1. Introduction to Genetics Chapter 11 Copyright Pearson Prentice Hall

2. 11-1 The Work of Gregor Mendel del Copyright Pearson Prentice Hall

3. Gregor Mendel’s Peas Genetics is the scientific study of heredity. Gregor Mendel was an Austrian monk. His work was important to the understanding of heredity. Mendel carried out his work with ordinary garden peas. Copyright Pearson Prentice Hall Gregor Mendel’s Peas

4. Mendel knew that the male part of each flower produces pollen, (containing sperm). the female part of the flower produces egg cells. Copyright Pearson Prentice Hall

5. Gregor Mendel’s Peas During sexual reproduction, sperm and egg cells join in a process called fertilization. Fertilization produces a new cell. Pea flowers are self-pollinating. Copyright Pearson Prentice Hall

6. Mendel had true-breeding pea plants that, if allowed to self-pollinate, would produce offspring identical to themselves. Copyright Pearson Prentice Hall Cross-pollination Mendel was able to produce seeds that had two different parents.

7. Each original pair of plants is the P (parental) generation. The offspring are called the F 1, or “first filial,” generation. The offspring of crosses between parents with different traits are called hybrids. Copyright Pearson Prentice Hall

8. Genes and Dominance Copyright Pearson Prentice Hall Mendel’s F 1 Crosses on Pea Plants

9. Genes and Dominance Copyright Pearson Prentice Hall Mendel’s Seven F 1 Crosses on Pea Plants Mendel’s F 1 Crosses on Pea Plants

10. Genes and Dominance Mendel's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next. Today, scientists call the factors that determine traits genes. Copyright Pearson Prentice Hall

11. Genes and Dominance Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait. The different forms of a gene are called alleles. Mendel’s second conclusion is called the principle of dominance. Copyright Pearson Prentice Hall

12. The principle of dominance states that some alleles are dominant and others are recessive. Copyright Pearson Prentice Hall

13. Genes and Dominance Copyright Pearson Prentice Hall Mendel’s F 1 Crosses on Pea Plants

14. Segregation Mendel crossed the F 1 generation with itself to produce the F 2 (second filial) generation. The traits controlled by recessive alleles reappeared in one fourth of the F 2 plants. Copyright Pearson Prentice Hall

15. Segregation Mendel's F 2 Generation Copyright Pearson Prentice Hall P Generation F 1 Generation Tall Short F 2 Generation

16. The reappearance of the trait controlled by the recessive allele indicated that at some point the allele for shortness had been separated, or segregated, from the allele for tallness. Copyright Pearson Prentice Hall

17. Mendel suggested that the alleles for tallness and shortness in the F 1 plants segregated from each other during the formation of the sex cells, or gametes. Copyright Pearson Prentice Hall

18. Alleles separate during gamete formation. Copyright Pearson Prentice Hall

19. 11-2 Probability and Punnett Square Copyright Pearson Prentice Hall

20. Genetics and Probability The likelihood that a particular event will occur is called probability. The principles of probability can be used to predict the outcomes of genetic crosses. Copyright Pearson Prentice Hall

21. Punnett Squares The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square. Punnett squares can be used to predict and compare the genetic variations that will result from a cross. Copyright Pearson Prentice Hall

22. Punnett Squares A capital letter represents the dominant allele for tall. A lowercase letter represents the recessive allele for short. In this example, T = tall t = short Copyright Pearson Prentice Hall

23. Punnett Squares Gametes produced by each F 1 parent are shown along the top and left side. Copyright Pearson Prentice Hall

24. Punnett Squares Organisms that have two identical alleles for a particular trait are said to be homozygous. Organisms that have two different alleles for the same trait are heterozygous. Homozygous organisms are true-breeding for a particular trait. Heterozygous organisms are hybrid for a particular trait. Copyright Pearson Prentice Hall

25. Punnett Squares All of the tall plants have the same phenotype, or physical characteristics. The tall plants do not have the same genotype, or genetic makeup. One third of the tall plants are TT, while two thirds of the tall plants are Tt. Copyright Pearson Prentice Hall

26. Punnett Squares The plants have different genotypes (TT and Tt), but they have the same phenotype (tall). Copyright Pearson Prentice Hall TT Homozygous Tt Heterozygous

