Describe the experiment carried out by Hershey and Chase. Write the conclusion they arrived at.

OR

(a) Describe the observations made on the collection of white winged moths and dark winged moths in England between the years 1850 and 1920. What did these observations lead to?

(b) How is the use of herbicides, pesticides, and antibiotics by humans for various purposes, comparable with the observations made on moths in the above question? What is this type of phenomenon called?

Hershey Chase experiment
Bacteriophage release their genetic materials into their host. Bacteriophage are radio-labelled with ³²P and ³⁵S. Proteins will be labeled with ³⁵S and bacteriophage with ³²P has radioactive DNA. The viruses labeled with ³²P and ³⁵S are infected in E.coli hosts. After some time it is seen that the progeny contains ³²P radioactivity whereas no radioactivity is found in ³⁵S. This proves that DNA is the genetic material.

OR

a) Lichens are natural indicators of pollution. Barks of trees when associated with lichen becomes white in colour. Moths with melanin, i.e. dark winged moths became easy prey to predators, as they lost the advantage of camouflage. Due to industrialisation, the soot covered the tree trunks and lichens died. White winged moths were a prey to predators now. So, the number of melanic moths increased compared to white moths. This observation supports natural selection, a key aspect of Darwinism.

b) Excess use of herbicides, pesticides, etc., has only resulted in selection of resistant varieties in a much lesser time scale. This is also true for microbes against which we employ antibiotics or drugs against eukaryotic organisms/cell. Hence, resistant organisms/cells are appearing in a time scale of months or years and not centuries. These are examples of evolution by anthropogenic action. It is also understood that evolution is not a directed process in the sense of determinism. It is a stochastic process based on chance events in nature and chance mutation in the organisms.