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Gregor Mendel Discovers The Principles of Inheritance Lone Peak High School Biology 2002-03 By Brad Shuler
Who was Gregor Mendel? • Born in 1822 • Studied science, mathematics and statistics • Entered an Austrian monastery to be a monk • Studied heredity in peas • Discovered the principles of heredity
Mendel’s Observations • He identified that pea plants have a variety of traits when observing the different characteristics of the plant. • He developed “pure” strains of plants. (i.e. tall, short, green pod, yellow pod, wrinkled, round, etc.) These are often called purebreds. • The purebred plants consistently produced offspring with the given trait. (i.e. tall always produced tall)
Mendel’s PeasThese are the seven characteristics, each having two contrasting traits, that Mendel identified.
Mendel’s Experiments • He experimentally crosses different strains of “pure” plants (parental generation) to develop hybrids (F1 generation). • He then crossed these hybrids (F1 gen.) and analyzed the results (F2 gen.)
Mendel’s Results • The hybrids (F1 gen.) only displayed one of the parental traits. (tall) • When crossing two hybrids, some of the resulting offspring (F2 gen.) displayed one of the parental traits and some displayed the other. (some tall some short) • These traits in the F2 generation consistently occurred in a 3 to 1 ratio. (3 tall: 1short)
Mendel’s Conlusions:The Principle of Segregation • Each plant has two “factors” (genes) for any given characteristic (length of stem, color of pod, shape of seed, etc.) • They receive these “factors” from their parents. • When a plant reproduces it only passes one of its two “factors” to its offspring. The “factors” are contained in the gametes, the egg or sperm.
Mendel’s Conlusions:The Principle of Dominance and Recessiveness • Factors for certain traits seem to mask or hide the others when both are present in hybrids (Tt=tall). • Factors that are that always displayed when present are called “dominant”. • Factors that are hidden or masked by the dominant are called “recessive”. • Recessive traits are only displayed in purebreds (i.e. short-tt, yellow pod-yy).