Concept 9: The segregation of genes allows geneticists to make predictions

Geneticists like to predict the future. Genes behave in predictable ways which makes it possible to predict outcomes from a given cross. The favorite tool of the geneticist in making predictions is the Punnett square. The diagram depicts the process of segregation. The single letters on the outside of the squares represent the genes in the gametes of the parent. The paired letters in the squares show how the gametes can randomly come together and form the zygote and thus the next generation. Phenotype and genotype ratios can be determined from the squares in the diagram (Fig. 13).

Figure 13. The inheritance of genes is predictable behavior and therefore, trait inheritance can be predicted in controlled crosses. (Image by P. Hain)