Piebald rats and selection

Investigators present a controlled breeding study that tests whether Mendelian determiners remain unchanged during crosses by selecting for increased or decreased pigmentation in piebald coat patterns of laboratory rats. They describe methods for grading dorsal pigmentation, establish parallel plus and minus selection lines, perform return and hybrid crosses with different stocks, and tabulate multigenerational outcomes. Statistical summaries and plates illustrate shifts in pigment distribution and the response to selection. The results are analyzed with respect to the theory of pure gametes and genotype–phenotype distinctions, showing that extracted recessive patterns and selection responses complicate simple notions of gametic purity.