a-m(Au)871618W1, a-m(Au)871618W2 and a-m(Au)flow

--Peter A. Peterson

The a-m(Au) allele (a very dark heavily mutating background with large colorless areas) is one of the numerous alleles at the site of the original En insert at the A1 locus. Its position is similar to the a-m(papu) allele of the A1 gene, 22bp in from the 5' end of the second exon (Schwarz-Sommer et al., EMBO J. 6:287-294, 1987). From the cross a-m(Au) Sh x a sh2 two exceptional kernels (low-spotting) arose.

In confirmatory testcrosses, the following progeny types were observed.
 
   
Round
  Ear Pale Spotted Total
  #1 119 117 236
  #2 107 121 228

It is clear that this allele is a basic pale colored that responds to an independently segregating En. This is one of numerous such alleles and brings up several points.

One, the functional component of En was lost leaving a remnant responsive allele. Therefore, a transposon undergoes numerous events other than complete excision. Thus it responds to En by retaining the terminal inverted repeats.

Secondly, the allele includes an insert that does not impair gene functioning. Its position in the exon is such that it must be included in the full transcript and is unlike the a-m15719 allele which is positioned at the end of the 3' end of the second exon (Tacke et al., Maydica 31:83, 1986). Apparently, additional amino acids in the first third of the second exon do not interfere with the near wild-type gene expression of the a-m(Au)871618W1 allele, which provides additional support for diversity in protein products generated from transposon inserts at a gene.

a-m(Au)871618W2. This allele is similar (pale, without En) to W1, though it occurred as an independent event. A similar segregation pattern supports the control of this allele by an independently segregating En.

a-m(au)-flow. A series of progenies have been uncovered from the a-m(Au) allele that exhibit a flow behavior (spotting, very late confined to the gown and/or shoulder of the kernel but absent in the crown). This phenotypic expression is quite transient and cannot be assured of its heritability in succeeding generations. This phenotype with a single seed descent crossing program ranges from near completely colorless to every kernel on the ear showing this phenotype. Obviously, this full allele is still present because the typical a-m(Au) allele is uncovered at random times. Thus, the flow behavior is transient and is probably a consequence of an inhibitory methylation pattern.


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