= Genetic redundancy
<Genetic redundancy> occurs when overlapping functions of different <genes> allow one to compensate for loss of another under specified conditions. A normal-looking single <mutant> can therefore conceal an important contribution to a process.
For a toy model, let $a,b\in\{0,1\}$ indicate whether either of two sufficient functions is present. The output
$$
y=1-(1-a)(1-b)
$$
is $1$ for $(a,b)=(1,1),(1,0),(0,1)$ and $0$ only for $(0,0)$. This is a <Boolean disjunction> model of compensation, not a claim that all biological effects are binary.
The <SHATTERPROOF genes> give an experimental example. Individual <SHATTERPROOF1> or <SHATTERPROOF2> disruptions did not produce the novel opening defect detected in the double <mutant>, connecting overlapping regulatory functions to <fruit dehiscence>.<SHATTERPROOF MADS-box genes control seed dispersal in Arabidopsis by Sarah J. Liljegren and others>[Abstract; functional redundancy and double-mutant phenotype]{ref}
The conclusion is conditional on the measured <phenotype> and environment. Compensation for opening a <fruit> does not establish identical <gene expression>, identical <DNA> sequences or interchangeability in every tissue.
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