Mendelian Genetics and Monohybrid Crosses

Gregor Mendel, an Augustinian friar working with garden pea plants in the 1860s, established the foundational rules of heredity long before anyone understood DNA. By tracking single characteristics across thousands of plants, he showed that inheritance follows predictable, mathematical patterns. These patterns remain the starting point for all modern genetics.

Alleles and the Concept of Genes

A gene is a length of DNA that codes for a specific polypeptide or influences a particular characteristic. Most genes exist in alternative versions called alleles, which differ by small changes in their base sequence. For a gene controlling seed color in peas, one allele might produce yellow seeds and another green seeds.

Because diploid organisms carry two copies of every autosomal chromosome, they p