A further round of selfing yielded four ears, two without and two with twins (frequency: 2.5% and 5.7% respectively), and, occasionally, seedlings with a stem divided into two stems after the first node while the primary root remains undivided (Fig. 1B). When twin plants are outcrossed as male parents to a different line, no twins are recovered in the F1.
In the selfed progeny of a twin plant reproduced in the greenhouse, seeds with twin embryos (Fig. 1C) are recovered with a high frequency (20%) while seedlings obtained by germinating normal seeds exhibit abnormal leaves with two lobes and a stunted growth. Their karyotype shows a normal chromosome number excluding a chromosomal unbalance as the basis of this trait. Taken as a whole these preliminary observations seem to indicate that the twin character is due to a monogenic recessive mutant with low penetrance upsetting the genetic program subtending apical meristem organisation.
Since the character appeared in the presence of Ac, we will assay if its origin is related to Ac induced transpositional mutagenesis.
1. A) twin plant. B) twin seedlings. C) twin seeds
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