Читать книгу The Handy Psychology Answer Book - Lisa J. Cohen - Страница 189

Darwin’s great contribution was to identify how nature acted on organisms to increase or decrease the likelihood of any given trait surviving into the next generation. But he also left many important questions unanswered. For example, how exactly are such traits passed from parent to offspring? The work of the monk and scientist Gregor Mendel (1822–1884) provided the foundation for the modern theory of genetics. Although his work was not well appreciated in his own day, by the twentieth century Mendel’s concepts were solidly integrated into modern biology. Mendel studied pea plants, which varied according to easily identifiable traits, such as height, pea shape, and flower color. By cross pollinating plants with various combinations of these traits and examining the proportion of offspring plants that displayed each trait, Mendel discovered two important principles which later became known as Mendelian Laws of Inheritance. Mendel posited that each parent carries two versions of some biological characteristic (what we now refer to as a gene) which determines a given trait. But each parent contributes only one version of this characteristic to the offspring. In this way, the offspring receives half of each parent’s genes.

These genes can be either recessive or dominant; dominant genes would always be expressed over recessive genes. For example, a single gene determines whether a pea plant will be short or tall. If an offspring receives two recessive genes, the offspring will express the recessive trait (the pea plant will be short). If the offspring receives two dominant genes, the dominant gene will be expressed (the pea plant will be tall). If the offspring receives one dominant and one recessive gene, the dominant gene will be expressed (and the plant will be tall).