Question

Give an account of Lederberg’s replica plating experiment to show the genetic basis of evolution.

Answer 1

Lederberg’s Replica Plating Experiment: Joshua Lederberg and Esther Lederberg, gave an experimental demonstration of a genetic basis of adaptation. They performed an experiment on bacteria to demonstrate the genetic basis of a particular adaptation. They obtained a ‘master plate’ of a bacterial culture by inoculating a dilute suspension of bacteria on an agar plate. After a certain period, the master plate was found to contain several bacterial colonies. Each colony represented a clone that has originated from a single bacterial cell as a result of repeated divisions. They prepared many replicas of the master plate on new agar plates. After that, they tried to grow bacteria on replica plates with an antibiotic (e.g., penicillin). Most colonies of the master plate failed to grow on replica plates having antibiotics. Only a few colonies that could be formed were found to be resistant to penicillin. It means that certain bacteria have acquired an ability to survive and grow in a new environment. This mutant strain of bacteria has adapted.

According to Darwinism, the original suspension of bacterial cells contained few mutant bacteria which had mutant genes that enabled them to survive the effect of penicillin and form colonies.

Lederberg's replica plating experiment

(Sensitive colony) (Resistant colony)
Fig. Lederberg’s replica plating experiment

The Lederberg’s replica plating experiment provided support to Darwinism is that the adaptation in bacterial cells arose due to the selection of pre-existing mutant forms of bacteria. It is based on the fact that the pattern of colonies seen in all the replica plates was the same.