Figure 5. The trans-acting effect of consubspecific PWD/PWD stretches increases the probability of full synapsis of PWD/B6 intersubspecific homologs in males of 2-chr cross and 4-chr cross experiments.

The expected rate of synapsed pachynemas was calculated for each mouse in 2-chr cross and 4-chr cross experiments by multiplication of observed synapsis rates (i.e. assuming independence) of FISH analyzed chromosomes (e.g. Chrs 15, 16, 18 and 19 in 4-chr cross) and the observed PB6F₁ synapsis rates of the remaining autosomes. Asynapsis rate was calculated as a complement to synapsis rate. The difference between expected and observed overall asynapsis is most pronounced in 4-chr cross males with the lowest expected overall asynapsis rate. Recovery of spermatogenesis signaled by the presence of sperm in the epididymis occurs when more than 40% of pachynemas are fully synapsed. SC is sperm count.

Figure 5—figure supplement 1. Asynapsis rate of individual nonrecombinant consomic PWD/B6 chromosomes modified in trans by the probability of synapsis of the remaining three consomic chromosomes in the 4-chr cross in individual males compared to PB6F₁ hybrids.

Asynapsis rate of a given chromosome is in negative correlation (r = −0.88,–0.45, –0.80,–0.67 for Chrs 15, 16, 18, 19, respectively) with the probability that all of the other three analyzed chromosomes are synapsed. The estimate of the slope in log-log regression is β_{3_chrs_syn}=–0.418 (95% CI = –0.272 to –0.534), overall p=0.0266.