Let’s say I was tracking the number of fruit flies buzzing around the summer fruit salad outside on the picnic table that either red or white eyes.

I would *expect* by the laws of genetics that only 25% of the flies would be red-eyed, and 75% white eyed.

So I cultivate a few generations of fruit flies over a few weeks and count their eye color as I go.

After looking at 5,000 flies, I have 2 sets of numbers: what I expected for red & white eyes, and what I actually observed for red and white eyes.

Chi square is a number indicating how far off the actual observation is from what I ideally expected.