3.1: Genes are the Basic Units of Inheritance
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The once prevalent (but now discredited) concept of blending inheritance proposed that some undefined essence, in its entirety, contained all of the heritable information for an individual. It was thought that mating combined the essences from each parent, much like the mixing of two colors of paint. Once blended together, the individual characteristics of the parents could not be separated again. However, Gregor Mendel (Fig 1.10) was one of the first to take a quantitative, scientific approach to the study of heredity.
He started with well-characterized strains, repeated his experiments many times, and kept careful records of his observations. Working with peas, Mendel showed that white-flowered plants could be produced by crossing two purple-flowered plants, but only if the purple-flowered plants themselves had at least one white-flowered parent (Fig 1.11). This was evidence that the genetic factor that produced white-flowers had not blended irreversibly with the factor for purple-flowers. Mendel’s observations disprove blending inheritance and favor an alternative concept, called particulate inheritance , in which heredity is the product of discrete factors that control independent traits.