question_answer

Write a note on Darwinism. How artificial selection is used to produce new varieties of crops?

OR

(i) Who coined the term 'genetic code'? What does it mean?

One of the codons on mRNA is AUG Draw the structure of tRNA adapter molecule for this codon. Explain the uniqueness of this tRNA.

 

Answer:

Charles Robert Darwin gave the theory of evolution which is popularly called Darwinism. He went on a sea voyage for 5 years on his ship called H.M.S. Beagle around the world. After returning back he concluded that existing living forms show similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago. Many such life forms do not exist as new life forms arose at different periods of history of earth. There has been gradual evolution of life forms. Every population has developed variation in characteristics which enable them to survive better in natural conditions. Darwin used the word fitness which according to him refers to only reproductive fitness. Those who better fit in an environment leave more progeny than others. Therefore they will survive more and are selected by nature. He called it natural selection and called it a mechanism of evolution.

Some important aspects of Darwinism are - Struggle for existence, variations, natural selection or survival of the fittest, inheritance of useful variations and formation of new species.

Man has modified plants and animals to suit their requirements. The breeders have successfully produced cow milk with increased milk yield. Many crop plants like broccoli, cabbage, cauliflower have been produced through selective breeding. Thus by selection, the breeders have successfully produced improved varieties of plants. The selected plants are interbreed to produce new varieties by the process called artificial selection.

OR

(i) The term genetic code was coined by George Gamow. It means that a sequence of 3 successive bases specifies one amino acid in a polypeptide.

(ii) AUG is initiator codon which signals the start of translation. The tRNA which has anticodon UAC joins with this codon through hydrogen bonds. It carries the amino acid - methionine. At this stage the tRNA lies at the P site of the ribosome and the A site is vacant to let another charged tRNA to enter.