Table 2.

Numbers of synonymous allele-specific switches from preferred to nonpreferred codons and from nonpreferred to preferred codons that have occurred on the Neurospora tetrasperma mat a and mat A chromosomes (relative to Neurospora crassa)

N tetrasperma chromosomea	Type of allele-specific switchb	Type of codon located in:			No. of switchesc	Excess of switches from PR to NPRd	FrExcess NPRe
		N. crassa	N. tetraspermamat a	N. tetraspermamat A
Pseudoautosomal regions
mat a	PR to NPR	PR	NPR	PR	0	−1	−0.04
	NPR to PR	NPR	PR	NPR	1
mat A	PR to NPR	PR	PR	NPR	2	+2	0.08
	NPR to PR	NPR	NPR	PR	0
Stratum 2
mat a	PR to NPR	PR	NPR	PR	9	+5	0.27
	NPR to PR	NPR	PR	NPR	4
mat A	PR to NPR	PR	PR	NPR	7	+4	0.22
	NPR to PR	NPR	NPR	PR	3
Stratum 1f
mat a	PR to NPR	PR	NPR	PR	232 A	+98	1.26
	NPR to PR	NPR	PR	NPR	134 B
mat A	PR to NPR	PR	PR	NPR	263 A	+135	1.73
	NPR to PR	NPR	NPR	PR	128 B

^aThe total numbers of codon positions examined for the pseudoautosomal region, stratum 2, and stratum 1 are 25,502, 18,419, and 77,910, respectively.

^bPR, preferred codons; NPR, nonpreferred codons.

^cWithin each stratum, values followed by different letters indicate a statistically significant difference (P < 0.05) between the number of switches from PR to NPR and the number of switches from NPR to PR.

^dData shown are based on total numbers of switches from PR to NPR and from NPR to PR where the amino acid is conserved. When all possible switches, regardless of amino acid status, are included, the net excess remains the same for the pseudoautosomal region; the values for stratum 2 are +5 for both the mat a and mat A chromosomes; and the values for stratum 1 are +100 for mat a and +138 for mat A.

^eFrequency of excess PR-to-NPR switches per 1,000 codon positions, calculated as (number of PR-to-NPR switches − number of NPR-to-PR switches)/total codon positions examined × 1,000.

^fThree codon positions in stratum 1 had a codon switch on both the mat a and mat A chromosomes and were excluded from these results.