1. © Cengage Learning 2015 Biology Concepts and Applications | 9e Starr | Evers | Starr © Cengage Learning 2015 Chapter 13 Observing Patterns in Inherited Traits

2. © Cengage Learning 2015 13.1 How Do Alleles Contribute to Traits? Blending inheritance –19th century idea –Failed to explain how traits disappear over several generations and then reappear unaltered generations later –Charles Darwin did not accept this idea

3. © Cengage Learning 2015 Mendel’s Experiments

4. © Cengage Learning 2015 Mendel’s Experiments Gregor Mendel –Started breeding thousands of pea plants –Kept detailed record of how traits passed from one generation to the next –Began to formulate how inheritance works

5. © Cengage Learning 2015 Mendel’s Experiments Garden pea plant is self-fertilizing –The flowers produce male and female gametes The experiments –Controlled the pairings between individuals with specific traits and observed traits of their offspring –Cross fertilized plants and collected seeds –Recorded traits of new pea plants

6. © Cengage Learning 2015 Mendel’s Experiments The experiments (cont’d.) –Started with garden pea plants that “bred true” for a particular trait – the trait stayed the same generation after generation –Cross-fertilized pea plants with different traits and offspring appeared in predictable patterns –Concluded that hereditary information is passed in discrete units

7. © Cengage Learning 2015 Inheritance in Modern Terms Individuals share certain traits because their chromosomes carry the same genes The DNA sequence of each gene occurs at a specific location The location of a gene on a particular chromosome is called a locus

8. © Cengage Learning 2015 Inheritance in Modern Terms An individual carrying identical alleles for a gene are homozygous An individual carrying two different alleles of a gene is heterozygous Hybrids are heterozygous offspring of a cross between individuals that breed true for different forms of a trait

9. © Cengage Learning 2015 Inheritance in Modern Terms The particular set of alleles that an individual carries is their genotype The observable traits, such as flower color, make up an individual’s phenotype

10. © Cengage Learning 2015 Inheritance in Modern Terms An allele is dominant when its effect masks that of a recessive allele paired with it –A dominant allele is represented by italic capital letters such as (A) –A recessive allele is represented by italic lowercase letters such as (a)

11. © Cengage Learning 2015 Inheritance in Modern Terms

12. © Cengage Learning 2015 13.2 How Are Alleles Distributed Into Gametes? A homozygous pea plant with two alleles (PP) has purple flowers, and one with two alleles (pp) has white flowers If these homozygous plants are crossed (PP × pp), all offspring will be heterozygous

13. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? The allele for purple (P) is dominant over the allele for white (p) Therefore, the heterozygote (Pp) will have purple flowers

14. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? When homozygous dominant and homozygous recessive plants are crossed (PP × pp), only one outcome is possible All first generation (F 1 ) offspring will be heterozygous Genotype = Pp Phenotype = purple

15. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? zygote (Pp) gametes (p) meiosis II gametes (P) DNA replication meiosis I 1 2 3

16. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? Punnett square –A grid used to predict the genetic and phenotypic outcome of a cross

17. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? male gametes female gametes

18. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? Testcross –Breeding experiments used to determine genotype –An individual that has a dominant trait (but an unknown genotype) is crossed with one that is homozygous recessive

19. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? Testcross –If all offspring have dominant trait, than the unknown genotype is homozygous for dominant allele –If any offspring have recessive trait, then it is heterozygous

20. © Cengage Learning 2015 Phenotype P ? Phenotype Genotype Conclusion Recessive Dominant pp All dominant or Unknown parent is PP 1 dominant : 1 recessive Unknown parent is Pp Figure 9.UN2

21. © Cengage Learning 2015 Two possible genotypes for the black dog: B_ bb Testcross Genotypes Bb B b or BB B b Bb bb b Gametes Offspring All black 1 black : 1 chocolate Figure 9.10

22. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? Monohybrid cross –Breeding experiment in which individuals identically heterozygous for one gene are crossed –Frequency of traits among offspring offers information about the dominance relationship between the alleles –First generation = F1 –Second generation = F2

23. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? Mendel investigated seven traits of the pea plants –Stem length (tall and short) –Seed color (yellow and green) –Pod texture (smooth and wrinkled) –Flower color (purple and white) –Flower position (at stem, at tip) –Stem length (tall and short)

24. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes?

25. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? In a monohybrid cross between two Pp plants (Pp × Pp), the two types of gametes can meet in four possible ways: –Sperm P meets egg P → zygote genotype PP –Sperm P meets egg p → zygote genotype Pp –Sperm p meets egg P → zygote genotype Pp –Sperm p meets egg p → zygote genotype pp

26. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? The probability that second-generation (F 2 ) offspring of (Pp × Pp) will have purple flowers –A ration of 3 purple to 1 white, or 3:1

27. © Cengage Learning 2015 How Are Alleles Distributed Into Gametes? Law of segregation –The 3:1 phenotype ratios in F 2 offspring of monohybrid crosses became the basis of Mendel’s law of segregation –Diploid cells carry pairs of genes on each pair of homologous chromosomes. –The two genes of each pair are separated from each other during meiosis so that they end up on different gametes

28. © Cengage Learning 2015 How Are Gene Pairs Distributed Into Gametes? Dihybrid cross –Individuals identically heterozygous for alleles of two genes (dihybrids) are crossed, and the traits of the offspring are observed –Frequency of traits among the offspring offers information about the dominance relationships between the paired alleles

29. © Cengage Learning 2015 How Are Gene Pairs Distributed Into Gametes? One parent plant that breeds true for purple flowers and tall stems (PPTT) is crossed with one that breeds true for white flowers and short stems (pptt) Each plant makes only one type of gamete (PT or pt) All F 1 offspring will be dihybrids (PpTt) and have purple flowers and tall stems

30. © Cengage Learning 2015 How Are Gene Pairs Distributed Into Gametes? The result of two F 1 plants crossing: a dihybrid cross (PpTt × PpTt) Four types of gametes can combine in sixteen possible ways

31. © Cengage Learning 2015 13.4 Are All Genes Inherited in a Mendelian Pattern? Simple dominance – A dominant allele fully masks the expression of a recessive one Other patterns of inheritance are not so simple: –Codominance –Incomplete dominance –Epistasis –Pleiotropy

32. © Cengage Learning 2015 Are All Genes Inherited in a Mendelian Pattern? Codominance –Two alleles that are both fully expressed in heterozygous individuals –Multiple allele systems – gene for which three or more alleles persist in a population –Example: an ABO gene for blood type

33. © Cengage Learning 2015 Are All Genes Inherited in a Mendelian Pattern? Which two of the three alleles of the ABO gene you have determines your blood type –The A and the B allele are codominant when paired Genotype AB = blood type AB –The O allele is recessive when paired with either A or B Genotype AA or AO = blood type A Genotype BB or BO= blood type B Genotype OO = blood type O

34. © Cengage Learning 2015 Are All Genes Inherited in a Mendelian Pattern? Incomplete dominance –One allele is not fully dominant over another –The heterozygous phenotype is between the two homozygous phenotypes

35. © Cengage Learning 2015 Are All Genes Inherited in a Mendelian Pattern? In snapdragons, one allele (R) encodes an enzyme that makes a red pigment, and allele (r) makes no pigment –RR = red; Rr = pink; rr = white A cross between red and white (RR × rr) yields pink (Rr) A cross between two pink (Rr × Rr) yields red, pink, and white in a 1:2:1 ratio

36. © Cengage Learning 2015 In certain rats, black fur is dominant over white fur. If two rats, both heterozygous for fur color, are mated, their offspring would be expected to have? A) four different genotypes and two different colors B) two different genotypes and three different colors C) three different genotypes and two different colors D) three different genotypes and three different colors

37. © Cengage Learning 2015 In certain rats, black fur is dominant over white fur. If two rats, both heterozygous for fur color, are mated, their offspring would be expected to have? A) four different genotypes and two different colors B) two different genotypes and three different colors C) three different genotypes and two different colors D) three different genotypes and three different colors

38. © Cengage Learning 2015 In screech owls, red feathers are dominant over gray feathers. If two heterozygous red- feathered owls are mated, what percentage of their offspring would be expected to have red feathers? A) 25% B) 50% C) 75% D) 100%

39. © Cengage Learning 2015 In screech owls, red feathers are dominant over gray feathers. If two heterozygous red- feathered owls are mated, what percentage of their offspring would be expected to have red feathers? A) 25% B) 50% C) 75% D) 100%

40. © Cengage Learning 2015 In canaries, the gene for singing (S) is dominant over the gene for non-singing (s). When hybrid singing canaries are mated with non-singing canaries, what percentage of the offspring is likely to possess the singing trait? A) 0% B) 25% C) 50% D) 100%

41. © Cengage Learning 2015 In canaries, the gene for singing (S) is dominant over the gene for non-singing (s). When hybrid singing canaries are mated with non-singing canaries, what percentage of the offspring is likely to possess the singing trait? A) 0% B) 25% C) 50% D) 100%

