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M endelian Genetics

M endelian Genetics. GREGOR MENDEL. Austrian Monk Father of Genetics Pea Plant Experiments (1858-1868). Site of Gregor Mendel’s experiment - a garden in the Czech Republic. Mendel ’ s workplace. Fig. 2.5. Mendel stated that physical traits are inherited as “particles”

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M endelian Genetics

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  1. Mendelian Genetics

  2. GREGOR MENDEL • Austrian Monk • Father of Genetics • Pea Plant Experiments (1858-1868)

  3. Site of Gregor Mendel’s experiment - a garden in the Czech Republic

  4. Mendel’s workplace Fig. 2.5

  5. Mendel stated that physical traits are inherited as “particles” Mendel did not know that the “particles” were actually Chromosomes & DNA

  6. Terms you need to know: • Trait - any characteristic that can be passed from parent to offspring • Heredity - passing of traits from parent to offspring • Monohybrid cross - cross involving a single traite.g. flower color • Dihybrid cross - cross involving two traits e.g. flower color & plant height

  7. Terms you need to know: • Alleles - two forms of a gene (dominant & recessive) • Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R) • Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r) • Genotype - gene combination for a trait (e.g. RR, Rr, rr) • Phenotype - the physical feature resulting from a genotype (e.g. red, white)

  8. Terms you need to know: • Homozygous genotype – When the two alleles are same (2 dominant or 2 recessive genes) e.g. TT or tt; also called pure  • Heterozygous genotype – When the 2 alleles are different- one dominant & one recessive allele    (e.g. Tt);

  9. Parental P1 Generation= the parental generation in a breeding experiment. • F1 generation= the first-generation offspring in a breeding experiment. (1st filial generation) • From breeding individuals from the P1 generation • F2 generation= the second-generation offspring in a breeding experiment. (2nd filial generation) • From breeding individuals from the F1 generation

  10. Mendel’s Pea Plant Experiments

  11. Why peas,Pisum sativum? • Can be grown in a small area • Produce lots of offspring • Several generations in a season • Produce pure plants when allowed to self-pollinate • Can be artificially cross-pollinated • Many traits known • Above all, easy to grow

  12. Reproduction in Flowering Plants • Pollen contains sperm. Pollen is found on the stamen • Ovary contains eggs. Found inside the flower. Turns into fruit after fertilization of the egg cells by sperm.

  13. Mendel hand-pollinated flowers using a paintbrush. He could snip (cut) the stamens to prevent self-pollination He kept detailed records to trace traits through the several generations Mendel’s Experimental Methods

  14. How Mendel Began Mendel produced pure strains by allowing the plants to self-pollinate for several generations

  15. Eight Pea Plant Traits • Seed shape --- Round (R) or Wrinkled (r) • Seed Color ---- Yellow (Y) or  Green (y) • Pod Shape --- Smooth (S) or wrinkled (s) • Pod Color ---  Green (G) or Yellow (g) • Seed Coat Color ---Gray (G) or White (g) • Flower position---Axial (A) or Terminal (a) • Plant Height --- Tall (T) or Short (t) • Flower color --- Purple (P) or white (p)

  16. Monohybrid Crosses

  17. Punnett Square • Used to help solve genetics problems

  18. P1 Monohybrid Cross • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: RoundseedsxWrinkled seeds • RR x rr Genotype:Rr Phenotype:Round GenotypicRatio:All alike PhenotypicRatio: All alike r r Rr Rr R R Rr Rr

  19. F1 Monohybrid Cross • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: Roundseeds xRound seeds • Rrx Rr Genotype:RR, Rr, rr Phenotype:Round & wrinkled G.Ratio:1:2:1 P.Ratio: 3:1 R r RR Rr R r Rr rr

  20. F1 Monohybrid Cross Review • Heterozygous x heterozygous • Offspring:25% Homozygous dominantRR50% HeterozygousRr25% Homozygous Recessiverr • Offspring calledF2 generation • Genotypic ratio is1:2:1 • Phenotypic Ratio is 3:1

  21. What Do the Peas Look Like?

  22. The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled Mendel’s observed ratio was 2.96:1 The discrepancy is due to statistical error The larger the sample the more nearly the results approximate to the theoretical ratio • Did the observed ratio match the theoretical ratio?

  23. Dihybrid Cross Yellow, RoundxYellow, Round • YyRrXYyRr • Each parent can produce 4 types of gametes. • YR, Yr, yR, yr • Cross is a 4 X 4 with 16 possible offspring.

  24. RY Ry rY ry RY Ry rY ry Dihybrid Cross

  25. RY Ry rY ry Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy 9:3:3:1 phenotypic ratio Dihybrid Cross

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