Effect of Half‐Sib and S1 Recurrent Selection for Increased Grain Yield on Allozyme Polymorphisms in Maize1

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Abstract
Allozyme frequencies at nine enzyme loci were monitored over eight cycles of selection for grain yield with the half‐sib (HT) and S1 progeny methods in maize (Zea mays L.) population ‘Krug BSK.’ Allozyme frequencies generally weres table over cycles in the presence of repeated small population size and high ~10% selection intensity. The average amount of genetic polymorphism for the nine enzyme loci was not different from the original population after the eight cycles of HT and S1 recurrent selection. Simple linear regression suggested the possibility of directional selection for changing allozyme frequencies at locus Peroxidase 1 (Prx1) in HT selections and loci Alcohol dehydrogenase 1 (Adh1), Malate dehydrogenase 2 (Mdh2), Acid phosphatase 1 (Acp1), and Prxl in S1 selections. However, more precise chi‐square analyses indicated that directional selection alone could not account for the observed allozyme frequency changes for any of the enzyme loci studied. It is concluded that stabilizing selection or random genetic drift associated with restriction of population size when lines were chosen to advance to the next cycle, or perhaps these two factors combined with undetected (because of small populatlon size) super imposed directional selection, can account for the observed allozyme frequency changes in the BSK populations studied.
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