Relationship between asymmetrical and symmetrical hybrid DNA formation during meiotic recombination.

The cross b2-17-A4 x b2(+) involving 2 mutant sites located one at each end of the b2 locus in Ascobolus immersus was analysed in order to look for aberrant segregations at one site among asci with aberrant 4:4 segregation at the other site. Most double site conversion asci with an aberrant 4:4 at one site showed a 5:3 segregation at the other site. Almost always, the aberrant 4:4 involved the low conversion end site and the 5:3 involved the high conversion end site. It is concluded that, in each individual meiosis, symmetrical hybrid DNA is often, if not always, physically associated with asymmetrical hybrid DNA. The asymmetrical hybrid DNA portion lies near the high conversion end and the symmetrical hybrid DNA portion near the low one.