... increase of the GC content. The slope of the curve denotes the vari-ation rate of the GC content. According to the z¢curve, each chromosome is composed of several GC-rich and AT-rich regions alternatively. ... studied. The component xn, yn and zndisplays the frequencies distributions of the purine ⁄ pyrimid-ine, amino ⁄ keto and weak H-bond ⁄ strong H-bond along the sequence, respectively.Calculation ... indicates adecrease of the GC content or an increase of the AT con-tent, otherwise, a drop in the curve, i.e. k¢ < 0 indicates anincrease of the GC content or a decrease of the AT content.AcknowledgementsWe...