27. Probability and Segregation One fourth (1/4) of the F 2 plants have two alleles for tallness (TT). 2/4 or 1/2 have one allele for tall (T), and one for short (t). One fourth (1/4) of the F 2 have two alleles for short (tt). Copyright Pearson Prentice Hall

28. Probabilities Predict Averages Probabilities predict the average outcome of a large number of events. Probability cannot predict the precise outcome of an individual event. In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values. Copyright Pearson Prentice Hall

29. 11–3 Exploring Mendelian Genetics eti Copyright Pearson Prentice Hall

30. Independent Assortment To determine if the segregation of one pair of alleles affects the segregation of another pair of alleles, Mendel performed a two-factor cross. Copyright Pearson Prentice Hall

31. Independent Assortment The Two-Factor Cross: F 1 Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy). RRYY x rryy All of the F 1 offspring produced round yellow peas (RrYy). Copyright Pearson Prentice Hall

32. Independent Assortment The alleles for round (R) and yellow (Y) are dominant over the alleles for wrinkled (r) and green (y). Copyright Pearson Prentice Hall

33. Independent Assortment The Two-Factor Cross: F 2 Mendel crossed the heterozygous F 1 plants (RrYy) with each other to determine if the alleles would segregate from each other in the F 2 generation. RrYy × RrYy Copyright Pearson Prentice Hall

34. Independent Assortment The Punnett square predicts a 9 : 3 : 3 :1 ratio in the F 2 generation. Copyright Pearson Prentice Hall Represents: Independent Assortment

35. The alleles for seed shape segregated independently of those for seed color. This principle is known as independent assortment. Genes that segregate independently do not influence each other's inheritance. Copyright Pearson Prentice Hall

36. Independent Assortment principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes. Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms. Copyright Pearson Prentice Hall

37. A Summary of Mendel's Principles Genes are passed from parents to their offspring. If two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. Copyright Pearson Prentice Hall

38. A Summary of Mendel's Principles In most sexually reproducing organisms, each adult has two copies of each gene. These genes are segregated from each other when gametes are formed. The alleles for different genes usually segregate independently of one another. Copyright Pearson Prentice Hall

39. Beyond Dominant and Recessive Alleles Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. Copyright Pearson Prentice Hall

40. Beyond Dominant and Recessive Alleles Incomplete Dominance When one allele is not completely dominant over another it is called incomplete dominance. In incomplete dominance, the heterozygous phenotype is between the two homozygous phenotypes. Copyright Pearson Prentice Hall

41. Beyond Dominant and Recessive Alleles A cross between red (RR) and white (WW) four o’clock plants produces pink-colored flowers (RW). Copyright Pearson Prentice Hall WW RR

42. Beyond Dominant and Recessive Alleles Codominance In codominance, both alleles contribute to the phenotype. In certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers. Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately. Copyright Pearson Prentice Hall

43. Beyond Dominant and Recessive Alleles Multiple Alleles Genes that are controlled by more than two alleles are said to have multiple alleles. An individual can’t have more than two alleles. However, more than two possible alleles can exist in a population. A rabbit's coat color is determined by a single gene that has at least four different alleles. Copyright Pearson Prentice Hall

44. Different combinations of alleles result in the colors shown here. Copyright Pearson Prentice Hall Full color: CC, Cc ch, Cc h, or Cc Chinchilla: c ch c h, c ch c ch, or c ch cHimalayan: c h c, or c h c h AIbino: cc KEY C = full color; dominant to all other alleles c ch = chinchilla; partial defect in pigmentation; dominant to c h and c alleles c h = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles

46. Polygenic Traits Traits controlled by two or more genes are said to be polygenic traits. Skin color in humans is a polygenic trait controlled by more than four different genes. Copyright Pearson Prentice Hall

47. aabbccAabbccAaBbccAaBbCcAABbCcAABBCcAABBCC AaBbCc 20 / 64 15 / 64 6 / 64 1 / 64 Fraction of progeny

48. Applying Mendel's Principles Thomas Hunt Morgan used fruit flies to advance the study of genetics. Morgan and others tested Mendel’s principles and learned that they applied to other organisms as well as plants. Copyright Pearson Prentice Hall

