These days, scientists know how you inherit characteristics from your parents. They were able to calculate probabilities of having a specific trait or getting a genetic disease according to the information they have from the parents and the family history. But how is this possible to understand how traits pass from one living being to its descendants? We need to go back in time to the 19th century and learn about a man named Gregor Mendel. Mendel was an Austrian monk and biologist who loved working with plants by breeding the pea plants he was growing in the monastery's garden. Through his experiments, he discovered the principles that govern heredity. One of the most classic examples of Mendel's work involved crossing a purebred yellow-seeded plant with a purebred green-seeded plant. The resulting offspring produced only yellow seeds. Mendel called the yellow color trait dominant because it was expressed in all the new seeds. He then allowed the new yellow-seeded hybrid plants to self-fertilize. In this second generation, he obtained both yellow and green seeds, indicating that the green trait had been hidden by the dominant yellow trait. He called this hidden trait the recessive trait. From these results, Mendel inferred that each trait depends on a pair of factors, one from the mother and the other from the father. Nowadays, we know that these factors are called alleles and represent different variations of a gene. Depending on which type of allele Mendel found in each seed, we can have what we call a homozygous pea, where both alleles are identical, or a heterozygous pea, where the two alleles are different. This combination of alleles is known as the genotype, and its resulting appearance, whether yellow or green, is called the phenotype. To clearly visualize how alleles are distributed among descendants, we can use...