The “Father of Genetics,” Gregor Mendel (1822–1884), is responsible for our understanding of hereditary traits such as green eyes and brown hair. By crossbreeding plants that had different traits, he discovered the basic laws of genetics still observed today.

Mendel was a Czech priest and biology professor at the University of Vienna. Through his experiments with pea pod plants, he discovered guidelines about how hereditary traits pass from one generation to another. Mendel’s law of segregation states that the sex cells of a plant may contain two different traits, but not both of those traits—a plant can have white flowers or purple flowers, but not both. His law of independent assortment (later known as Mendel’s law of inheritance) states that characteristics are inherited independently of each other—some people with blond hair have blue eyes, but not all people with blond hair have blue eyes. He also ascertained that each inherited characteristic is determined by two hereditary factors (known today as alleles), one from each parent. These factors decide whether a trait is dominant or recessive—or, in other words, whether it will be expressed visibly.

Between 1856 and 1863, Mendel worked in an experimental garden, breeding different combinations of pea pod plants and carefully recording the outcomes. He worked with seven characteristics: plant height, pod shape and color, seed shape and color, and flower position and color. His results showed that when a yellow pea and a green pea were bred together, for example, their offspring plant was always yellow— but in the next generation, green peas appeared in a ratio of one to three. He determined that green was a recessive trait and yellow a dominant one, meaning that green plants could occur only when an offspring received a green trait from each parent, not from just one.

Mendel published his research in 1866, but it wasn’t until 1900, after his death, that his work was rediscovered and his findings built upon. William Bateson (1861– 1926), a British geneticist who followed up on Mendel’s previous work, coined the terms gene, genetics, and allele in the early 1900s. In the next several decades, thanks to Mendel’s early research, genes and chromosomes were better defined.

ADDITIONAL FACTS

  1. The rediscovery of Mendel’s work led to the descriptions of genotype (the set of genes an organism carries) and phenotype (an organism’s observable characteristics, influenced both by the genotype and by the environment).
  2. The terms homozygous and heterozygous were later coined to describe genes that, respectively, contained two of the same alleles (two yellow dominant traits or two green recessives, for example) or one of each (such as one green recessive and one yellow dominant).
  3. In the 1950s, Arthur Kornberg (1918–2007) and Severo Ochoa (1905–1993) described DNA, the molecule of which genes are made, and James Watson (1928–) and Francis Crick (1916–2004) showed that DNA’s structure was a double helix.
  4. Humans and chimpanzees share 98 percent of their genes.