The monk whose forgotten pea plants rewrote the laws of life
In the 1860s, Gregor Mendel’s experiments with pea plants were largely ignored by the scientific community. His radical idea—that heredity isn't a fluid blend of parents, but a precise exchange of discrete units—was only rediscovered decades later, eventually forming the mathematical foundation of modern genetics.
For much of the 19th century, biologists believed in 'blending inheritance,' where offspring traits were a smooth mixture of their parents. Mendel challenged this by studying discrete, binary characteristics in *Pisum sativum*, such as seed color and shape. Between 1856 and 1863, he meticulously tested approximately 28,000 pea plants, tracking generations from the parental (P) to the F3 generation. He discovered that traits like flower color do not blend; instead, they are passed down via 'factors'—now known as alleles—that remain distinct.
Mendel’s work established several fundamental principles. The law of segregation posits that allele pairs separate during the formation of gametes, ensuring each sperm or egg carries only one allele. The law of independent assortment suggests that genes for different traits are inherited independently of one another. He also identified the law of dominance, where a 'dominant' allele can mask the presence of a 'recessive' one. For example, crossing purebred purple and white flowers produces an F1 generation that is entirely purple, but the white trait reappears in the F2 generation in a predictable 3:1 ratio.
While Mendel's 'complete dominance' is the classic model, biology is more nuanced. Some traits exhibit 'incomplete dominance,' where the phenotype is an intermediate blend, such as the appearance of certain four o'clock plants. The full integration of Mendelism into modern science occurred much later. In 1915, Thomas Hunt Morgan linked Mendel's principles to the chromosome theory of inheritance, and by 1930, Ronald Fisher used these ideas to provide a mathematical basis for natural selection, creating the modern evolutionary synthesis.
Source: Mendelian inheritance
