tion, because such totally homozygous genotypes do not exist in the original population. Each inbred line can be crossed to every other inbred line to produce heterozy-gotes that reconstitute the original population, and an arbitrary number of individuals from each cross can be produced. If inbred line 1 has the genetic consti-tution A / A ? B / B ? c / c ? d / d ? E / E . . . and inbred line 2 is a / a ? B / B ? C / C ? d / d ? e / e ..., then a cross between them will produce a large number of offspring, all of whom are identically A / a ? B / B ? C / c ? d / d ? E / e . . . and can be raised in different environments. Results of norm of reaction studies Very few norm of reaction studies have been carried out for quantitative characters found in natural populations, but many have been carried out for domesticated species such as corn, which can be self-pollinated, or strawber-ries, which can be clonally propagated. The outcomes of such studies resemble those given in Figure 20-7. No genotype consistently produces a phenotypic value above
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