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Mendel: The Man


Nathan LeClear

on 3 November 2009

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Transcript of Mendel: The Man

(1707-1778) Versuche uber Pflanzenhybriden
Experiments in Plant Hybridization Gregor Mendel Overview Historical Context
Predecessors and Contemporaries Mendel Rediscovery and Impact Carl von Linne Rudolf-Jakob Camerarius (1665-1721) Joseph Gottlieb Koelreuter (1733-1806) Observed reversion to parental
form during backcross Made close studies of pollen
first palynologist Criticisms and Succesors Carl Friedrich von Gaertner "Transformed" species
through hybridization (1772-1850) Mendel disagreed on the
invariable nature of species Noted the reversion to
parental forms after
backcrossing Believed that hybrids were unnatural Ronald Aylmer Fisher The Man The Experiments Timeline Previous Research Demonstrated the
Sexuality of Plants Seeds failed to develop on corn and
castor bean plants after the male
flowers were removed 1600 1700 1800 Eminent botanist of his day
Struggled greatly to define the boundaries
of species, varieties, and hybrids

Held the belief that new
species were created through
hybridization First to classify plants by the
reproductive structures Developed artificial fertilization techniques
also used by Mendel Contemporaries Charles Naudin (1815-1899) Studied hybridization in
the Cucurbitaceae Did not propose a mechanism
for the "dissolution" to the
parental forms Henri Lecoq (1802-1871) French botanist Director of the Natural History Museum
and Botanical Garden in Paris Mentioned by Mendel in "Versuche" Didn't specialize in a particular group, but
made general observations about
hybridization Charles Darwin (1809-1882) Studied plant
hybridization extensively Noted that hybrids of
varieties tended to be robust
while hybrids of distant
species were sterile First full length case study of
evolution after origin was on
orchids 1900 Mendel: The Man Born Johann Mendel in 1822
Son of peasent farmers Eastern region of Modern Czech republic During his early education he worked at keeping bees
Continued as a monk Became Brother Gregor at the Augustinian Abbey of
St. Thomas in Brno (Brunn) Research Systematic observations of weather for
meterological reports Hybridization studies in Pisum 1868: Elected abbot Died in 1884 due to kidney failure
resulting from chronic stress His papers were burned after his death The Experiments Goals Illuminate the laws dictating progeny form in hybrids Use quantitative experiments to investigate hybridization Setup Selection of a model organism Why Peas? Easily manipulated Short generation Protected from cross pollination Possesses differentiating characteristics True breeding 22 varieties Pisum umbellatum Pisum saccharatum Pisum sativum Progeny must be fertile Selection of characters Perform the crosses Count and describe the progeny Repeat for second, third fourth... generations Hybrids of parents differing in one trait (Monohybrid) Crossed flowers for each trait (n ranged from 23-60) performed Reciprocal crosses Results Conclusions Possible errors Bruchus beetle some flowers aborted < 0.1% First generation resembles one parental form Second generation displays both parental forms
in a near 3:1 ratio No blending of traits were observed Third generation cross of the dominant characteristics Only one third of the self-fertilized dominant trait plants were true breeding From these results he determined that some of the second generations conatin both parental traits
and are therefore the same as all of the first generation hybrid progeny Thus 1:2:1 A Aa a Hybrids of parents differening by more than one characteristic (Dihybrid cross) Begins with what would become his
second law (independent assortment) Results F 1 : all progeny display dominant traits F 2 : four classes in classic 9:3:3:1 calculated the genotypic ratio (1:2:1:2:4:2:1:2:1) F 3 : broke down the hybrid (heterozygotes) from true breeding dominants expected product of the monohybrid genotypic ratio squared Conclusions Each characteristic segregates into
the reproductive cells independently The calculated ratios could be used to
predict the outcome of further crosses Performored a trihybrid cross 2 3 4 n n n individuals classes (genotypes) constant forms (homozygous dominant) i.e. for a tetrahybrid cross 2 3 4 4 4 4 = = = 16 parental forms 81 genotypes 256 individuals The Reproductive cells of the hybrids Determined that pollen and seeds (gametes) contain the hereditary 'factors' Each character separates into individual gametes Independently of other characteristics Predicts that the hereditary factors are present in equal number in the gametes ? ? Backcross (testcross) Crossed F hybrids with true breeding parental forms (reciprocal also) 1 AaBb x AABB AaBb x aabb predicted that there could only be four possible results these would appear in equal numbers In crosses involving the dominant parent type In crosses involving the recessive parent type: all of the offspring would be dominant Other species Phaseolus vulgaris and P. nanus looked at many of the same traits low seed viability resulted in small sample size Saw intermediate forms specifically in flower color there
was a gradient from purple to white Result of polygenetic control Mendel observed that the frequencies
matched those of crosses involving
several traits Rediscovery Hugo de Vries Papaver malevolent towards Mendel Hieracium Carl Correns credited Mendel Zea maize Erich von Tschermak Hordeum Impacts cited only three times prior to 1900 Read at the meeting of the Brunn
Society for Natural History He remained convinced of the
importance of his findings Karl von Nageli Influencial voice convinced of blending Criticisms William Bateson First translation to English coined many modern terms Conflict VS Nikolai Ivanovich Vavilov Trofim Lysenko Questioned the statistical validity of Mendel's experiment Impressed with the elegance of the models Late 20th century statisticians revalidated his findings Magner, L. N. 1994. A History of the Life Sciences 2nd Edition. Marcel Dekker, Inc: New York, NY. Blumberg, R. B. 1997. Mendelweb version 97.1 <www.mendelweb.org> Mendel, G. 1866. Experiments in Plant Hybridization. Proceedings of the Brunn Society of Natural History IV: 3-47 Fairbanks, D. J. and B. Rytting. 2001. Mendelian Controversies: A Botanical and Historical Review. American Journal of Botany 85(5): 737-752. Pringle, P. 2008. The Murder of Nikolai Vavilov. Simon & Schuster New York, NY. 2000 Today Integral part of modern biology education At the monastery he created
hybrids of bees the could be
considered some of the first
Africanized honey bees Discussion:
Are major scientific breakthroughs products of singular briliance?

Are you suspicious of Mendel's findings?
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