Mendelelian Genetics

1. Dr. R. Siva VIT University, INDIA rsiva77in@rediffmail.com Mendelelian Genetics

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

3. 1822 - Brunn in Austria, now, Brno (Czecholovakia) • Financial and Health Problem • Unable to continue studies • Joined St.Augustinian Monastery • 1847 – Priest • 1851 – Higher studies at Vienna • University • 1854- Science teacher

4. 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

5. Gregor Johann Mendel • Austrian monk • Developed the laws of inheritance • Presented his findings in the Natural History Society of Brunn – 1865 • Paper entitled, “Experiments in Plant Hybridization” – 1866 • German language.

6. Mendel's work was not recognized until the turn of the 20th century • 1900 - Carl Correns, Hugo deVries, and Erich von Tschermak rediscover and confirm • Called the “Father of Genetics“

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

8. Mendel’s workplace Fig. 2.5

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

10. 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

11. 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

12. 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)

13. 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)

14. Genotypes • Homozygousgenotype – When the two alleles are same (dominant or 2 recessive genes) e.g. TT or tt; also calledpure  • Heterozygousgenotype – When the 2 alleles are different- one dominant & one recessive allele    (e.g. Tt); also calledhybrid

16. Punnett Square Used to help solve genetics problems

18. Equation • The formula 2n can be used, where “n” = the number of heterozygous traits. • Ex: TtRr, n=2 • 22 or 4 different kinds of gametes are possible. • TR, tR, Tr, tr

19. Dihybrid Cross • TtRr X TtRr • Each parent can produce 4 types of gametes. • TR, Tr, tR, tr • Cross is a 4 X 4 with 16 possible offspring.

20. RESULTS • 9 Tall, Red flowered • 3 Tall, white flowered • 3 short, Red flowered • 1 short, white flowered • Or: 9:3:3:1

21. Genes and Environment Determine Characteristics

22. Mendel’s Pea Plant Experiments

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

24. Reproduction in Flowering Plants • Pollen contains sperm • Produced by the stamen • Ovary contains eggs • Found inside the flower • Pollen carries sperm to the eggs for fertilization • Self-fertilization can occur in the same flower • Cross-fertilization can occur between flowers

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

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

28. 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)

31. Mendel’s Experimental Results

32. Did the observed ratio match the theoretical ratio? 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

33. 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

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

35. Monohybrid Crosses

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

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

38. 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

39. 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

40. What Do the Peas Look Like?

41. …And Now the Test Cross • Mendel then crossed a pure & a hybrid from his F2 generation • This is known as an F2 or test cross • There are two possible testcrosses:Homozygous dominant x HybridHomozygous recessive x Hybrid

42. F2 Monohybrid Cross (1st) • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: RoundseedsxRound seeds • RRx Rr Genotype:RR, Rr Phenotype:Round GenotypicRatio:1:1 PhenotypicRatio: All alike R r RR Rr R R RR Rr

43. F2 Monohybrid Cross (2nd) • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: WrinkledseedsxRound seeds • rrx Rr R r Genotype:Rr, rr Phenotype:Round & Wrinkled G. Ratio:1:1 P.Ratio: 1:1 Rr rr r r Rr rr

44. F2 Monohybrid Cross Review • Homozygous x heterozygous(hybrid) • Offspring:50% Homozygous RR or rr50% HeterozygousRr • Phenotypic Ratio is 1:1 • Called Test Cross because the offspring have SAME genotype as parents

45. Practice Your Crosses • Work the P1, F1, and both F2 Crosses for each of the other Seven Pea Plant Traits

46. Mendel’s Laws1. Law of Dominance2. Law of Segregation3. Law of Independent assortment

47. Law of Dominance States that on crossing homozygous organisms for single pair of contrasting characters, only one characters make its appearance in F1 generation and is name as Dominant character.

48. Results of Monohybrid Crosses • Inheritablefactors or genesare responsible for all heritable characteristics • Phenotype is based on Genotype • Each traitis based ontwo genes, one from the mother and the other from the father • True-breeding individuals are homozygous ( both alleles) are the same

49. Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. All the offspring will be heterozygous and express only the dominant trait. RR x rr yields all Rr (round seeds)

50. Law of Dominance