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Gregor Johann Mendel

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  1. 1822- 1884 Austrian monk Experimented with pea plants He thought that ‘heritable factors’ (genes) retained their individuality generation after generation Gregor Johann Mendel

  2. 1831 Charles Darwin joins crew of Beagle 1847Semmelweiss 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. Time Line

  3. Terms to Know and Use • Gene - a heritable feature: i.e. flower color coded for on a chromosome • 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

  4. Allele - a variation of a gene responsible for different traits, often expressed as A or a • Locus - location of a gene,or allele, on a chromosome • Chromosome - strand of DNA that codes for genes • Haploid - one copy of a chromosome • Diploid - two copies of a chromosome • Gamete - a spermatozoa or oocyte (egg) cell, they are haploid

  5. 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

  6. Garden Pea Experiments 1856-64 • Mendel disagreed with the “Blending Theory” of inheritance. • Started with34 kinds peas Pisium sativum • After 2 years he had 22 purebreds http://www.dnaftb.org/dnaftb/1/concept/index.html

  7. Pea Characteristics Trait on the left is dominant. Trait on the right is recessive.

  8. Flower Parts

  9. Mendel’s Hypotheses • There are alternate forms of ‘genes’=alleles • For each trait, organisms have 2 genes, one from mom & one from dad • Sperm 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

  10. Mendel’s Experiments • Plants must possess constant differentiating characteristics. • 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. • The hybrids and their offspring should suffer no marked disturbance in their fertility in the successive generations.

  11. Mendel's Laws of Inheritance • Law of Segregationduring 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

  12. Mother contributes: True Breeding A A or A AA AA or Father contributes: AA AA A

  13. Mother contributes: Cross Breeding a a or A Aa Aa or Father contributes: Aa Aa A

  14. Monohybrid Cross

  15. Test Cross

  16. 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 Assortmentsuggested 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

  17. Dihybrid Cross

  18. wrinkled wrinkled Smooth Smooth Smooth Tall Tall short Tall 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)

  19. Mother contributes: Dihybrid Cross SB Sb sB sb SB SsBb SSBB SSBb SsBB Sb SSbB SsbB Ssbb SSbb Father contributes: sB sSBB sSBb ssBB ssBb sb sSbB sSbb ssbB ssbb

  20. Chromosomes = DNA

  21. Meiosis I One diploid sex cell divides……

  22. Meiosis II Result: One diploid cell = four haploid cells

  23. Crossing Over in Meiosis I

  24. 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

  25. 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/Lecture5/5-15%20Meiosis.JPG • Monohybrid, dihybrid, test cross & pea flower: ntri.tamuk.edu/homepage-ntri/lectures/ biology/test-cross.gi

  26. Who Cares About Genetics?

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