Mendel's Law of Heredity: Understanding Genetics with Gregor Mendel

1. Section 10.1 - Mendel’s Law of Heredity Ch 10: Mendel and Meiosis

2. Section 10.1 Inside This Section... • Who is Gregor Mendel • Mendel’s Crosses • Phenotypes and Genotypes • Probability in Genetics

3. Section 10.1 Who is Gregor Mendel? • Known as the father of modern genetics • Developed the principles of heredity by studying the variation and heredity of seven pairs of inherited characteristics in pea plants. • The significance of his work was not recognized during his lifetime.

4. Section 10.1 Genetics • Genetics is the branch of biology that studies heredity • Heredity is the passing of characteristics from parents to offspring • Traits are inherited characteristics

5. Section 10.1 More Definitions • Gametes are the sex cells that allow an organism to reproduce • A hybrid is the offspring of parents who have different traits

6. Section 10.1 Reproduction in Peas • Both male and female parts on the same flower • Male gamete is in the pollen grain • Female gamete is in the ovule (located in the pistil)

7. Section 10.1 Reproduction in Peas • Pollination is the transfer of male pollen grains to the pistil • Fertilization happens when the male and female gametes unite

8. F2 Generation F1 Generation Section 10.1 The Generations Parental (P) Generation

9. The Rule of Factors • Each organism has two factors that control each trait • These factors are called genes and are found on the chromosomes and have alternate forms • The different gene forms that control one trait are called alleles

10. Section 10.1 Alleles and Genes

11. Section 10.1 The Rule of Dominance • Dominant: The trait that is more expressive in alleles than other traits (represented by a capital letter) • Recessive: The trait that is submissive in the alleles to the other traits. (Represented by a lowercase letter) • If an organism contains a dominant and a recessive allele, the dominant trait will be expressed TT or Tt tt

12. Section 10.1 The Rule of Dominance • Phenotype is the physical expression of an organism genes • Genotype is the genetic makeup of an organism TT or Tt tt

13. Section 10.1 The Law of Segregation • Alleles separate during meiosis • Each new cell gets one allele for each gene TT or Tt tt

14. Section 10.1 The Law of Independent assortment • All traits are inherited independently from each other

15. Section 10.1 Two types of Crosses • Monohybrid Cross: A cross in which ALL traits are identical except one • Dihybrid Cross: A cross in which two traits differ between organisms

16. Section 10.1 F2 - 3 tall : 1 short F1- All Tall P: Parental Generation Mendel’s Monohybrid Cross • When Mendel crossed tall pea plants with short ones, the first generation (F1) consisted of all tall plants • When he crossed the F1 generation, 3/4 of the F2 generation were tall and 1/4 were short

17. Section 10.1 The Punnett Square T T T t t t • Named after Reginald PunnettUseful for making offspring PredictionsAlleles for 1 parent placed at the top and for the other at the leftEach box is filled with the allele to the top and to the left T T T t t t

18. Mendel’s Dihybrid Cross • When Mendel crossed Round Yellow peas with wrinkled green peas, all of the F1 generation were Round Yellow PeasIn the F2 generation, the following ratios were found:9 Round Yellow3 Round Green3 Wrinkled Yellow1 Wrinkled Green

19. Section 10.1 rryy rrYy Rryy RrYy rrYy rrYY RRYy RrYy Rryy RrYy RRyy RrYy RrYY RrYY RRYy RRYY Mendel’s Dihybrid Cross RrYy * RrYy ry RY Ry rY RY Ry rY ry Probability & Genetics

20. Section 10.1 In Review... • Who is Gregor Mendel • Mendel’s Crosses • Phenotypes and Genotypes • Probability in Genetics

21. Section 10.2 - Meiosis Ch 9: Energy in a Cell

22. Section 10.2 Section 10.2 Inside This Section... • The Two Types of Cells • Chromosomes and Genes • What is Meiosis? • Genetic Recombination

23. Section 10.2 Section 10.2 Two Types of Cells • Diploid: A cell with two of each kind of Chromosomes (both alleles for each gene) • We signify this by writing 2n • All cells in the body except sex cells are diploid • Haploid: A cell with one of each kind of Chromosome (only one allele for each gene)We signify this by writing an ”n”Sex cells are Haploid

24. Section 10.2 Chromosomes and Genes • Chromosomes usually have about a thousand or more genes • Chromosomes occur in pairs • Each chromosome has one allele for a particular gene • Each species contains a characteristic number of chromosomes

25. Section 10.2 Number of Chromosomes

26. Section 10.2 What is Meiosis? • A Process of cell division that results in the production of sex cells (gametes) • Consists of • Interphase: Cell replicates chromosomes • Meiosis I: Results in 2 haploid cells • Meiosis II (similar to mitosis): Results in 4 haploid cells

27. Section 10.2 Meiosis

28. Section 10.2 Meiosis I • Prophase I • Homologous chromosomes come together and form a tetrad (four-part structure) • Sometimes chromosomes exchange genetic material in a process called crossing over

29. Section 10.2

30. Section 10.2 Crossing Over

31. Section 10.2 Meiosis I • Metaphase I • Spindle fibers cause Homologous Chromosomes to line up side by side at the equator

32. Section 10.2

33. Section 10.2 Meiosis I • Anaphase I • Homologous chromosomes separate making each new cell haploid

34. Section 10.2

35. Section 10.2 Meiosis I • Telophase I • Reversal of Prophase I • Spindle breaks down, chromosomes uncoil, cytoplasm divides

36. Section 10.2

37. Section 10.2 Meiosis II • Identical to Mitosis • Results in 4 Haploid cells

38. Section 10.2

39. Section 10.2 Genetic Recombination • Genetic recombination is the source of variation. This is caused by the re-assortment or crossing over during meiosis • 7 pairs of chromosomes = 27 = 128 combinations • Any egg can be fertilized by any sperm, so 128 x 128 = 16,384 possibilities • N=23, 223 = 8,388,608 possibilities • 8,388,608 x 8,388,608 = 7 Trillion possibilities • Crossing over is the exchange of genetic material during prophase I, which results in new combinations of Alleles

40. Section 10.2 In Review... • The Two Types of Cells • Chromosomes and Genes • What is Meiosis? • Genetic Recombination

41. Section 10-3: Mistakes in meiosis Ch 9: Energy in a Cell

42. Section 10.3 Inside This Section... • Nondisjunction • Triploidy and Polyploidy

43. Section 10.3 Nondisjunction • When chromosomes fail to separate during meiosis. • Trisomy: When one gamete gets an extra chromosome, causing the other gamete to be short by one (e.g. Down’s syndrome - trisomy 21) • Monosomy: When one gamete lacks one chromosome

44. Section 10.3 Triploidy and Polyploidy • Triploid is a total lack of separation of homologous chromosomes. • Polyploids are organisms that have more than the normal amount of chromosomes • Rare in animals usually causing death • Frequently occurs in plants causing fruit and flowers to be larger

45. Section 10.3 In Review... • NondisjunctionTriploidy and Polyploidy