Experiment design 481
the effect of variety k. I n this context a variety is an mRNA sample. Since
Fisher’s pioneering work on ANOVA compared crop va rieties, the term variety
has remained in the terminology denoting different subspecies to be compared.
Besides the main factors a bove, the model in Eq. 15.8 also considers certain
factor interactions. The variety-gene interactions (V G)
kg
reflect differences in
expression for particular genes under the effect of a given variety. This is
the effect that we need in o rder to answer questio ns such as: “What are the
genes differentially r e gulated in condition A versus condition B?” The last
interaction term considered is the (AG)
ig
interaction. This term accounts for
the interaction between a rrays and genes. ...