Non-random chromosomal distribution of Ac-like sequences in inbred maize

Abstract

Summary: We have searched for evidence of historical transpositions of Ac-like sequences in four standard maize lines using the recombinant-inbred mapping technique. Thirty restriction fragments were mapped using EcoR I, EcoR V, and Hind III. The four inbreds contained 24 fragments which mapped to independent sites within each line; the other 6 fragments probably represented multiple mappings of the same element. Possible allelism between lines reduced this number to a minimum of 15 different sites containing Ac-like elements. The distribution of these sequences does not fit the expected Poisson distribution; instead, an unusually large number of these elements were found on chromosome 4. The other sequences were scattered randomly throughout the genome. With few exceptions, each line had sequences in different locations; however, the overall distribution of Ac-like sequences was similar for all lines. The non-random distribution of Ac-like sequences suggests that they have undergone a limited number of transpositions in maize; the distribution is incompatible with either complete immobility or frequent transposition.