Lect1 - Prior history To appreciate Mendels work, one must...

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1 Prior history To appreciate Mendels work, one must keep in mind the prevailing theories of inheritance Preformationism : the idea that gamete contains an intact organism, was first proposed in the late 1600s. Blending inheritance : essences of both sperm and egg mixed to form offspring intermediate between the parents. Mendel ignored development, focused solely on transmission of traits
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2 Darwin: Among individuals of any species, there are differences (variations) Evolution cannot occur unless there are differences among individuals Variation is important Variation must be inherited Mechanism of inheritance of variations is important for understanding evolution Mechanism of inheritance not understood Darwin and Heredity
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3 Pangenesis: (1860s) Whole organism reproduces itself Gemmules determine characteristics (traits) of organism Germ cells contain gemmules of all sort and these are transmitted to next generation. Fertilization- gemmules unite and produce new cells of the types from which they are produced Pangenesis
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4 Cytology: Organisms are composed of cells The most distinct structure in a cell is the nucleus. ALL CELLS have a nucleus Cells are formed by the division of pre-existing cells (Mitosis). Mitosis described nuclear and chromosome dynamics Sperm and Ovum are cells. This links cells to heredity! Fertilization in sea urchin showed that sperm and ovum fuse. This links parents to offspring Ploidy? Cytology
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5 Meiosis Meiosis described Chromosomal changes -Reductional division of chromosomes keeps number of chromosomes constant. Nuclei of embryo and parents are diploids, but nuclei of germ cells are haploid Similar phenomenon not seen in any other cellular organelle.
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6 Cytology’s contribution prior to Mendel Heredity is a consequence of genetic continuity of cells by division Germ cells are the vehicle of transmission from one generation to the next Nucleus is crucial. During division it resolves into long chromosomes that split lengthwise Fertilization involves union of sperm and eggs Fertilization involves union of nuclei Chromosomes do not lose their individuality. They are inherited intact. Germ cells contain half the number of chromosomes found in body cells. Diploid embryo descends from maternal/paternal fusion of haploid chromosome groups
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7 The origin of genetics: The study of genetics begins when Gregor Mendel, in 1865, addressed the question : "How are characters passed on from one generation to the next?”
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8 Model organisms The genomes of many  organisms have been sequenced.  www.genomenewsnetwork.org A model organism is a species that has been widely studied, usually because it is easy to maintain and breed in a lab and/or has particular experimental advantages. Remember: processes are conserved!!!!!
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Lect1 - Prior history To appreciate Mendels work, one must...

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