back cross

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back cross A mating between individuals of the parental generation (P) and the first generation of offspring (F1) in order to identify hidden recessive alleles. If an organism displays a dominant characteristic, it may possess two dominant alleles (i.e. it is homozygous) or a dominant and a recessive allele for that characteristic (i.e. it is heterozygous). To find out which is the case, the organism is crossed with one displaying the recessive characteristic. If all the offspring show the dominant characteristic then the organism is homozygous, but if half show the recessive characteristic, then the organism is heterozygous. See also test cross.