An Analysis of Factors Controlling Chiasmata in Maize

抄録

Chiasma frequency at diakinesis was studied in eight inbred lines and three single crosses. In each case, comparison was made among three groups of anthers, classified according to the relative frequencies of division stages as follows: Group 1 with about 1:1 diakinesis: early stages, Group 2 with PMC's mostly in diakinesis, and Group 3 with about 1:1 diakinesis: late stages.
In the inbreds chiasma frequency was highest in Group 1 anthers and lowest in Group 3 anthers. The reverse was true in the hybrids, as indicated by the average values. But considering the hybrids individually, one hybrid gave a picture similar to the inbreds and the remaining two showed the reverse trend.
Two kinds of internal factors with opposing effects appear to determine chiasma frequency at diakinesis. One is temporal and tends to reduce the number by terminalization. The other is spatial and is due to the interaction of neighbouring meiocytes. While the first appears to be predominant in the inbreds, the second appears to be more conspicuous in some hybrids, tending to increase the incidence of chiasmata.