Appendix Probability and Hypothesis Testing in Biology Estimating Probability

In crossing his pea plants, Mendel obtained genetic ratios that were in excellent agreement with his model of factor segregation. Other workers soon obtained comparable results. The favorable agreement of data with theory reflected a basic property of Mendel’s model: if Mendelian factors are considered independent, then the probability of observing any one factor segregating among progeny must simply reflect its “frequency,” the proportion with which it occurs among the gametes. Frequencies are probabilities seen in the flesh. Mendel clearly understood this, and it was for this reason he sought large sample sizes. If you are flipping a coin, and you know the probability of “heads” to be 1/2, the way to get your observed frequency of “heads” to approximate the expected value most reliably is to flip the coin many times.