Populations derived from crosses of elite genotypes are commonly used in plant breeding programs. Knowledge of the genetic variation among individuals and their progenies within F2 populations is essential for effective selection of important traits. The genetic variation and number of effective factors affecting the expression of quantitative traits within 30 F2 maize (Zea mays L.) populations were determined by different methods suggested for study of F2 populations. Estimates of heritability and number of effective factors varied among F2 populations for each trait, primarily because of the differences in trait expression between parents of crosses and the environmental effects upon individual plants. Average estimates of heritabilities for grain yield ranged from -0.03 to 0.63 among methods of estimation and ranged from 0.02 to 0.75 among methods of estimation for the same F2 population. The range of estimates of heritability and gene number among crosses and methods of estimation suggests that estimates are unique for a specific F2 population and for a specific method of estimation. If the newer techniques of marker-assisted selection are applied to F2 populations, the effectiveness of marker-assisted selection may vary among F2 populations
