Differentiate between incomplete dominance and co-dominance. Substantiate your answer with one example of each.

OR

(a) Write the contributions of the following scientists in deciphering the geneticcode.

Georce Gamow ;Har Gobind Khorana ; Marshall Nirenberg ; Severo Ochoa

(b) State the importance of a Genetic code in protein biosynthesis.

OR

(a) George Gamow was a physicist who argued that if all 20 amino acids have to be coded by 4 bases then the code should be a combination of 3 bases.

Har Gobind Khorana contributed in the development of a chemical method to synthesize the RNA molecules with defined combination of bases.

Marshall Nirenberg developed a cell-free system of protein synthesis which helped the code to be deciphered (decoded).

Severo Ochoa discovered an enzyme (polynucleotide phosphorylase). It was helpful in polymerizing the RNA with defined sequences in a template independent manner.

(b) Importance of a Genetic Code in protein biosynthesis:

•The codon is triplet i.e. a combination of three out of four bases. 4 bases when combined in a combination of 3, it gives 64 possible combinations. Out of these 64 combinations, 61 code for amino acids and rest 3 are stop codons.

•One codon codes for only one amino acid. Therefore, it is unambiguous and specific.

•Some amino acids are coded by more than one codon. Therefore it is degenerate.

•Codons are read without punctuations.

•AUG has dual functions. It codes for Methionine and also acts as initiator codon.

•The code is nearly universal i.e. 1 codon codes for the same amino acids in all the organisms.