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Demonstrates Mendelian genetics by looking at the R (Colour) and Su (Endosperm) alleles in a dihybrid test cross for Purple (RR) Yellow (rr) with Starchy (SuSu) Sweet (susu).
The test cross is one of the fundamental tools devised by Gregor Mendel. In its simplest form it is an experimental cross of an individual organism of dominant phenotype but unknown genotype to an organism with a homozygous recessive genotype (and phenotype).
The purpose of the testcross is to determine if the unknown genotype demonstrating dominant phenotypes are homozygous for the dominant alleles, or heterozygous.
P RRSuSu x rrsusu
F1 Test Cross: Unknown x rrsusu
F2 (offspring of the test cross) Phenotype: Purple Starchy, Purple Sweet, Yellow Starchy, Yellow Sweet in a 1:1:1:1 ratio
The testcross reveals the presence of the recessive alleles in the F1 genotype (RrSusu), demonstrating heterozygosity.