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Mendelelian Genetics

Mendelelian Genetics. Gregor Mendel (1822-1884). Responsible for the Laws governing Inheritance of Traits. Gregor Johann Mendel. Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants He found that the plants' offspring retained traits of the parents

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Mendelelian Genetics

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  1. Mendelelian Genetics

  2. Gregor Mendel(1822-1884) Responsible for the Laws governing Inheritance of Traits

  3. Gregor Johann Mendel • Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants • He found that the plants' offspring retained traits of the parents • Called the “Father of Genetics"

  4. Site of Gregor Mendel’s experimental garden in the Czech Republic

  5. Genetic Terminology • Trait - any characteristic that can be passed from parent to offspring • Heredity - passing of traits from parent to offspring • Genetics - study of heredity

  6. Types of Genetic Crosses • Monohybrid cross - cross involving a single traite.g. flower color • Dihybrid cross - cross involving two traits e.g. flower color & plant height

  7. Designer “Genes” • Alleles - two forms of a gene (dominant & recessive) • Dominant - stronger of two genes expressed in the hybrid; represented byacapital letter (R) • Recessive - gene that shows up less often in a cross; represented by alowercase letter (r)

  8. More Terminology • Genotype - gene combination for a trait(e.g. RR, Rr, rr) • Phenotype - the physical feature resulting from a genotype(e.g. red, white)

  9. Genotypes • Homozygousgenotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also calledpure  • Heterozygousgenotype - gene combination of one dominant & one recessive allele    (e.g. Rr); also calledhybrid

  10. Genotype & Phenotype in Flowers Genotype of alleles:R= red flowerr= yellow flower All genes occur in pairs, so 2alleles affect a characteristic Possible combinations are: GenotypesRRRrrr PhenotypesRED RED YELLOW

  11. Punnett Square Used to help solve genetics problems

  12. Generation “Gap” • 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

  13. Following the Generations Cross 2 Pure PlantsTT x tt Results in all HybridsTt Cross 2 Hybridsget3 Tall & 1 ShortTT, Tt, tt

  14. Monohybrid Crosses

  15. P1 Monohybrid Cross • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: RoundseedsxWrinkled seeds • RRx rr Genotype:Rr Phenotype:Round GenotypicRatio:All alike (100%) PhenotypicRatio: All alike (100%) r r Rr Rr R R Rr Rr

  16. P1 Monohybrid Cross Review • Homozygous dominant x Homozygous recessive • OffspringallHeterozygous(hybrids) • Offspring calledF1 generation • Genotypic & Phenotypic ratio isALL ALIKE

  17. 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

  18. 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

  19. Mendel’s Laws

  20. Law of Dominance One trait is dominant over the other

  21. Law of Segregation Alleles separate during gamete formation

  22. Law of Independent Assortment • Alleles for differenttraits are distributed to sex cells (& offspring) independently of one another.

  23. Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tttall x short 100% Tt tall SEGREGATION Tt x Tttall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGground & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods

  24. Dihybrid Cross • A breeding experiment that tracks the inheritance of two traits. • Mendel’s “Law of Independent Assortment”

  25. Dihybrid Cross • Traits: Seed shape & Seed color • Alleles:R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations

  26. Dihybrid Cross RY Ry rY ry RY Ry rY ry

  27. Dihybrid Cross 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

  28. Incomplete Dominance

  29. Incomplete Dominance r r R R • F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. • Example:snapdragons (flower) • red (RR) x white (rr) • RR = red flower • rr = white flower

  30. Incomplete Dominance r produces the F1 generation Rr Rr R R Rr Rr All Rr = pink (heterozygous pink) r

  31. Incomplete Dominance

  32. Genetic Practice Problems

  33. Breed the P1 generation t t T T • tall (TT) x dwarf (tt) pea plants

  34. Solution: t t produces the F1 generation Tt Tt T Tt Tt T All Tt = tall (heterozygous tall) tall (TT) vs. dwarf (tt) pea plants

  35. Breed the F1 generation T t T t • tall (Tt) vs. tall (Tt) pea plants

  36. Solution: T t produces the F2 generation Tt TT T 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt Tt tt t 1:2:1 genotype 3:1 phenotype tall (Tt) x tall (Tt) pea plants

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