Association of endosperm reduction with parental imprinting in maize.

Among 38 reciprocal translocations between the maize B chromosome and the proximal region of the long arm of chromosome 10 were six interchanges associated with reduced endosperm development. These six have breakpoints that are the most proximal of the set and constitute a graded series with those broken nearer the centromere which have the most abnormal phenotypes. The group of six defines three major regions that produce the endosperm effects. The remaining 32 translocations reduce kernel size very slightly, suggesting the presence of a fourth region distal to all break-points.-The affected class of kernels lacks a paternally derived representative of that segment of 10L translocated to the B centromeric element (B(10) chromosome; 10 10 B(10)). An accompanying class of kernel in which the paternal B(10) chromosome is duplicated in the endosperm (10 10 10(B) B(10) B(10)) is normal. Kernels of the same endosperm constitution synthesized by introducing both 10 and B(10) maternally, however, are defective, resembling 10 10 10(B). Maternal B(10)'s are therefore unable to compensate for the absence of a paternal B(10). Clearly expression of the 10L genes involved supports normal endosperm growth only following pollen transmission.