Table 1.

Heterospecific autosomes and pachytene asynapsis in F1 hybrid males of various genotypes

Genotype	Autosomal constitution	Chr X	Fertility	Pachytene block	Pachytene asynapsis
PWD × B6	All APWD/B6*	PWD	ST	Complete	Multiple; excess of Ch17 and Chr 19 univalents
B6 × PWD	All APWD/B6	B6	F/ST	Weak	Limited; excess of Chr 19 univalents
PWD × B6.PWD-Chr 19	Chr 19PWD/PWD All other APWD/B6	PWD	ST	Partially released	Multiple; Chr 19 univalents missing
B6.PWD-Chr X.1s × B6.PWD-Chr 17	Chr 17PWD/B6 All other AB6/B6	PWD†	ST	None	Limited; only Chr 17 univalents present
PWD × B6. PWD-Chr 17	Chr 17PWD/PWD All other APWD/B6	PWD	F	None	None

F, fertile; ST, sterile.

*All heterospecific autosomal pairs consist of one Mus m. musculus (PWD) copy and one of Mus m. domesticus (B6).

^†Chr X.1s shows a 4.5 MB extension of the distal end of the proximal PWD interval, compared with Chr X.1.