**Core Concept**
Punnett's square is a graphical representation used in genetics to predict the probability of certain genotypes and phenotypes in offspring. It is a tool for predicting the possible genotypes and phenotypes of offspring from two parents, taking into account the alleles they carry for a particular gene.

**Why the Correct Answer is Right**
The Punnett square is essential in genetics for predicting the probability of dominant and recessive traits in offspring. It is constructed by drawing a square with the possible alleles of one parent on the top row and the possible alleles of the other parent on the side. The resulting combinations represent the possible genotypes and phenotypes of the offspring, allowing for the calculation of probabilities.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Punnett's square is not used for predicting the probability of diseases in a population.
**Option B:** This option is incorrect because the Hardy-Weinberg principle is used to predict the genetic structure of a population, not the probability of certain genotypes and phenotypes in offspring.
**Option C:** This option is incorrect because the pedigree chart is used to represent the inheritance of traits in a family, not to predict the probability of certain genotypes and phenotypes in offspring.

**Clinical Pearl / High-Yield Fact**
A memorable way to recall the purpose of Punnett's square is to think of it as a "genetic calculator" that helps predict the probability of certain traits in offspring.

**Correct Answer: C. Pedigree chart. Pedigree chart is used for predicting the probability of certain genotypes and phenotypes in offspring.