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Gregor Johann Mendel • 1822- 1884 • Austrian monk • Experimented with pea plants • He thought that ‘heritable factors’ (genes) retained their individuality generation after generation Time Line • 1831 Charles Darwin joins crew of Beagle • 1839 Schleiden and Schwann propose the Cell Theory • 1847 Semmelweiss proposes that infection is spread by contaminated hands of physicians. • 1856 Mendel begins hybridization studies with garden peas • 1857 Louis Pasteur (France) introduces the Germ Theory of Disease. • 1859 Darwin publishes Origin of Species • 1865 Mendel presents presents his results in transmission of phenotypic traits between the generations to the Brünn Society of Natural Sciences. • 1900 Hugo de Vries in Holland, William Bateson in Great Britain, Franz Correns in Germany, and Erich Tschermak in Austria acknowledged Mendel's legacy, and hailed him as the true father of classical genetics. Terms to Know and Use • Gene – A DNA blueprint controlling synthesis of a protein • Trait - variant for a gene: i.e. a purple flower, determined by alleles • Dominant trait - expressed over recessive trait when both are present • Recessive trait - not expressed when the dominant trait is present • Co-Dominant – expressed as blended traits • Allele - a variation of a gene responsible for different traits, often represented as A or a • Locus - location of a gene,or allele, on a chromosome • Chromosome - strand of DNA containing the genes • Haploid - one copy of a chromosome • Diploid - two copies of a chromosome • Gamete - a spermatozoa or oocyte (egg) cell, they are haploid • Zygote - cell resulting from the fusion of two gametes, they are diploid • Genotype - the type of alleles on a chromosome: genetic makeup • Phenotype - The way a genotype is expressed: i.e. the color of a flower • True breeding line - organisms that always pass the same genotype to their offspring • Hybrid - offspring resulting from crossbreeding two true breeding lines: F1 Garden Pea Experiments 1856-64 • Mendel disagreed with the “Blending Theory” of inheritance. • Started with 34 kinds peas Pisium sativum • After 2 years he had 22 purebreds http://www.dnaftb.org/dnaftb/1/concept/index.html Pea Characteristics Trait on the left is dominant. Trait on the right is recessive. Flower Parts Mendel’s Hypotheses • There are alternate forms of ‘genes’=alleles • For each trait, organisms have 2 genes, one from mom & one from dad • Pollen and egg each carry 1 allele/trait because alleles segregate • When only one allele is expressed & other has no noticeable effect, it is dominant • http://www.sumanasinc.com/webcontent/anisamples/ nonmajorsbiology/independentassortment.html Mendel’s Experiments 1. Plants must possess constant differentiating characteristics. 2. The hybrids of such plants must, during the flowering period, be protected from the influence of all foreign pollen, or be easily capable of such protection. 3. The hybrids and their offspring should suffer no marked disturbance in their fertility in the successive generations. Mendel's Laws of Inheritance • Law of Segregation during gamete formation allele pairs separate or segregate, into different gametes (Demonstrated with a “test cross”). • Law of Independent Assortment suggested that each allele pair segregates independently of other gene pairs during gamete formation (Demonstrated with a dihybrid cross). • http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/independentassortment.html Mother contributes: True Breeding A or A A AA AA A AA AA Mother contributes: Cross Breeding a or a A Aa Aa A Aa Aa Monohybrid Cross Test Cross Mendel's Laws of Inheritance • Law of Segregation during gamete formation allele pairs separate or segregate, into different gametes (Demonstrated with a “test cross”). • http://www.sumanasinc.com/webcontent/anisamples/nonmajorsbiology/independentassortment.html • Law of Independent Assortment suggested that each allele pair segregates independently of other gene pairs during gamete formation (Demonstrated with a dihybrid cross). • http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/independentassortment.html Dihybrid Cross Smooth Tall Smooth Tall Smooth wrinkled short Tall wrinkled short Two chromosomes of one parent are represented on the left. Possible alleles passed on to the offspring are on the right. (Consider smooth or wrinkled peas AND tall or short plants) Dihybrid Cross Mother contributes: SB Sb SB SSBB sB sb SSBb SsBB SsBb Sb SSbB SSbb SsbB Ssbb sB sSBB sSBb ssBB ssBb sb sSbB sSbb ssbB ssbb Chromosomes = DNA Meiosis I One diploid sex cell divides…… Meiosis II Result: One diploid cell = four haploid cells Crossing Over in Meiosis I DO ALL GENES ASSORT INDEPENDENTLY? • Genes on the same chromosome tend to be inherited together = linked • Sex-linked genes: color blindness, MD, hemophilia. X Y • X X Credits • • • • • • • • Mendel Image: pw1.netcom.com/~aguldo/ agga/bt/txt/bt1899.htm Pea trellis: http://www.floridata.com/ref/p/images/pisu_sa1.jpg Experiments in Plant Hybridization (1865) by Gregor Mendel Read at the meetings of February 8th, and March 8th, 1865 to the the Natural History Society of Brünn (paper can be read at: http://www.mendelweb.org/home.html MendelWeb, edited by Roger B. Blumberg. (http://www.netspace.org/MendelWeb/, Edition 97.1 1997) The Biology Project: http://www.biology.arizona.edu/default.html Meiosis Images: www.micro.utexas.edu/.../bio304/ genetics/meiosis.4.gif Crossing Over image: http://medlib.med.utah.edu/block2/biochem/Formosa/Figures/Lecture5/515%20Meiosis.JPG Monohybrid, dihybrid, test cross & pea flower: ntri.tamuk.edu/homepagentri/lectures/ biology/test-cross.gi