Reduced efficacy of selection in regions of the Drosophila genome that lack crossing over

Table 1 Measures of codon usage bias, GC content, and gene length in the different recombination regions

	ENC	Fop	GC total	GC3	Length
High	47.41 (47.23-47.62)	0.545 (0.542-0.547)	0.548 (0.546-0.549)	0.669 (0.666-0.672)	1517 (1477-1562)
Intermediate	48.57 (48.33-48.83)	0.532 (0.528-0.535)	0.541 (0.538-0.543)	0.655 (0.651-0.659)	1476 (1424-1520)
Low	47.86 (47.44-48.25)	0.548 (0.543-0.554)	0.549 (0.546-0.552)	0.672 (0.664-0.679)	1489 (1422-1556)
No (N_O)	52.24 (49.69-54.42)	0.424 (0.378-0.467)	0.511 (0.466-0.547)	0.572 (0.495-0.638)	1238 (915-1590)
No (N₄)	54.14 (53.43-54.82)	0.263 (0.251-0.276)	0.422 (0.411-0.432)	0.368 (0.354-0.383)	2692 (2053-3532)
No (N_A)	53.70 (52.89-54.50)	0.300 (0.280-0.321)	0.432 (0.421-0.446)	0.393 (0.374-0.414)	2358 (1860-3016)

Values reported for ENC, Fop, GC total, and GC3 are means for all genes from D. melanogaster and D. yakuba combined (95% confidence interval). Values for gene length are the mean number of base pairs in D. melanogaster for all constitutively spliced exons concatenated, for each gene (95% confidence interval). The no crossing over region is divided as follows: N_O, non-fourth chromosome genes; N₄, fourth chromosome genes; and N_A, all no crossing over region genes. ENC, effective number of codons; Fop, frequency of optimal codons; GC3, GC content of the third position of codons.

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