The chi-square test

You will write a small chi-square test for the results of a genetic cross.

The idea. The expected counts come from the ratio. Chi-square adds $(O - E)^2 / E$ over the classes. The ratio fits if the value is below the critical value.

Your tasks.

1. Finish expected_counts. It gives the list of expected counts for a total and a ratio such as [3, 1].
2. Finish chi_square. It gives the value for lists of observed and expected counts.
3. Finish fits. It says whether observed counts fit a ratio, when the critical value is critical.