In 2006, twin girls born in the U.K. made for a puzzling headline: they appeared to be of two different races. One girl, with fair skin and blond hair, appeared northern European, while her sister had dramatically darker skin and hair. Both of their parents had racially mixed ancestry, and the girls seemed to exhibit features belonging to neither parent. If the twins had been born a hundred years ago, something would have seemed amiss, even supernatural, but modern genetics provides an explanation. A child's skin color is determined by up to seven genes, and mixed-race parents supply genes for skin types of both races. The odds that two mothers' eggs -- one carrying only the genes for "white" features and one carrying only the genes for "black" features -- would be fertilized by two sperm that were exact genetic matches are a thousand to one, unlikely but not impossible.
Modern genetics began with Johann Mendel, a priest, a scientist, and perhaps most important, a lifelong gardener. Born in 1822 in what was then the Austrian Empire, he was sent as a young man to an Augustinian abbey to pursue his studies. There he took the name Gregor and taught natural sciences to high school students. Encouraged by his professors and his fellow monks, he began to experiment with garden pea plants in the monastery garden. Through careful pollination techniques and statistical analysis of some 29,000 pea plants, he developed the first clear analysis of heredity. He demonstrated that an organism's characteristics are controlled by hereditary factors, and that these factors occur in pairs. Mendel published the results of his work in 1866, but his study was criticized and virtually ignored. In 1900, 16 years after his death, scientists working independently in three countries reached similar conclusions -- and discovered that Mendel had beaten them by more than 30 years. His paper "Experiments in Plant Hybridization" is now considered a seminal work in the field. (The New York Times ‘Smarter by Sunday – 52 Weekends of Essential Knowledge for the Curious Mind’)