Question

The Lederberg replica plating experiment showed that

• A. mutations are actually pre-adaptive and evolution is not directed process, in fact evolution is based on chance events in nature and chance mutation in the organism
• B. mutations appear in organisms in response to change in the environment, conscious reaction, desire or use and disuse of organs
• C. mutations are random and continuous variations that form the raw material for gradual changes of evolution.
• D. all of these.

Answer 1

The correct option is D all of these.

Replica plating is a microbiological technique in which one or more secondary Petri plates containing different solid (agar-based) selective growth media (lacking nutrients or containing chemical growth inhibitors such as antibiotics) are inoculated with the same colonies of microorganisms from a primary plate (or master dish), reproducing the original spatial pattern of colonies. The technique involves pressing a velveteen-covered disk, and then imprinting secondary plates with cells in colonies removed from the original plate by the material. Generally, large numbers of colonies (roughly 30-300) are replica plated due to the difficulty in streaking each out individually onto a separate plate. The purpose of replica plating is to be able to compare the master plate and any secondary plates, typically to screen for a desired phenotype. Replica plating is especially useful for "negative selection". However, it is more correct to refer to "negative screening" instead of using the term 'selection'. For example, if one wanted to select colonies that were sensitive to ampicillin, the primary plate could be replica plated on a secondary Amp+ agar plate. The sensitive colonies on the secondary plate would die but the colonies could still be deduced from the primary plate since the two have the same spatial patterns from ampicillin resistant colonies. If one sees growth on the third (nonselective) plate but not the second one, the selective agent is responsible for the lack of growth. If the non-selective plate shows no growth, one cannot say whether viable cells were transferred at all, and no conclusions can be made about the presence or absence of growth on selective media. This is particularly useful if there are questions about the age or viability of the cells on the original plate.

So the correct option is 'all of these'.