1. Copyright Pearson Prentice Hall 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. Gregor Mendel’s Peas

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

3. Copyright Pearson Prentice Hall 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.

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

5. Copyright Pearson Prentice Hall Genes and Dominance A trait is a specific characteristic that varies from one individual to another. Mendel studied seven pea plant traits, each with two contrasting characters. He crossed plants with each of the seven contrasting characters and studied their offspring.

6. Copyright Pearson Prentice Hall Genes and Dominance 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.

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

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

9. Copyright Pearson Prentice Hall 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.

10. Copyright Pearson Prentice Hall 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.

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

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

13. Copyright Pearson Prentice Hall 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.

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

15. Copyright Pearson Prentice Hall Segregation 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.

16. Copyright Pearson Prentice Hall Segregation 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.

17. Copyright Pearson Prentice Hall Segregation Alleles separate during gamete formation.

18. Copyright Pearson Prentice Hall 11-1 Gametes are also known as a.genes. b.sex cells. c.alleles. d.hybrids.

19. Copyright Pearson Prentice Hall 11-1 The offspring of crosses between parents with different traits are called a.alleles. b.hybrids. c.gametes. d.dominant.

20. Copyright Pearson Prentice Hall 11-1 In Mendel’s pea experiments, the male gametes are the a.eggs. b.seeds. c.pollen. d.sperm.

21. Copyright Pearson Prentice Hall 11-1 In a cross of a true-breeding tall pea plant with a true-breeding short pea plant, the F 1 generation consists of a.all short plants. b.all tall plants. c.half tall plants and half short plants. d.all plants of intermediate height.

22. Copyright Pearson Prentice Hall 11-1 If a particular form of a trait is always present when the allele controlling it is present, then the allele must be a.mixed. b.recessive. c.hybrid. d.dominant.

23. Copyright Pearson Prentice Hall 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.

24. Copyright Pearson Prentice Hall 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.

25. Copyright Pearson Prentice Hall 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 Punnett Squares

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

27. Copyright Pearson Prentice Hall 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.

28. Copyright Pearson Prentice Hall 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.

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

30. Copyright Pearson Prentice Hall 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).

31. Copyright Pearson Prentice Hall 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.

32. Copyright Pearson Prentice Hall 11-2 Probability can be used to predict a.average outcome of many events. b.precise outcome of any event. c.how many offspring a cross will produce. d.which organisms will mate with each other.

33. Copyright Pearson Prentice Hall 11-2 Compared to 4 flips of a coin, 400 flips of the coin is a.more likely to produce about 50% heads and 50% tails. b.less likely to produce about 50% heads and 50% tails. c.guaranteed to produce exactly 50% heads and 50% tails. d.equally likely to produce about 50% heads and 50% tails.

34. Copyright Pearson Prentice Hall 11-2 Organisms that have two different alleles for a particular trait are said to be a.hybrid. b.heterozygous. c.homozygous. d.recessive.

35. Copyright Pearson Prentice Hall 11-2 Two F 1 plants that are homozygous for shortness are crossed. What percentage of the offspring will be tall? a.100% b.50% c.0% d.25%

36. Copyright Pearson Prentice Hall 11-2 The Punnett square allows you to predict a.only the phenotypes of the offspring from a cross. b.only the genotypes of the offspring from a cross. c.both the genotypes and the phenotypes from a cross. d.neither the genotypes nor the phenotypes from a cross.

37. Copyright Pearson Prentice Hall 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. Independent Assortment

38. Copyright Pearson Prentice Hall 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).

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

40. Copyright Pearson Prentice Hall 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

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

42. Copyright Pearson Prentice Hall 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. Independent Assortment

43. Copyright Pearson Prentice Hall The 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. Indepen dent Assort ment

44. Copyright Pearson Prentice Hall 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.

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

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

47. Copyright Pearson Prentice Hall 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.

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

49. Copyright Pearson Prentice Hall 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.

50. Copyright Pearson Prentice Hall 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.

52. Copyright Pearson Prentice Hall Beyond Dominant and Recessive Alleles Different combinations of alleles result in the colors shown here. 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

53. Epista sis A trait involves 2 genes The expression of one gene influences the expression of the other For example, in Labrador Retrievers one gene determines which color. A different gene determines if you have color. E=have color in hair, e=no color in hair B=black pigment, b=brown pigment

54. Fig. 10.13, p.161 EBEbeBeb EB Eb eB eb EeBb black EeBB black EEBb black EEBB black EEBb black EeBB black EeBb black Eebb chocolate EeBb black EEbb chocolate EeBb black Eebb chocolate eeBB yellow eeBb yellow eebb yellow eeBb yellow

55. Copyright Pearson Prentice Hall Beyond Dominant and Recessive Alleles 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.

