= Model organism evidence transfer
Evidence transfers at a stated level. <Sequence alignment> can suggest a candidate relationship between <genes>; <functional complementation> tests whether a candidate can supply a particular function in a chosen recipient. Neither alone establishes identical native <gene expression>, identical <signal transduction>, or identical consequences in every <species>. The <yeast cross-species complementation experiment> is especially useful because it tests a conserved function by intervention rather than assuming it from resemblance. <Pathways over Time: Functional Genomics Research in an Introductory Laboratory Course by Todd D. Reeves and others>[Reeves et al. (2018), project design, pp. 3–4, and Course Activities, pp. 5–6]{ref}
\Image[/model-organism-evidence-transfer-boundaries.png]
{title=What a <model organism> experiment establishes, and what needs another test}
{description=Original evidence map using the <yeast cross-species complementation experiment>. Solid arrows indicate an experimental question that can be addressed in the recipient; dashed arrows mark additional claims requiring evidence. This is a schematic of inference boundaries, not a <phylogenetic tree>, a measured pathway, or a claim about medical outcomes.}
Even successful <functional complementation> occurs within a specific <genetic background>, nutrient supply and imposed <gene expression>. The <enzyme> may work with the recipient’s available <substrates> and partner <proteins> at an experimentally imposed abundance. Establishing the same role in the donor <species> calls for experiments there; establishing behavior under another condition calls for experiments under that condition. A conserved component can therefore coexist with context-dependent behavior of an entire pathway. This separation makes <model organisms> powerful: an accessible experiment supplies a precise mechanistic foothold and a better question for the next system.
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