Predict cloning outcomes
Predict which cells will grow after a cloning experiment using competent cells, ligation, and antibiotic selection.
- Competent cells can take up a plasmid: You must know only competent cells take up plasmid DNA before predicting which cells get the gene.
- Antibiotic selection grows only resistant cells: Predicting which colonies appear depends on knowing the antibiotic kills cells without the resistance gene.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
To predict colonies, check three things in a row: are the cells competent, did they take up a closed plasmid (ligation worked), and does that plasmid carry the resistance gene for the antibiotic on the plate.
Competent cells are mixed with a ligation reaction, then spread on antibiotic media. The diagram lists three checkpoints a cell must pass. Which cells will grow into colonies?
Reviewed| Checkpoint | Needed to form a colony? |
|---|---|
| Cell is competent (takes up DNA) | yes |
| Took up a closed plasmid with the gene | yes |
| Survives the antibiotic | yes |
- A.Every cell on the plate, because the growth media feeds all of them well
- B.Cells that took up no plasmid at all during the mixing step
- C.Only competent cells that take up a closed resistance plasmid and live
- D.Only cells that are NOT competent, which the antibiotic cannot kill
Show the worked solution ▾
Answer: C. Only competent cells that take up a closed resistance plasmid and live
- Step 1: List the requirements: From the table, a colony needs all three: competent, took up a closed plasmid with the gene, and survives the antibiotic.
- Step 2: Apply the filter: Cells missing any one of the three are killed by the antibiotic or never got the gene, so they do not form colonies.
Why it's right: A colony forms only when a competent cell takes up a closed resistance plasmid and then survives the antibiotic: all three must be true.
- A: The antibiotic kills unprotected cells; it does not feed every cell.
- B: Cells with no plasmid have no resistance gene and are killed.
- D: Non-competent cells cannot take up the plasmid, so they have no resistance gene.
Aligned to BI 6.1: predicting transformed colonies · reading level ~grade 9
- A colony count on a transformation plate is really a count of cells that passed all three checkpoints: competent, took up the gene, and resisted the antibiotic.
Fill these in as you work through the lesson.
- Competent cells (cells able to take up DNA):
- Ligation (the closing of the plasmid by glue):
- Selection (the antibiotic filter on the plate):
- Colony (a visible patch from one successful cell):
A colony appears only when a cell takes up a plasmid whose ligation AND the plasmid carries the gene that survives .
- What must be true about a cell for it to take up a plasmid at all?
- If ligation failed, why might far fewer colonies appear?
- On antibiotic media, which cells get filtered out?
A team mixes competent cells with a ligation that mostly failed to close the plasmids, then plates on antibiotic. Predict whether they will see many colonies, few, or none, and explain your reasoning step by step.