y f o r l i n k a g e between t h e fra(X) l o c u s and a f a c t o r I X DNA RFLP (Brown e t a l , 1985). When fra(X> families were predivided i n t o two classes, one c o n t a i n i n g t h o s e w i t h non-penetrant ( N P ) males and one with apparent f u l l penetrance ( P I , evidence of s i g n i f i c a n t h e t e r o g e n e i t y was present. W e have now extended t h i s a n a l y s i s by adding DNA l i n k a g e information on 2 a d d i t i o n a l probes, 52A and ST14, s t u d i e d i n 16 fra(X> kindreds. These d a t a were combined w i t h information on 16 published f r a ( X ) families. There were 7 NP families and 25 P families. W e confirmed our previous f i n d i n g s of a higher recombination f r a c t i o n between f a c t o r I X and f r a ( X > i n P families (0 = .32 with l o d of .67) compared t o as NP families (0 = .06 with l o d of 6.11) which was s i g n i f i c a n t a t p< .01.
I n comparing recombination f r a c t i o n s for t h e a d d i t i o n a l probes, more recombination between 52A and t h e o t h e r l o c i was c o n s i s t e n t l y seen i n P compared t o NP families which suggested t h a t t h e r e may be a higher rate of recombination proximal t o t h e fra(X) l o c u s i n P kindreds. A s t r i k i n g l y higher recombination f r a c t i o n between 52A and f a c t o r I X was p r e s e n t i n comparing a l l fra(X> families (. 18) t o normal families (.02) which was s i g n i f i c a n t a t p< .001.