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Particulate Inheritance: Mendel's Peas

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Particulate Inheritance: Mendel's Peas PARTICULATE INHERITANCE: MENDEL’S PEAS Darwin recognized the importance of individual variation in the reclusive monk made a great discovery: how traits are transmitted process of natural selection, but could not explain how individual from one generation to the next. differences were transmitted from one generation to another. In For each of the seven characteristics, he discovered that one 1866, only a few years after Darwin’s publication of On the Origin variety was dominant and one recessive. Though it didn’t show of Species, an obscure Austrian monk, Gregor Johann Mendel up in the first generation, the recessive trait did reappear in later (1822-1884), published a report of his breeding experiments on crosses, in statistically predictable proportions (1-11, 1-12). From the garden pea plant. This report described many features of the his controlled experiments and large samples of numerous mode of inheritance which Darwin was seeking. Unfortunately, breeding experiments, Mendel proposed the existence of Darwin did not read Mendel’s work, and Mendel’s great fundamental particles of inheritance. These, he noted, act as discoveries were not rediscovered by European scientists until distinct entities and do not blend during fertilization. Thus the 1900. offspring contain distinct particles from each parent. Mendel botanized in the quiet garden of his monastery in Bmo, focusing his attention on the common sweet pea, genus Choose two primary light colors to represent the parental Pisum. He meticulously recorded his observations and performed characteristics (a) and (b), and color the two test tube many experiments in order to confirm his results. Even by today’s drawings. Color the liquid in the receiving test tube with both rigorous standards, Mendel’s research is a model of the scientific parent colors. method. Mendel proposed that factors (or genes, as they are now Note the characteristics of Mendel’s plants. called) contributed by both parents were maintained in the Color gray the terms for the pea plant traits: seed shape, offspring in discrete units that could be inherited and passed on, seed interior, seed coat, and so forth. Using shades of two regardless of whether they were expressed in the outward contrasting colors, color the dominant and the recessive appearance of the offspring. This is the principle of particulate characteristics. inheritance. Mendel’s idea of inheritance challenged the popular 19th century notion of blending inheritance. Blending inheritance Mendel observed that his peas had seven easily observable maintained that traits passed on from the parents through sex cells characteristics that came in two, and only two, varieties. Seed are blended in the offspring, like mixing two colored liquids in a shape was either smooth or wrinlded; seed interior was either test tube. No blending occurred for any of the characters Mendel yellow or green; seed coat, gray or white; ripe pods, either inflated studied. or constricted; unripe pods, green or yellow; flowers positioned Mendel’s work remained almost unknown until 1900, when axially or terminally on the plant stem; and stems, long or short. three scientists working independently rediscovered Mendel’s When he crossed plants having smooth seeds with those having laws: Hugo de Vfies in Holland, Karl ~rich Correns in Germany, wrinkled seeds, the results were always smooth seeds, not slightly and Erich yon Tschermak in Austria. Modem views of inheritance wrinlded ones. date back to Mendel’s formulation of his laws of heredity. Mendel noted and carefully recorded the number of plants Since Mendel’s time, the science of genetics has exploded in in each generation.with a given trait. He believed that the ratio of complexity. Although he knew nothing of genes, chromosomes, plant varieties in a generation of offspring would yield clues about or DNA, his laws of heredity provided the backbone for the field inheritance, and he continually tested his ideas by performing of classical genetics and a basis for the modern molecular more experiments. From these patient studies, the modest approach to the study of evolution (Section 2). 1-10 R~,RTICULATE INHERITANCE; MENDEES PEAS "~Ien~ePs Peas" Article 1. Where was Gregor Mendel from and what was his occupation? 2. Which type of plant were his breeding experiments based on? 3. What was unique about the characteristics of this plant? 4. What great discovery did Mendel make? 5. This discovery led to Mendel’s principle of The principle challenged the popular belief that traits from the parents were.
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