Mendelian Inheritance - Mendelian Inheritance Introduction...

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1 Mendelian Inheritance Introduction General information The concept of heredity predates the time of Mendel. The ancient Greek philosopher Hippocrates (around 400 B.C.E) proposed the concept of pangenesis. “Seeds” are produced by all parts of the body and are transmitted to the offspring. Greek theories persisted in some form for more than 2,000 years. Homunculus – a tiny, fully formed human that lived within the sperm cell. Spermists – sperm was responsible for the human characteristics of the offspring. Ovists – egg was responsible for human characteristics of the offspring. Work of Joseph Kölreuter (18 th century) supported the theory of blending inheritance. The idea that the factors that dictate heredity are blended together from one generation to the next. By the mid-19 th century it was believed that these blended traits could change over generations. Mendel’s Laws of Inheritance General information Mendel’s experimental approach to heredity began in 1856 and lasted only 8 years. He worked in a small (115-foot x 23-foot) plot. He kept detailed records that included quantitative data. His 1866 paper, “Experiments on Plant Hybrids,” was largely ignored by the scientific community, possibly because of the title and/or its publication in an obscure journal. Mendel’s work was independently rediscovered in 1900 by Hugh de Vries (Holland), Carl Correns (Germany), and Erich von Tschermak (Austria).
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2 Mendel chose pea plants as his experimental organism. Prior to Mendel, plant breeders had crossed (mated) distinct individuals to produce hybrids (the process is called hybridization). Mendel believed that the patterns of traits in these hybridization experiments were rooted in physical laws that could be explained by mathematical principles. Mendel chose the garden pea ( Pisum sativum ) as his experimental system (Figure 2.2). The species was available in several varieties with decisively different and easily recognizable characteristics. Pea plants can be easily crossed. Plant reproduction occurs by pollination (Figure 2.2c). Male gametes (sperm) are produced within pollen grains, which are formed within the stamen of the plant. Female gametes are produced within the ovules, which are formed within the ovaries of the plant. Pollen grains first land on the stigma. This is followed by the formation of a pollen tube, which delivers the sperm to the egg cell. With plants, self-fertilization (sperm and egg from the same individual) is possible. The structure of a pea plant favors self-fertilization because the stamens are covered by a protective petal (the keel). Cross-fertilization (Figure 2.3) involves the use of two parents. The large flowers of the pea plant make it possible to remove stamens from the flower, preventing self-fertilization and allowing selective breeding of plants to produce desired hybrids. Mendel studied seven traits that bred true.
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This note was uploaded on 05/19/2011 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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Mendelian Inheritance - Mendelian Inheritance Introduction...

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