, to determine the genotype of an organism showing a dominant phenotype (whose genotype is unknown, either homozygous dominant or heterozygous), it is crossed with the recessive parent (homozygous recessive). This specific type of cross is called a test cross . In this scenario, the plant with the dominant black seed color (BB or Bb) must be crossed with the white seed plant (bb). If the unknown is homozygous (BB), all offspring will be black. If it is heterozygous (Bb), the offspring will show a 1:1 ratio of black to white seeds .