Final answer:
A monohybrid cross deals with one trait and a single pair of alleles, resulting in a 3:1 phenotypic ratio, whereas a dihybrid cross addresses two traits and two pairs of alleles, leading to a 9:3:3:1 phenotypic ratio, as shown in larger Punnett squares.
Step-by-step explanation:
The difference between a monohybrid cross and a dihybrid cross is primarily the number of traits being considered. A monohybrid cross involves organisms that are heterozygous for a single character, meaning here the cross focuses on one characteristic, such as seed color. On the other hand, a dihybrid cross involves organisms that are heterozygous for two characters, like seed color and seed shape. For instance, using Punnett squares to demonstrate a monohybrid cross, you would see a cross between parents with genotypes YY (yellow seeds) and yy (green seeds), predicting outcomes for one trait. All the resulting offspring from this cross would be Yy with yellow seeds due to yellow being the dominant allele. In contrast, the dihybrid cross involving two traits (such as AaBb for both seed color and seed shape), results in a 16-square Punnett square to determine the possible genotypes, leading to a 9:3:3:1 phenotypic ratio if both traits are independently assorting.
For example, in a dihybrid cross examining seed color (Y for yellow and y for green) and seed shape (R for round and r for wrinkled) with parents both with genotypes AaBb, the gametes could produce offspring with varying combinations of these traits, demonstrating the principle of independent assortment originally described by Mendel.