Mendel

1. Mendel Biology Chapter 10.1 p. 258-268

2. 10.1 Mendel’s Laws of Heredity p. 259-268

3. Gregor Mendel • Austrian monk • Considered the “father of genetics” • The first person to succeed in predicting how traits would be transferred from one generation to another • using the garden pea plant

4. Genetics • The branch of biology that studies heredity • Heredity • The passing on of characteristics from parents to offspring • Traits • Characteristics that are inherited • i.e. eye color, height, etc.

5. Why Mendel chose the garden pea? • Easily cultivated • Short generation time • Reproduces sexually and can be cross-pollinated • Gametes (sex cells) • Male = sperm; female = egg • Pollination • Transfer of the male pollen grains to the pistil of a flower • Fertilization • When the male gamete unites with the female gamete

6. Parts of a Flower

7. Types of Pollination Cross-pollination self-pollination

8. How Mendel studied the garden pea plant? • Controlled his experiments • Studied only one trait at a time • He analyzed his data mathematically • He chose true breeding garden pea plants • Offspring are identical to parents • He studied 7 traits of the garden pea

9. Pea traits that Mendel studied

10. Mendel’s Monohybrid Cross • Hybrid • The offspring of parents that have different forms of a trait, such as tall and short • Monohybrid cross (mono = one) • The two parent plants differed by a single trait – height • P1 – parent generation • F1 –first generation • F2 – second generation P = parent F = “filial” son or daughter

11. Mendel’s Monohybrid Cross • The First Generation • Crossed 2 true breeding plants • 1 tall and 1 short • All offspring of the 2 parent plants were tall P1 X F1

12. Mendel’s Monohybrid Cross • The Second Generation • Self-pollinated the plants from the first generation • ¾ the offspring were as tall as the tall plants in the parent and first generation • ¼ the offspring were as short as the short plant in the parent generation • 3:1 ratio tall to short

13. Second Generation X

14. Mendel’s Monohybrid Cross • The rule of unit factors • Each organism has 2 factors that control each of its traits • These factors are genes • Genes exist in alternative forms called alleles • Ex. Plant height – one alleles is for tall and another is for short • One comes from the mother and one from the father

15. Mendel’s Monohybrid Cross • The rule of dominance • Each trait has an allele that will be observed more than the other • Dominant (gene) • The observed trait • Tall plant • Recessive (gene) • The trait that disappeared • Short plant • Only shows when both alleles are recessive

16. Dominate and Recessive

17. Mendel’s Monohybrid Cross • Recording the results for crosses • Dominate allele is always written first • Uppercase letter is used for dominate • T – tall • Lowercase letter is used for recessive • t – short

18. Mendel’s Monohybrid Cross • Law of segregation • During fertilization, male and female gametes randomly pair to produce 3 combinations of alleles. • Concluded that each plant in the F1 generation carried one dominate allele and one recessive allele and the F2 generation either received 2 dominate; 2 recessive; or one of each

19. Phenotypes and Genotypes • Two organisms can look alike but have different underlying gene combinations • Phenotype • The way an organism looks or behaves • What you see • Genotype • The gene combination an organism contains • The genetic makeup

20. Phenotypes and Genotypes • Homozygous • The two alleles for the trait are the same • TT or tt • Heterozygous • The two alleles for the trait are different • Tt

21. Can you determine the phenotype? • White and purple garden pea flowering plants • Purple is dominate (P) • White is recessive (p)

22. P P P P P P P P P P P P Homozygous Dominate Cross Cross = Purple X Purple

23. p p p p p p p p p p p p Homozygous Recessive Cross Cross = White X White

24. P p P P P p P P p p p p Heterozygous Cross Cross = Purple X Purple

25. Mendel’s Dihybrid Crosses • Cross where the peas differ in 2 traits • Ex. Seed color and Seed shape • A cross involving two traits

26. Mendel’s Dihybrid Crosses • The First Generation • Two true breeding plants (P1) • RRYY = round yellow seed (homozygous dominate) • rryy = wrinkled green seed (homozygous recessive) • When they were crossed all the plants had round yellow seeds (F1)

27. Mendel’s Dihybrid Crosses Dihybrid Cross = round yellow X wrinkled green

28. Mendel’s Dihybrid Crosses • The Second Generation (F2) • Self-pollinated plants from the first generation • Resulted in 9 round yellow, 3 round green, 3 wrinkled yellow, 1 wrinkled green • A ratio of 9:3:3:1

29. Mendel’s Dihybrid Crosses • The law of independent assortment • Genes from different traits are inherited independently of each other • Ex. A pea plant that is RrYy, the alleles will separate and the traits will separate

30. Mendel’s Dihybrid Crosses Heterozygous Cross = round yellow X round yellow

31. Punnett Squares • Devised by an English biologist Reginald Punnett in 1905 • Short hand way of finding the expected ratio of genotypes • The phenotype can also be determined by the Punnett Squares

32. Punnett Squares • Monohybrid crosses • Cross between two plants but only looking at one trait • Alleles of each parent are represented in the cross • One parent is on the top the other is on the side

33. Monohybrid Cross Heterozygous tall parent = Tt Cross = Tt X Tt 

34. Punnett Squares • Dihybrid crosses • Cross between two plants, and you are looking at two traits • Both traits will be represented in the cross • RrYy X RrYy (both are heterozygous)

35. Dihybrid Cross Heterozygous round yellow seed parents = RrYy Cross = RrYy X RrYy 

36. Probability • Genetic is like flipping a coin it can go either way • The Punnett Square is only able to show us the chance/probability that the offspring will be a certain way • All the offspring could be the same PRACTICE PUNNETT SQUARES

37. Monohybrid Punnett Square

38. Dihybrid Punnett Square

39. Dihybrid Punnett Square