What can the principles of probability can be used for?
The principles of probability have a many uses. They are used in genetics, in statistics , in chemistry, and many other places.
In classical genetics probability is used to calculate the odds of obtaining a given outcome of a genetic cross.
Historically the hypothesis of classical genetics were based on probability predictions. Because the outcome of the crosses matched the predictions of the theory.
For example if you have two hydrids blue eyes and brown eyes.
Both parents will have brown eyes. The cross of the children predicts the 1/4 of the offspring will have blue eyes and 3/4 will have brown eyes. In a small population the outcome may not match the predictions. The larger the population the closer the outcome will be to predictions based on probability.