56. LE 14-12 aabbccAabbccAaBbccAaBbCcAABbCcAABBCcAABBCC AaBbCc 20 / 64 15 / 64 6 / 64 1 / 64 Fraction of progeny

57. Copyright Pearson Prentice Hall 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.

58. Copyright Pearson Prentice Hall 11–3 In a cross involving two pea plant traits, observation of a 9 : 3 : 3 : 1 ratio in the F 2 generation is evidence for a.the two traits being inherited together. b.an outcome that depends on the sex of the parent plants. c.the two traits being inherited independently of each other. d.multiple genes being responsible for each trait.

59. Copyright Pearson Prentice Hall 11–3 Traits controlled by two or more genes are called a.multiple-allele traits. b.polygenic traits. c.codominant traits. d.hybrid traits.

60. Copyright Pearson Prentice Hall 11–3 In four o'clock flowers, the alleles for red flowers and white flowers show incomplete dominance. Heterozygous four o'clock plants have a.pink flowers. b.white flowers. c.half white flowers and half red flowers. d.red flowers.

61. Copyright Pearson Prentice Hall 11–3 A white male horse and a tan female horse produce an offspring that has large areas of white coat and large areas of tan coat. This is an example of a.incomplete dominance. b.multiple alleles. c.codominance. d.a polygenic trait.

62. Copyright Pearson Prentice Hall 11–3 Mendel's principles apply to a.pea plants only. b.fruit flies only. c.all organisms. d.only plants and animals.

63. Copyright Pearson Prentice Hall 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.

64. Copyright Pearson Prentice Hall Chromo some 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.

65. Copyright Pearson Prentice Hall Chromo some Number 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.

66. Copyright Pearson Prentice Hall Chromo some Number 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.

67. Copyright Pearson Prentice Hall Chromo some Number 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.

68. Copyright Pearson Prentice Hall 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.

69. Copyright Pearson Prentice Hall 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. Phases of Meiosis

70. Copyright Pearson Prentice Hall Phases of Meiosis Meiosis I Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Interphase I Meiosis I

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

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

73. Copyright Pearson Prentice Hall Phases of Meiosis 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.

74. Copyright Pearson Prentice Hall Phases of Meiosis Spindle fibers attach to the chromosomes. MEIOSIS I Metaphase I

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

76. Copyright Pearson Prentice Hall Phases of Meiosis MEIOSIS I Telophase I and Cytokinesis 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.

77. Copyright Pearson Prentice Hall Phases of Meiosis 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.

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

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

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

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

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

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

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

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

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

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

88. Copyright Pearson Prentice Hall 11-4 If the body cells of humans contain 46 chromosomes, a single sperm cell should have a.46 chromosomes. b.23 chromosomes. c.92 chromosomes. d.between 23 and 46 chromosomes.

89. Copyright Pearson Prentice Hall 11-4 During meiosis, the number of chromosomes per cell is cut in half through the separation of a.daughter cells. b.homologous chromosomes. c.gametes. d.chromatids.

90. Copyright Pearson Prentice Hall 11-4 The formation of a tetrad occurs during a.anaphase I. b.metaphase II. c.prophase I. d.prophase II.

91. Copyright Pearson Prentice Hall 11-4 In many female animals, meiosis results in the production of a.only 1 egg. b.1 egg and 3 polar bodies. c.4 eggs. d.1 egg and 2 polar bodies.

92. Copyright Pearson Prentice Hall 11-4 Compared to egg cells formed during meiosis, daughter cells formed during mitosis are a.genetically different, while eggs are genetically identical. b.genetically different, just as egg cells are. c.genetically identical, just as egg cells are. d.genetically identical, while egg cells are genetically different.