42. © Cengage Learning 2015 The gene for tallness (T) is dominant over the gene for shortness (t) in pea plants. A homozygous dominant pea plant is crossed with a heterozygous pea plant, and 200 seeds are produced. Approximately how many of these seeds can be expected to produce plants that are homozygous dominant? A) 0 B) 50 C) 100 D) 200

43. © Cengage Learning 2015 The gene for tallness (T) is dominant over the gene for shortness (t) in pea plants. A homozygous dominant pea plant is crossed with a heterozygous pea plant, and 200 seeds are produced. Approximately how many of these seeds can be expected to produce plants that are homozygous dominant? A) 0 B) 50 C) 100 D) 200

44. © Cengage Learning 2015 In summer squash, white-colored fruit is dominant over yellow-colored fruit. If homozygous yellow-fruited plants are crossed with heterozygous white-fruited plants, what is the expected percentage of fruit color produced in the offspring? A) 100 % yellow B) 100% white C) 50% yellow, 50% white D) 25% yellow, 75% white

45. © Cengage Learning 2015 In summer squash, white-colored fruit is dominant over yellow-colored fruit. If homozygous yellow-fruited plants are crossed with heterozygous white-fruited plants, what is the expected percentage of fruit color produced in the offspring? A) 100 % yellow B) 100% white C) 50% yellow, 50% white D) 25% yellow, 75% white

46. © Cengage Learning 2015 In a certain species of mouse, gray fur (G) is dominant over cream-colored fur (g). If a homozygous gray mouse is crossed with a cream-colored mouse, the genotype of the F1 generation will most likely be? A) 100% Gg B) 50% GG and 50% gg C) 25% GG, 50% Gg, and 25% gg D) 75% Gg and 25% gg

47. © Cengage Learning 2015 In a certain species of mouse, gray fur (G) is dominant over cream-colored fur (g). If a homozygous gray mouse is crossed with a cream-colored mouse, the genotype of the F1 generation will most likely be? A) 100% Gg B) 50% GG and 50% gg C) 25% GG, 50% Gg, and 25% gg D) 75% Gg and 25% gg

48. © Cengage Learning 2015 In a population of dogs, curly hair is dominant over straight hair. If two parents are heterozygous for this trait, what is the probability that any of their offspring will have straight hair? A) 0% B) 25% C) 75% D) 100%

49. © Cengage Learning 2015 In a population of dogs, curly hair is dominant over straight hair. If two parents are heterozygous for this trait, what is the probability that any of their offspring will have straight hair? A) 0% B) 25% C) 75% D) 100%

50. © Cengage Learning 2015 A true-breeding plant that produces yellow seeds is crossed with a true-breeding plant that produces green seeds. The F1 plants have yellow seeds. What is the expected phenotypic ratio of seed color of the offspring of an F1 × F1 cross? A) 1:2:1 B) 2:1 C) 3:1 D) 9:3:3:1 E) 1:1

51. © Cengage Learning 2015 A true-breeding plant that produces yellow seeds is crossed with a true-breeding plant that produces green seeds. The F1 plants have yellow seeds. What is the expected phenotypic ratio of seed color of the offspring of an F1 × F1 cross? A) 1:2:1 B) 2:1 C) 3:1 D) 9:3:3:1 E) 1:1

52. © Cengage Learning 2015 Alleles are described as ______. A) homologous chromosomes B) environmental factors that affect gene expression C) alternate versions of a gene D) Punnett squares E) alternate phenotypes

53. © Cengage Learning 2015 Alleles are described as ______. A) homologous chromosomes B) environmental factors that affect gene expression C) alternate versions of a gene D) Punnett squares E) alternate phenotypes

54. © Cengage Learning 2015 A true-breeding plant that produces yellow seeds is crossed with a true-breeding plant that produces green seeds. The seeds of all of the offspring are yellow. Why? A) The yellow allele is recessive to the green allele. B) All of the offspring are homozygous yellow. C) The yellow allele is dominant to the green allele. D) The alleles are codominant. E) Yellow is an easier color to produce.

55. © Cengage Learning 2015 A true-breeding plant that produces yellow seeds is crossed with a true-breeding plant that produces green seeds. The seeds of all of the offspring are yellow. Why? A) The yellow allele is recessive to the green allele. B) All of the offspring are homozygous yellow. C) The yellow allele is dominant to the green allele. D) The alleles are codominant. E) Yellow is an easier color to produce.

