Answer:
Three nucleotide
Explanation:
Three nucleotides are required to code for one amino acid. There are four types of nucleotides A, T, G, C which make DNA. So a doublet of nucleotide code which involves only two nucleotide would be insufficient to code for 20 amino acids because if 4 different nucleotide is taken two at a time then it can only produce 16 amino acid(4²=16).
But if we take three-nucleotide than the number reaches 64 which is more than sufficient to code for 20 different amino acids(4³= 64). Therefore 3 nucleotides are needed to code for an amino acid.
Adenine forms two hydrogen bonds with thymine in DNA while three hydrogen bonds are formed between guanine and cytosine.
Thymine and cytosine are pyrimidines because they have a single ring structure. Adenine and guanine are purines because they have a double ring structure.
Bird skeletons are very delicate, and therefore, difficult to be preserved. The bones of the birds are soft. The small animals are very prone to physicochemical as well as biological decay. This is why the fossil record of bird is incomplete and well-preserved fossils of birds are rare to find, except at a few unusual sites.
