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The Work of Gregor Mendel

The Work of Gregor Mendel. An Introduction to Genetics. Genetics. Genetics is everywhere these days – and it will continue as a dominant force in Biology and society for decades to come! Defined : as the scientific study of heredity

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The Work of Gregor Mendel

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  1. The Work of Gregor Mendel An Introduction to Genetics

  2. Genetics • Genetics is everywhere these days – and it will continue as a dominant force in Biology and society for decades to come! • Defined: as the scientific study of heredity • It is now the core of a revolution in understanding biology

  3. Gregor Mendel Monk at St Thomas Abbey in Brno of the Czech Republic Studied garden peas from 1856-63 Published his 'paper' in 1866 Pretty much ignored until 1900 That year 3 scientists independently came to many of the same ideas His experiments were special because: 1) Quantitative 2) carefully documented 3) elegantly designed

  4. Gregor Mendel Breeding for traits was long established. Cross (or mating) -- sexual reproduction between 2 organisms Hybrid-- cross between 2 parents which differ in some trait Phenotype-- observable difference between 2 members of the species Genotype-- relationship between genes; the genetic make-up True breeding-- only produce their own phenotype when bred to self 2 key features of Mendel's work: could pollinate from specific parents chose unambiguous phenotypes that were easy to identify

  5. Genes and Dominance • Mendel studied 7 different pea plant traits • Trait – specific characteristic that varies from one individual to another • Example: seed color, or plant height

  6. Mendelian Genetics Some terminology: Parental generations (P0 or F0)-- originally crossed organisms F1 generation-- “first filial”, the offspring of the F0 generation (parents) Hybrid– offspring of crosses between parents with different traits F2 generation-- offspring of F1 generation crossed to itself Dominant-- phenotype visible in the F1 generation Recessive-- trait which reappears in the F2 generation after self cross

  7. Genes, Alleles, and Chromosomes • Genes – are the chemical factors that determine traits • Alleles – the different forms of a gene • Homozygous – organisms carrying two copies of the same allele( i.e. TT or tt ) • Heterozygous – organism carrying different alleles of the same gene (i.e. Tt )

  8. Mendelian Genetics x P0 green yellow ratio F1 generation 227 0 F2 generation 593 193 3.07 In this case, green is dominant, yellow is recessive

  9. Mendelian Genetics Importantly, Mendel went another step further looking at F3 plants 593 crosses 201 green offspring only 392 green and yellow F3 3:1 ratio green: yellow 193 crosses 193 yellow offspring only 0 green pea pods Overall 1/4 F2 matings green, 1/2 F2 matings mixed, 1/4 F2 matings yellow 1:2:1 ratio for all F2 crosses

  10. Mendelian Genetics More terminology: Gamete-- reproductive cell Zygote-- fertilized egg From the ratios above Mendel determined each plant has 2 genetic determinants these determinants go to each offspring randomly Mendel's Principle of Segregation: In the formation of gametes, the paired hereditary determinants separate such that each gamete is equally likely to contain either one. note: gametes have 1 "determinant" zygotes and adults have 2 Capitalized traits = dominant phenotypes lowercase traits= recessive phenotypes ** most mutations are recessive adult gamete zygote

  11. Mendelian Genetics Classical Punett's Square is a way to determine ways traits can segregate They can be used to predict and compare the genetic variations that will result from the cross. Parental P0 cross F1 cross Test cross: mating to a homozygous recessive individual

  12. Mendelian Genetics dihybrid cross-- parental generation differs in two traits example-cross violet/axial flowers with white/terminal ones Violet/axial is dominant, so F1 is all violet axial. What about F2? VV AA VV Aa Vv AA Vv Aa VV Aa VV aa Vv Aa Vv aa Vv AA Vv Aa vv AA vv Aa Vv Aa Vv aa vv Aa vv aa

  13. Mendelian Genetics Principle of Independent Assortment: segregation of any pair of alleles is independent of other pairs in the formation of gametes; genes for different traits can segregate independently during the formation of gametes Accounts for the many genetic variations observed in plants, animals and other organisms. adult gametes

  14. Mendelian Genetics test cross: F1 generation crossed to double homozygous recessive Vv Aa Vv Aa Vv Aa Vv Aa Vv aa Vv aa Vv aa Vv aa vv Aa vv Aa vv Aa vv Aa vv aa vv aa vv aa vv aa What are the expected phenotype ratios in the testcross generation? violet, axial = violet, terminal = white, axial = white, terminal = 1/4 1/4 1/4 1/4 A test cross gives the ratio of gametes in the F1 generation

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