lecture 1

lecture 1 - BICD 100 Genetics Winter 2008 Andrew Chisholm...

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Unformatted text preview: BICD 100 Genetics Winter 2008 Andrew Chisholm Lecture 1 8/1/08 Introduction to Genetics and Inheritance Heredity before Mendel Study of “generation” but no conception of heredity per se. Greeks (but not Aristotle): pangenesis; leads to Darwin’s “gemmules” made by all cells, somehow influence gametes. Lamarck: animal’s use or disuse of a character leads to its increase or decrease: Inheritance of Acquired Characteristics. Weissmann’s distinction between germline and soma rules out Lamarckism but not until 1880s Mendel’s Context Interest in animal and plant breeding coupled with mathematical training in Vienna Gartner, Kolreuter: establish that plants can reproduce sexually. Hybrids between two forms sometimes resemble one parent. “Identity of reciprocal hybrids”. “More variation” in next generation, but never quantitatively investigated. Mendel’s Experimental Design 1. Use peas Pisum sativum; easily grown and allow controlled cross- and self-fertilization. 2. Many variants from decades of selective breeding. In first two years show variants are true breeding. Differences are discontinuous, e.g. round / wrinkled seeds, no intermediate forms. Focus on seven such differences. 3. Perform crosses on large scale, count all seeds or plants. Quantitative analysis. Mendel’s Results Cross two true breeding varieties e.g. round x wrinkled (P0, parental generation). F1 hybrids are round not wrinkled. Self F1 and in F2 observe ratio 3:1 of one trait to the other. e.g. 3:1 round: wrinkled. 1/3 of round are true breeding, other 2/3 segregate wrinkled in F3. All seven traits show identical patterns. Mendel’s Model Trait is under control of two factors (formative elements). Factors segregate randomly in gametes of F1 hybrid. In F1 hybrid, round is ‘dominant’ to wrinkled (recessive). ‘Mendel’s First Law’ of equal segregation. Monohybrid vs. dihybrid crosses. ‘Mendel’s second law’ of independent assortment. Equal segregation explained by behavior of chromosomes in meiosis, and described mathematically by laws of probability. Independent assortment applies to genes on different chromosomes. Rediscovery of Mendel: Correns, Bateson et al. in 1900. Generalization of Mendelian ratios to other plants, animals. Modern terminology (Bateson and Johannsen): allele, gene, genetics. Genotype and phenotype. Homozygote and heterozygote. Statistical tests: the chi-squared test (Karl Pearson). Fisher’s reanalysis of Mendel’s data. Lucien Cuenot: apparent deviation from Mendelian ratios in yellow mice. Castle and Little’s explanation. BICD 100 Genetics Winter 2008 Andrew Chisholm How genotype influences phenotype. Genes on chromosomes; genes are made of DNA. But how does DNA influence phenotype? References for Lecture 1 Cobb, M. 2006. Heredity before genetics: a history. Nat Rev Genet. 7: 953-8. Mendel Mendel, J.G. (1866). Versuche über Pflanzenhybriden. Verhandlungen des naturforschenden Vereines in Brünn, Bd. IV für das Jahr, 1865 Abhandlungen:3-47. Go to www.mendelweb.org for an online version of Mendel’s Versuche with commentary. Mendel’s critics and their critics Fairbanks and Rytting, 2001. MENDELIAN CONTROVERSIES: A BOTANICAL AND HISTORICAL REVIEW American Journal of Botany 88(5): 737–752. 2001. Hartl, D. and Fairbanks, D.J. 2007. Mud sticks: on the alleged falsification of Mendel’s data. Genetics 175: 975-979. Mendeliana www.mendel-museum.org Klein, J. 2000. Johann Mendel’s Field of Dreams. Genetics 156: 1-6. The Rediscovery Castle, W.E and Little, C.C. 1910. On a Modified Mendelian Ratio Among Yellow Mice. Science 32: 868-870. Fisher, R.A. 1936. Has Mendel’s work been rediscovered? Ann. Sci. 1.115-137. Molecular cloning of the genes used in Mendel’s experiments Bhattacharyya, M.K., et al. 1990. The wrinkled-seed character of pea described by Mendel is caused by a transposon-like insertion in a gene encoding starch-branching enzyme. Cell 60: 115-122. Lester DR, Ross JJ, Davies PJ, Reid JB. 1997. Mendel's stem length gene (Le) encodes a gibberellin 3 beta-hydroxylase. Plant Cell. 9:1435-43. Armstead, I., et al. 2007. Cross-species identification of Mendel's I locus. Science. 2007 Jan 5;315(5808):73. (The yellow/green seed locus). ...
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This note was uploaded on 05/31/2009 for the course BICD 100 taught by Professor Nehring during the Spring '08 term at UCSD.

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