Which one of the following conditions correctly describes the manner of determining the sex ?

When two unrelated individuals or lines are crossed, the per romance of F1 hybrid is often superior to both parents. This phenomenon is called :

ABO blood grouping is controlled by gene I which has three alleles and show co-dominance. There are six genotypes. How many phenotypes in all are possible -

In antirrhinum two plants with pink flowers were hybridized. The F₁ plants produced red, pink and white flowers in the proportion of 1 red, 2 pink and 1 white. What could be the genotype of the two plants used for hybridization ? Red flower colour is determined by RR, and White by rr genes -