Evolution Question 47
47. Using imprints from a plate with complete medium and carrying bacterial colonies, you can select streptomycin resistant mutants and prove that such mutations do not originate as adaptation. These imprints need to be used
[2005]
(a) on plates with and without streptomycin
(b) on plates with minimal medium
(c) only on plates with streptomycin
(d) only on plates without streptomycin
Show Answer
Answer : c
Hints & Solution
(c) Adaptation is generally due to selection of pre-existing variations and not due to new mutations or variations. This tends to support Darwin’s theory of natural selection. The basis was proved by replica plating experiment of Joshua Lederberg and Esther Lederberg. A number of sterile agar plates having antibiotic streptomycin were prepared. Bacteria were inoculated on the penicilling plates from the master plate by sterile velvet plate. Most bacterial colonies did not form replicas and inoculum died. Moreover a few colonies survived showing that they were resistant to streptomycin.
