Genetic and Cytological Effects of Three Desynaptic Genes in the Tomato

In the normal tomato the genetic distance between d and aw is 12, between aw-wv 16, and between wv-centromere 38. In plants homozygous for the desynaptic gene as 1 , the percentage recombinants among the offspring is near normal. In as 4 plants the distance d-aw is 31 and aw-wv 39, a 2.4-fold increase for both map segments. In as b the distance d-aw is 18, the distance aw-wv is 36 and the distance wv centromere is 50.Cytology of the desynaptics indicates that initial pachytene pairing is normal, as judged from light and electron microscope observations. At later stages of pachytene, pairing is variable and at diakinesis there is a high frequency of univalents and a low frequency of chiasmata. The meiotic divisions are defective and fertility is low. Gametes from cells with high levels of crossing over may have a selective advantage in the desynaptic plants, so that as a result the frequency of recombinants is high among the progeny. However, in the case of as 4 and as b , it would seem more likely that the process of genetic exchange itself is interfered with.