Frequency of the transposable elementUqin Iowa stiff stalk synthetic maize populations

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Abstract
Summary: TheUqtransposable element is one of two transposable elements consistently found in maize (Zea maysL.) populations. Populations developed from two independent recurrent selection programs initiated in the Iowa Stiff Stalk Synthetic (BSSS) maize population were tested for the frequency ofUqtransposable elements to determine howUqfrequency has changed with cycles of recurrent selection. In the first programme, 13 cycles of half-sib and S2progeny recurrent selection [BSSS(S)C13] have been completed and 10 of the 13 cycles were assayed for activeUqelements. In the second programme, 11 cycles of reciprocal recurrent selection [BSSS(R)C11] have been completed and five of the 11 cycles were assayed for activeUqelements. The frequency ofUqwas different for the two recurrent-selection programmes. The percentage of plants containing activeUqelements increased from 19% (BSSS) to 91% [BSSS(S)C13] at a linear rate after 13 cycles of half-sib and S2progeny recurrent selection, whereas the percentage of plants containing activeUqelements decreased from 19% (BSSS) to 0% [BSSS(R)C11] after 11 cycles of reciprocal recurrent selection, with extinction of theUqelement occurring between the fifth and sixth cycles of selection. Our data suggest that the increase in frequency ofUqwith half-sib and S2progeny recurrent selection was predominantly due to random genetic drift coupled with a selective advantage possibly associated with a region of the genome linked toUq. Neither replicative transposition or chromosome assortment and segregation can be invoked to explain the change in frequency ofUqin these populations. The extinction ofUqafter reciprocal recurrent selection was best explained by random genetic drift.