Question

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 genetic code. Georce Gamow ; Hargobind Khorana ; Marshall Nirenberg ; Severo Ochoa

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

Answer 1

Incomplete Dominance :

When a cross is made between a recessive and a dominant parent then sometimes the phenotype of F1 generation does not resemble either of the two parents and is between the two. This is called incomplete dominance.

The inheritance of flower colour in the dog flower is a good example of incomplete dominance which we can understand with the help of given cross-



Co-dominance :

When two parents are crossed and F1 generation resembles both parents, it is called co-dominance.

A good example of co-dominance is ABO blood group in human beings. A cross is made to understand co-dominance better.


All of the above offspring in generation will have AB blood group as both alleles A and B are co-dominant and express equally.

OR

(a) George Gamow : George Gamow coined the term genetic code and argued that since there are only 4 bases and if they have to code for 20 amino acids, the code should constitute a combination of bases. He suggested that in order to code for all the amino acids the genetic code should be made up of 3 nucleotides.

Hargobind Khorana : Hargobind Khorana developed chemical method that was instrumental in synthesising RNA molecules with defined combination of bases. Using synthetic DNA, he prepared polynucleotide with known repeating sequence, e.g., CUCUCUCUCUCU

Marshall Nirenberg : Nirenberg used a synthetic poly U RNA and deciphered the code by translating this as polyphenylalanine.

Severo Ochoa : Severo Ochoa discovered the enzyme named Severo Ochoa enzyme which is a polynucleotide phosphorylase. This enzyme is helpful in polymerising RNA with defined sequences in a template-independent manner.

(b) The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells. The genetic code is nearly universal language that encodes directions for cells. Their arrangement as codons, store the blueprint for amino acid chain. This chain in turn form proteins which comprise or regulate the biological processes in every living beings.