Markup | Genome Research

Table 6.

Range of Nucleotide Frequencies (Percent) by Taxonomic Group and Codon Position

Taxon	A	C	G	T	G+C
	Combined 1^st and 2^ndpositions
Fishes	22–23	25–28	19–20	30–32	45–48
Coelacanth	25	27	18	30	45
Amphibians	24	25–28	18–19	30–33	46
Reptiles	24–25	26–27	17–18	31–32	43–45
Birds	23–24	29	17–18	30	46–47
Mammals	25–26	24–28	16–17	30–34	40–44
	3^rdpositions
Fishes	29–44	22–39	6–11	17–34	29–49
Coelacanth	48	28	7	17	35
Amphibians	36–43	22–35	5–12	17–30	27–47
Reptiles	37–46	29–33	5–11	19–20	36–43
Birds	38–41	35–43	6	14–18	41–48
Mammals	35–46	19–44	3–8	14–32	22–48