56. © Cengage Learning 2015 In humans, the presence or absence of dimples is a trait controlled by a single gene. What is the genotype of an individual who is heterozygous for dimples? A) dimples B) DD C) Dd D) dd E) DI

57. © Cengage Learning 2015 In humans, the presence or absence of dimples is a trait controlled by a single gene. What is the genotype of an individual who is heterozygous for dimples? A) dimples B) DD C) Dd D) dd E) DI

58. © Cengage Learning 2015 Which of these crosses will only produce heterozygous offspring? A) AA × aa B) AA × Aa C) Aa × Aa D) aa × aa E) Aa × aa

59. © Cengage Learning 2015 Which of these crosses will only produce heterozygous offspring? A) AA × aa B) AA × Aa C) Aa × Aa D) aa × aa E) Aa × aa

60. © Cengage Learning 2015 To determine the phenotype of an individual who expresses a dominant trait, you would cross that individual with an individual who ______. A) expresses the dominant trait B) is homozygous recessive for that trait C) has the genotype Aa D) is homozygous dominant for that trait E) is heterozygous for that trait

61. © Cengage Learning 2015 To determine the phenotype of an individual who expresses a dominant trait, you would cross that individual with an individual who ______. A) expresses the dominant trait B) is homozygous recessive for that trait C) has the genotype Aa D) is homozygous dominant for that trait E) is heterozygous for that trait

62. © Cengage Learning 2015 A couple has two female children. What is the probability that their next child will be male? A) 25% B) 50% C) 75% D) 33% E) 67%

63. © Cengage Learning 2015 A couple has two female children. What is the probability that their next child will be male? A) 25% B) 50% C) 75% D) 33% E) 67%

64. © Cengage Learning 2015 An individual with (naturally) curly hair and an individual with (naturally) straight hair mate; all of their offspring have (naturally) wavy hair. What is the relationship between the alleles for hair texture? A) pleiotropy B) incomplete dominance C) straight hair and curly hair are sex-linked, but wavy hair is not D) wavy hair is dominant to both straight and curly hair E) codominance

65. © Cengage Learning 2015 An individual with (naturally) curly hair and an individual with (naturally) straight hair mate; all of their offspring have (naturally) wavy hair. What is the relationship between the alleles for hair texture? A) pleiotropy B) incomplete dominance C) straight hair and curly hair are sex-linked, but wavy hair is not D) wavy hair is dominant to both straight and curly hair E) codominance

66. © Cengage Learning 2015 An individual with (naturally) curly hair and an individual with (naturally) straight hair mate; all of their offspring have (naturally) wavy hair. If an individual with wavy hair mates with an individual with straight hair, what is the probability that their child will have curly hair? A) 0% B) 25% C) 50% D) 75% E) 100%

67. © Cengage Learning 2015 An individual with (naturally) curly hair and an individual with (naturally) straight hair mate; all of their offspring have (naturally) wavy hair. If an individual with wavy hair mates with an individual with straight hair, what is the probability that their child will have curly hair? A) 0% B) 25% C) 50% D) 75% E) 100%

68. © Cengage Learning 2015 Chromosomes that are not sex chromosomes are called ______. A) centrosomes B) allosomes C) nonsexosomes D) autosomes E) dominant

69. © Cengage Learning 2015 Chromosomes that are not sex chromosomes are called ______. A) centrosomes B) allosomes C) nonsexosomes D) autosomes E) dominant

70. © Cengage Learning 2015 The parents of a child with unusual disease symptoms take the child to a doctor for help. The doctor suspects that the condition might have a genetic basis. She recommends that the child be taken to a specialty clinic where physicians and staff members are trained to diagnose genetic diseases and counsel parents. Ultimately, the child is diagnosed with a rare recessively inherited disease. The parents are tested for the gene, and both are found to be heterozygous. The parents want to have another child but are afraid this child will also be affected. What would genetic counselors say is the probability that the second child will have the disease? A) 1/2 B) 1/4 C) 1/8 D) 1/16 E) 1/32

71. © Cengage Learning 2015 The parents of a child with unusual disease symptoms take the child to a doctor for help. The doctor suspects that the condition might have a genetic basis. She recommends that the child be taken to a specialty clinic where physicians and staff members are trained to diagnose genetic diseases and counsel parents. Ultimately, the child is diagnosed with a rare recessively inherited disease. The parents are tested for the gene, and both are found to be heterozygous. The parents want to have another child but are afraid this child will also be affected. What would genetic counselors say is the probability that the second child will have the disease? A) 1/2 B) 1/4 C) 1/8 D) 1/16 E) 1/32

72. © Cengage Learning 2015 10/8 Protein Synthesis 910/10 Genes 10 10/15 Mitosis 1110/17 Meiosis 12 10/22 Genotype & Phenotype 1310/24 Biotechnology 14 10/29 Exam #2 10/31 Begin Evolution