Final answer:
The Punnett square is a tool used in genetics to predict that 75% of the offspring will display the dominant phenotype in a cross between two heterozygous individuals for a certain trait. It shows a 3:1 ratio, with 25% expected to express the recessive phenotype.
Step-by-step explanation:
The Punnett square predicted that 75% of the offspring would have a certain trait. This can be explained using the example of flower color in pea plants, where the phenotype purple is dominant over white. When two heterozygous purple flowers, represented as Bb, are crossed, the Punnett square facilitates the prediction of offspring characteristics.
In such a cross, the outcome will show a 3:1 ratio of the dominant to recessive phenotype. This means that approximately 75% of the offspring will display the purple phenotype, and 25% will have white flowers, as the recessive trait only appears when both alleles are recessive (bb).
A classic example of Punnett square predictions can be seen in Mendel's experiments with pea plants, where he observed similar ratios for traits like flower color. These concepts not only apply to monohybrid crosses but can also be extended to dihybrid crosses, as illustrated with the 9:3:3:1 ratio seen in cases considering two traits, such as seed texture and color in pea plants.