How did Mendel figure out the law of independent assortment?

Answer 1

Mendel figured this out by following two characteristics at the same time. (dihyrid).

As opposed to the law of segregation where he only followed one. (monohybrid).

He crossed two true breeding varieties that differed in two characters.

The F1 generation of these were both heterozygous displaying the dominant phenotype.

By breeding these together there could have been two outcomes:

1: the predicted offspring of the F2 generation would have a phenotypic ratio of 3:1, like the monohybrids, (meaning the inheritance of the two characters were dependent upon each other); or

2: the predicted offspring of the F2 generation would have a phenotypic ratio of 9:3:3:1. Meaning the two characteristics were inherited independently.

As it turned out the second was true for all his experiments. The numbers didn't lie.

Consider the two traits in the following (Trait One: "Oo" and Trait Two "Tt"):

P Generation:

OOTT bred with oott

Gametes would be:

OT and ot.

F1 Generation:

Both OoTt

F2 Generation showing independent assortment:

OOTT OOTt OoTT OoTt

OOTt OOtt OoTt Oott

OoTT OoTt ooTT ooTt

OoTt Ottt ooTt oott

Note the phenotypic ratio: 9:3:3:1.

This outcome would have not been displayed if the traits weren't assorted independently.