Use of the chi-squared (χ²) test to compare the goodness of fit of observed phenotypic ratios with expected ratios
The chi-squared test is a statistical calculation. It tells you whether the difference between your actual breeding results and your predicted ratio is due to chance or something real.
Formula
χ² = Σ (O − E)² / E
Real World
Gregor Mendel's original pea-plant crosses produced ratios suspiciously close to 3:1 — modern statisticians have applied chi-squared tests to his data and debated whether his results were 'too good' to be entirely real.
Exam Focus
State the null hypothesis explicitly — 'there is no significant difference between observed and expected ratios' — as marks are reserved for it.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
How well did you know this?