Homologous Recombination in Maize

We have divided this chapter into two major sections: somatic and meiotic recombination. Somatic recombination in plants has been mostly monitored with artificial recombination substrates in transgenic systems. Although, in this area, maize has lagged behind other plants that can be more easily transformed, excellent progress has been achieved recently, as detailed in the first section. Specific topics discussed in this section are site-specific and targeted recombination. Research on meiotic recombination, particularly intragenic recombination, has been historically strong in maize relative to other plants, principally because the maize endosperm provides distinct advantages as an experimental unit of observation for recombination studies. It is, at the same time, large enough so that many traits can be scored and small enough so that many kernels can be screened. Many of the genes utilized in meiotic recombi-national analyses affect anthocyanin pigmentation in the aleurone layer of the endosperm, as will be evident in the second section. In this section we discuss the distribution of recombination junctions at the genomic, regional, and genic levels, as well as modifiers that affect that distribution. We consider the special case of tandem duplications and gene families as recombination substrates and discuss how recombination has been used as a tool in the genetic analysis of paramutation and disease resistance.