Question

Five Mark Questions :
Give a genetic explanation for the following cross. When a tall pea plant with round seeds was crossed with a dwarf pea plant with wrinkled seeds,then all the individuals of $F_1$ population were tall with round seeds. However, selfing among $F_1$ population led to a 9:3:3:1 phenotypic ratio.

Answer 1

The genetic explanation of the cross:

If pea plants with two pairs of contrasting characteristics like tall/dwarf and round/wrinkled seeds are crossed the F1 progeny would have all tall plants with round seeds according to the periwinkle of dominance. This implies that tallness is dominant over dwarfness and round seed is dominant over wrinkled seeds. In F2 progeny, there would be some tall plants with round seeds and dwarf plants with wrinkled seeds. However, there would be some plants with recombination of characters such as tall plants with wrinkled seeds and dwarf plants with round seeds. This depicts that tall-dwarf and round/wrinkled traits are inherited independently of each other following law of independent assortment. which states that when two traits are taken in a cross the segregation of one trait is independent to the segregation of other characters.

Phenotypic ratio:9/16 Tall Round : 3/16 Tall Wrinkled : 3/16 Dwarf Round : 1/16 Dwarf wrinkled ( 9:3:3:1).