Work out chi square for genetics instantly with clear inputs, formula shown and shareable results.
Computes the chi-square goodness-of-fit statistic against a Mendelian ratio and compares it with the 3.841 critical value at one degree of freedom.
Chi-square test
chi2 = sum of (observed - expected)^2 / expected; with two classes there is 1 degree of freedom and a 5% critical value of 3.841
The data depart from the expected ratio more than sampling error alone would explain, so the genetic model is questioned.
When any expected count falls below about 5, where an exact test should be used instead.