Several other studies have also focussed on nucleotide asymmetries in DNA sequences to gain an insight into correlations, if any, in base composition and distribution. Arnold et al [4] used tetranucleotide frequencies in a third order Markov chain to predict the frequencies of longer oligonucleotides in the yeast genome and observed that the oligonucleotide frequencies depended strongly on base composition. Freeman [5] considered several prokaryotic DNA genomic sequences and found, from base composition asymmetries like purine excess over pyrimidines and coding strand excess, that the global minima of the purine excesses correlated with the origin of replication, and the maxima with the likely terminus for prokaryotic genomes and that such a prominent correlation between the purine excess and replication direction probably leads to excess pyrimidine accumulation in the sense strand and accordingly should increase the less mutationally vulnerable purine content of the coding strand. Prusak and Grzybowski [6] observed that there is a strong non-random distribution of nucleotides in the cytochrome b sequence in several species with the highest differences at the third codon position which is also the codon position of the strongest compositional bias; some species like quail, frog, python and elk appeared to prefer C over A in the light DNA strand whereas species belonging to the artiodactyls contained fewer pyrimidines compared to other species investigated.