From: Codon usage is associated with the evolutionary age of genes in metazoan genomes
 | Age group* | # Genes | Coding region GC content | Protein length | ||
---|---|---|---|---|---|---|
 |  |  | Mean | SD | Mean | SD |
 | 1 | 612 | 0.54 | ± 0.10 | 363 | ± 466 |
 | 2 | 97 | 0.53 | ± 0.11 | 441 | ± 352 |
 | 3 | 1202 | 0.54 | ± 0.10 | 518 | ± 504 |
 | 4 | 581 | 0.55 | ± 0.09 | 531 | ± 472 |
Human | 5 | 648 | 0.52 | ± 0.09 | 477 | ± 424 |
 | 6 | 592 | 0.51 | ± 0.09 | 681 | ± 686 |
 | 7 | 605 | 0.53 | ± 0.10 | 571 | ± 400 |
 | 8 | 3914 | 0.54 | ± 0.09 | 557 | ± 498 |
 | 9 | 9023 | 0.53 | ± 0.09 | 525 | ± 399 |
 | Total | 17274 |  |  |  |  |
 | 1 | 983 | 0.49 | ± 0.10 | 384 | ± 391 |
 | 2 | 39 | 0.51 | ± 0.07 | 590 | ± 446 |
 | 3 | 861 | 0.51 | ± 0.07 | 534 | ± 516 |
 | 4 | 854 | 0.50 | ± 0.08 | 464 | ± 428 |
Mouse | 5 | 908 | 0.48 | ± 0.07 | 414 | ± 362 |
 | 6 | 708 | 0.50 | ± 0.07 | 623 | ± 659 |
 | 7 | 645 | 0.52 | ± 0.07 | 555 | ± 409 |
 | 8 | 4119 | 0.54 | ± 0.07 | 546 | ± 458 |
 | 9 | 9099 | 0.53 | ± 0.06 | 526 | ± 396 |
 | Total | 18216 |  |  |  |  |