Advanced Placement (AP) Biology Practice Exam

What is a monohybrid cross?

1. A cross involving one pair of contrasting traits

2. A cross involving two pairs of contrasting traits

3. A comparison of multiple traits across a family tree

4. A study of genetic recombination across linked genes

The correct answer is: A cross involving one pair of contrasting traits

A monohybrid cross specifically refers to the genetic crossing of two individuals that differ in one specific characteristic or trait. In a typical monohybrid cross, the parents possess contrasting traits for a single characteristic, such as flower color in pea plants (e.g., purple versus white). By focusing on just one trait, this provides clear insights into the inheritance patterns of that specific characteristic, demonstrating how alleles are passed from parent to offspring. This type of cross is fundamental in understanding Mendelian genetics, as it illustrates the principles of segregation and dominance. It allows for the prediction of phenotypic ratios in the offspring, typically resulting in a 3:1 ratio in the case of a simple dominant-recessive relationship. The result not only reinforces the idea of traits being inherited but also sets the groundwork for more complex genetic studies involving multiple traits.