People have many types of traits -- blue eyes, brown hair, and freckles. The types of traits that a person can possess are called alleles.
Based on alleles that two parents have, it is possible to determine the probability that their offspring will inherit certain traits.
A monohybrid cross is a visual chart where alleles are converted into symbols that represent them called genotypes.
In this monohybrid cross, an uppercase "T" represents the allele for tongue rolling. A lowercase "t" represents the inability to roll the tongue.
When the alleles of two parents are combined, the probability that the offspring will be able to roll their tongue can be found. In this example, 2 out of 4 offspring will possess the allele for tongue rolling and will be able to roll their tongue.