59.4%GC3 content

52.9Effective codons (Nc)

250Coding sequences

8/26GC3 rank here

Scope: nuclear genes only

NCBI table 1 (Standard). Do not apply these frequencies to mitochondrial genes, where AGA, AGG, ATA and TGA carry different meanings. The four reassignments.

What distinguishes this table

The most constrained choice in Sheep is glutamine: of its 2 synonymous codons, CAG takes 75% of the family. Asparagine sits at the other end, spread almost evenly across its options (evenness 0.99 against 0.81 for glutamine). Those two families are where a codon-optimizer has the most and the least room to move.

Measured across all 59 sense codons, this table correlates most closely with Pig (r = 0.998) and least with Ferret (r = 0.808). A sequence tuned for the first would need little adjustment to move here; one tuned for the second would need a great deal.

Relative to the average across the 26 organisms on this site, Sheep leans hardest on CAC (+0.077 against the mean) and avoids CAT most (-0.077). Those two are the codons that most distinguish this table from the others.

Preferred and avoided codons

Amino acid	Preferred	Freq	RSCU	Avoided	Freq	RSCU
Alanine A	GCC	0.405	1.62	GCG	0.107	0.43
Arginine R	AGG	0.229	1.37	CGT	0.077	0.46
Asparagine N	AAC	0.561	1.12	AAT	0.439	0.88
Aspartate D	GAC	0.565	1.13	GAT	0.435	0.87
Cysteine C	TGC	0.582	1.16	TGT	0.418	0.84
Glutamate E	GAG	0.592	1.18	GAA	0.408	0.82
Glutamine Q	CAG	0.749	1.50	CAA	0.252	0.50
Glycine G	GGC	0.348	1.39	GGT	0.165	0.66
Histidine H	CAC	0.641	1.28	CAT	0.359	0.72
Isoleucine I	ATC	0.531	1.59	ATA	0.144	0.43
Leucine L	CTG	0.412	2.47	CTA	0.061	0.37
Lysine K	AAG	0.606	1.21	AAA	0.394	0.79
Phenylalanine F	TTC	0.566	1.13	TTT	0.434	0.87
Proline P	CCC	0.373	1.49	CCG	0.116	0.46
Serine S	AGC	0.247	1.48	TCG	0.062	0.37
Threonine T	ACC	0.376	1.50	ACG	0.129	0.51
Tyrosine Y	TAC	0.620	1.24	TAT	0.381	0.76
Valine V	GTG	0.472	1.89	GTA	0.094	0.38

Full codon usage table

Amino acid	Codon	Frequency	RSCU
Alanine A	GCC	0.4054	1.622
	GCT	0.2775	1.110
	GCA	0.2102	0.841
	GCG	0.1069	0.428
Arginine R	AGG	0.2287	1.372
	AGA	0.2028	1.217
	CGC	0.1987	1.192
	CGG	0.1843	1.106
	CGA	0.1084	0.650
	CGT	0.0770	0.462
Asparagine N	AAC	0.5608	1.122
Asparagine N	AAT	0.4392	0.878
Aspartate D	GAC	0.5646	1.129
Aspartate D	GAT	0.4354	0.871
Cysteine C	TGC	0.5816	1.163
Cysteine C	TGT	0.4184	0.837
Glutamate E	GAG	0.5922	1.184
Glutamate E	GAA	0.4078	0.816
Glutamine Q	CAG	0.7485	1.497
Glutamine Q	CAA	0.2515	0.503
Glycine G	GGC	0.3479	1.392
	GGA	0.2642	1.057
	GGG	0.2228	0.891
	GGT	0.1651	0.660
Histidine H	CAC	0.6407	1.281
Histidine H	CAT	0.3593	0.719
Isoleucine I	ATC	0.5309	1.593
	ATT	0.3250	0.975
	ATA	0.1441	0.432
Leucine L	CTG	0.4118	2.471
	CTC	0.2105	1.263
	TTG	0.1298	0.779
	CTT	0.1248	0.749
	TTA	0.0620	0.372
	CTA	0.0611	0.367
Lysine K	AAG	0.6056	1.211
Lysine K	AAA	0.3944	0.789
Methionine M	ATG	1.0000	1.000
Phenylalanine F	TTC	0.5656	1.131
Phenylalanine F	TTT	0.4344	0.869
Proline P	CCC	0.3728	1.491
	CCT	0.2692	1.077
	CCA	0.2424	0.970
	CCG	0.1157	0.463
Serine S	AGC	0.2466	1.480
	TCC	0.2184	1.310
	TCT	0.1906	1.144
	TCA	0.1413	0.848
	AGT	0.1413	0.848
	TCG	0.0619	0.371
Threonine T	ACC	0.3757	1.503
	ACA	0.2587	1.035
	ACT	0.2371	0.948
	ACG	0.1285	0.514
Tryptophan W	TGG	1.0000	1.000
Tyrosine Y	TAC	0.6195	1.239
Tyrosine Y	TAT	0.3805	0.761
Valine V	GTG	0.4718	1.887
	GTC	0.2526	1.010
	GTT	0.1815	0.726
	GTA	0.0941	0.376

Provenance

Computed from 250 RefSeq coding sequences for Ovis aries, sampled and counted codon by codon. Frequencies are relative within each amino acid family. Page generated 2026-08-09.

The full derivation of GC3, RSCU and the effective number of codons, along with the limits of each, is set out once in the methods note rather than repeated on every page.

Use this table

Nucleora codon-optimizes a coding sequence against this table directly, then folds the result and reports where structure would interfere with expression.

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