Advanced Placement (AP) Biology Practice Exam

What does a Punnet Square illustrate in genetics?

1. A chart that shows all possible combinations of alleles from a genetic cross

2. A method for measuring dominant traits in a population

3. A visual representation of phenotypes only

4. A comparison of heterozygous and homozygous traits

The correct answer is: A chart that shows all possible combinations of alleles from a genetic cross

A Punnett Square is indeed a diagram used in genetics to visualize all possible combinations of alleles from a genetic cross between two parents. It serves as a predictive tool for determining the potential genotypes of offspring based on the genetic makeup of the parents. Each square in the grid represents a possible combination of alleles that can result from the fertilization process. By filling in the squares with the alleles contributed by each parent, one can easily see the ratios of different genotypes that may occur in the offspring. This is particularly useful for predicting traits controlled by single genes, providing insight into inheritance patterns such as dominant and recessive traits. Other options, while they touch upon aspects of genetics, do not accurately describe what a Punnett Square specifically illustrates. The method for measuring dominant traits in a population is not the focus of a Punnett Square, as it is more concerned with offspring predictions rather than population measurements. Similarly, while phenotypes are important in genetics, the Punnett Square directly represents genotypes rather than solely phenotypic expression, and it doesn’t compare traits but simply shows possible genetic outcomes from the parental combinations.