Final answer:
Di-hybrid crosses examine the inheritance of two traits at the same time, such as pea color and pea shape, and use a 16-square Punnett grid to predict the outcomes. The first generation shows only dominant traits, but when these are self-crossed, a 9:3:3:1 phenotypic ratio appears in the second generation, demonstrating Mendel's law of independent assortment. The principles are applicable to human traits like blood type.
Step-by-step explanation:
Description of Di-Hybrid Crosses
Di-hybrid crosses examine the inheritance of two traits simultaneously. For example, if we consider pea plants that are differing in two traits, such as pea color and pea shape, we can cross a plant with dominant traits (say round yellow peas) with one that has recessive traits (wrinkled green peas). After the first-generation (F1) cross, all the offspring will display the dominant traits due to the principle of dominance. However, when these F1 offspring are self-crossed or crossed among themselves, the result in the second-generation (F2) shows a 9:3:3:1 ratio for the traits, in accordance with Mendel's law of independent assortment.
Punnett Squares for Monohybrid and Di-hybrid Crosses
A monohybrid cross involves one trait and can be depicted in a 4-square Punnett grid, while a di-hybrid cross involves two traits and requires a 16-square Punnett grid to show all possible allele combinations from the parent gametes. When dealing with di-hybrid crosses, we typically cross individuals with a genotype such as AaBb, representing two different genes with two alleles each, one dominant (A or B) and one recessive (a or b).
Application of Mendelian Inheritance in Humans
Mendelian inheritance principles, like those observed in pea plants, are also applicable to certain human traits, such as blood type and other Mendelian diseases. The transmission of these traits can be predicted using the same methods of Punnett squares and understanding of dominant, recessive, and codominant alleles.