on the plate, so a culture derived from that colony corresponds to one clone.

1) Relevant concepts:
- Colony-forming unit (CFU): a visible colony on an agar plate usually arises from one viable cell (or a clonal cluster) that replicates into a large population.
- Plasmid inheritance: each daughter cell inherits the same plasmid insert from the original transformed cell, so descendants are genetically identical for the library insert.
- Library complexity vs. colony pick: the whole library contains many different clones, but selecting a single colony isolates one of those clones.

2) Step-by-step reasoning:
- You transform E. coli with a DNA library: many different plasmid variants enter different cells.
- You plate the transformed cells so that individual transformants are spatially separated and form individual colonies.
- Each colony grows from (and is composed of) the progeny of the original transformant that landed in that spot.
- Picking one colony and inoculating liquid culture expands that colony’s progeny; those cells all carry the same plasmid insert sequence as the original transformant.

3) Intermediate “calculation”/logic:
- 1 transformed cell → grows into 1 colony → pick 1 colony → liquid culture derived from descendants of that single transformant = 1 clone.

4) Why the correct answer is correct:
Because the act of picking a single colony isolates the descendants of a single transformation event (one plasmid insert identity), the liquid culture corresponds to that single clone of the library.

5) Why other options are incorrect:
- “Thousands”: the whole plate may contain thousands of different clones, but one picked colony does not represent them.
- “0”: incorrect because the colony supplies cells and plasmids—so it represents at least one clone.
- “Impossible to say”: under normal aseptic plating/picking assumptions, it is determinate: one colony → one clone. (Only rare exceptions, e.g., mixed colony or contamination, would complicate this.)

Conclusion: The liquid culture corresponds to 1 clone, matching the provided answer.

If you transform a DNA library into E. coli, plate the bacteria, pick a colony, and use that colony to start a liquid culture, to how many clones of the library will that liquid culture correspond?单项选择题

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