In Morgan’s experiment, parental phenotypes in F2 were about
Morgan's experiment crossed heterozygous F1 females carrying coupling configuration of recessive black body b and vestigial vg alleles to homozygous recessive tester males for phenotypic scoring. Unlinked expectation predicts fifty percent parental and fifty percent recombinant phenotypes yet observed parental classes dominated around ninety-eight point seven percent while recombinants rare around one point three percent indicating tight linkage preventing separation. Excess of parental types demonstrated genes reside on same chromosome with infrequent crossover events foundational evidence for chromosomal inheritance and quantitative basis for distance estimation via test cross.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 5: Morgan's Parental Excess 98.7% Demonstration