49. 11-4 Meiosis Copyright Pearson Prentice Hall

50. Each organism must inherit a single copy of every gene from each of its “parents.” Gametes are formed by a process that separates the two sets of genes so that each gamete ends up with just one set. Copyright Pearson Prentice Hall

51. Chromosome Number All organisms have different numbers of chromosomes. A body cell in an adult fruit fly has 8 chromosomes: 4 from the fruit fly's male parent, and 4 from its female parent. Copyright Pearson Prentice Hall

52. These sets of chromosomes are homologous. Each of the 4 chromosomes that came from the male parent has a corresponding chromosome from the female parent. Copyright Pearson Prentice Hall

53. A cell that contains both sets of homologous chromosomes is said to be diploid. The number of chromosomes in a diploid cell is sometimes represented by the symbol 2N. For Drosophila, the diploid number is 8, which can be written as 2N=8. Copyright Pearson Prentice Hall

54. The gametes of sexually reproducing organisms contain only a single set of chromosomes, and therefore only a single set of genes. These cells are haploid. Haploid cells are represented by the symbol N. For Drosophila, the haploid number is 4, which can be written as N=4. Copyright Pearson Prentice Hall

55. Phases of Meiosis Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. Copyright Pearson Prentice Hall

56. Meiosis involves two divisions, meiosis I and meiosis II. By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells. Copyright Pearson Prentice Hall

57. Meiosis I Copyright Pearson Prentice Hall Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Interphase I Meiosis I

58. Cells undergo a round of DNA replication, forming duplicate chromosomes. Copyright Pearson Prentice Hall Interphase I

59. Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. There are 4 chromatids in a tetrad. Copyright Pearson Prentice Hall MEIOSIS I I Prophase I

60. When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over. Crossing-over produces new combinations of alleles. Copyright Pearson Prentice Hall

61. Spindle fibers attach to the chromosomes. Copyright Pearson Prentice Hall MEIOSIS I Metaphase I

62. The fibers pull the homologous chromosomes toward opposite ends of the cell. Copyright Pearson Prentice Hall MEIOSIS I Anaphase I

63. Nuclear membranes form. The cell separates into two cells. The two cells produced by meiosis I have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I. Copyright Pearson Prentice Hall MEIOSIS I Telophase I and Cytokinesis

64. Meiosis II The two cells produced by meiosis I now enter a second meiotic division. Unlike meiosis I, neither cell goes through chromosome replication. Each of the cell’s chromosomes has 2 chromatids. Copyright Pearson Prentice Hall

65. Phases of Meiosis Meiosis II Copyright Pearson Prentice Hall Telophase II and Cytokinesis Prophase II Metaphase II Anaphase II Telophase I and Cytokinesis I Meiosis II

66. Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell. Copyright Pearson Prentice Hall MEIOSIS II Prophase II

67. The chromosomes line up in the center of cell. Copyright Pearson Prentice Hall MEIOSIS II Metaphase II

68. The sister chromatids separate and move toward opposite ends of the cell. Copyright Pearson Prentice Hall MEIOSIS II Anaphase II

69. Meiosis II results in four haploid (N) daughter cells. Copyright Pearson Prentice Hall MEIOSIS II Telophase II and Cytokinesis

70. Gamete Formation In male animals, meiosis results in four equal-sized gametes called sperm. Copyright Pearson Prentice Hall

71. In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction. Copyright Pearson Prentice Hall

72. Comparing Mitosis and Meiosis Mitosis results in the production of two genetically identical diploid cells. Meiosis produces four genetically different haploid cells. Copyright Pearson Prentice Hall

73. Comparing Mitosis and Meiosis Mitosis Cells produced by mitosis have the same number of chromosomes and alleles as the original cell. Mitosis allows an organism to grow and replace cells. Some organisms reproduce asexually by mitosis. Copyright Pearson Prentice Hall

74. Meiosis Cells produced by meiosis have half the number of chromosomes as the parent cell. These cells are genetically different from the diploid cell and from each other. Meiosis is how sexually-reproducing organisms produce gametes. Copyright Pearson Prentice Hall