 Incomplete dominance removed some of the ambiguities in using phenotypes to distinguish genotypes, but the combination of the four phenomena and linkage for multiple loci meant that Mendelian researchers had to distinguish among multiple hypotheses about the genotypes consistent with observed patterns of traits in the offspring of crosses. Background levels of mutation, including mutations in non-germ cells during the lifetime, ensure that even genotypes-as-classes consisting of clones or of identical or monozygotic twins are not made up of strictly identical members. Nevertheless, with suitable organisms and for certain traits, and under the inbreeding and control of conditions typical of Mendelian experiments, the painstaking work of inferring genotypes (as pairs of genes) from phenotypes could bear fruit.