A challenge in human genetics is to recognize genotypes without recourse to the deliberate cross and the F2 generation (The second filial generation, produced by self-crossing the F1). For this reason the study of human genetics relies so heavily on pedigree analysis. Phenotypic data is collected from several generations and charted. Many MCATs have included pedigree analysis in one form or the other over the years. The prototypical question is whether the trait is dominant or recessive. Here are some rules to follow. Remember that if a trait is dominent: 1) affected individuals have at least one affected parent. 2) the phenotype appears every generation and 3) two unaffected parents only have unaffected offspring (having the opposite occur way off in the corner of the chart is an old test-writer trick). Also, while a dominant allele tends not to skip generations, it can skip if masked by some other allele or process, so be sure to read the passage carefully.