The genotype of an organism showing the dominant trait can be determined by crossing it with an organism that is a homozygous recessive. This is known as a test cross. In Mendel's monohybrid inheritance one allele was dominant over the other. Many plants and animals are known in which the hybrid shows the effects of both alleles as neither allele is completely dominant over the other. Both alleles exert their effects so that the hybrid has a phenotype that is intermediate between that found in its parents. This is known as incomplete dominance or blending inheritance. For example, a cross between a four o'clock plant which is homozygous for red flowers and another plant homozygous for white flowers produces an F1 generation of plants with pink flowers. Self-pollination is the F1 hybrids produces an F2 generation of plants with red, pink and white flowers in the ratio 1:2:1. Co-dominance occurs in the short-horned cattle where a homozygous red bull when crossed with a homozygous white cow yields an F1 generation of "roan" offspring with coats consisting of a mixture of red and white hairs. In this case, both alleles (i.e. The allele for red and allele for white) express themselves equally in the hybrid.