1. Observing Patterns in Inherited Traits
Chapter 13
Observing Patterns in Inherited Traits

2. 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. Mendel’s Experiments
Gregor Mendel, an Austrian monk who began breeding thousands of pea plants to document how traits are passed from one generation to the next

4. 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. 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

7. Mendel’s Experiments The experiments
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

8. 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. 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. 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. Inheritance in Modern Terms
Figure 13.3 Genotype gives rise to phenotype. In this example, the dominant allele P , specifies purple flowers; the recessive allele p, white flowers.

12. 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. 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. 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 (F1) offspring will be heterozygous
Genotype = Pp
Phenotype = purple

15. How Are Alleles Distributed Into Gametes?
Punnett square
A grid used to predict the genetic and phenotypic outcome of a cross

16. How Are Alleles Distributed Into Gametes?
female gametes
male gametes
Figure 13.5 Making a Punnett square. Parental gametes are listed in circles on the top and left sides of the grid. Each square is filled with the combination of alleles that would result if the gametes in the corresponding row and column met up.

17. In screech owls, red feathers are dominant over gray feathers
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%

18. In screech owls, red feathers are dominant over gray feathers
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%

19. In canaries, the gene for singing (B) is dominant over the gene for non-singing (b). 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%

20. In canaries, the gene for singing (B) is dominant over the gene for non-singing (b). 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%

21. 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) B) C) D) 200

22. 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) B) C) D) 200

23. 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

24. 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

25. 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

26. 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

27. Phenotype Dominant Recessive Genotype pp P ? or Phenotype All dominant
Figure 9.UN2 Summary: Testcross
All dominant
1 dominant : 1 recessive
Conclusion
Unknown parent
is PP
Unknown parent
is Pp
Figure 9.UN2

28. Two possible genotypes for the black dog:
Testcross
Genotypes B_ bb
Two possible genotypes for the black dog: BB or Bb
Figure 9.10 A Labrador retriever testcross
Gametes B B b b Bb b Bb bb
Offspring
All black
1 black : 1 chocolate
Figure 9.10

29. 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

30. How Are Alleles Distributed Into Gametes?
Table 13.1 Mendel‘s Seven Pea Plant Traits

31. How Are Alleles Distributed Into Gametes?
The probability that second-generation (F2) offspring of (Pp × Pp) will have purple flowers
A ration of 3 purple to 1 white, or 3:1

32. How Are Alleles Distributed Into Gametes?
Law of segregation
The 3:1 phenotype ratios in F2 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

40. In certain rats, black fur is dominant over white fur
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

41. C) three different genotypes and two different colors
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

42. A) 100% Gg B) 50% GG and 50% gg C) 25% GG, 50% Gg, and 25% gg
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

43. A) 100% Gg B) 50% GG and 50% gg C) 25% GG, 50% Gg, and 25% gg
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

44. In a population of dogs, curly hair is dominant over straight hair
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%

45. In a population of dogs, curly hair is dominant over straight hair
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%

46. 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.

47. 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.

48. 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

49. 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

50. 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

51. 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

52. 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

53. 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

54. Which of these crosses will only produce heterozygous offspring?
A) AA × aa
B) AA × Aa
C) Aa × Aa
D) aa × aa
E) Aa × aa

55. Which of these crosses will only produce heterozygous offspring?
A) AA × aa
B) AA × Aa
C) Aa × Aa
D) aa × aa
E) Aa × aa

56. 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

57. A) expresses the dominant trait
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

58. A couple has two female children
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%

59. A couple has two female children
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%

60. 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

61. 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

62. 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%

63. 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%

64. Chromosomes that are not sex chromosomes are called ______.
A) centrosomes
B) allosomes
C) nonsexosomes
D) autosomes
E) dominant

65. Chromosomes that are not sex chromosomes are called ______.
A) centrosomes
B) allosomes
C) nonsexosomes
D) autosomes
E) dominant

66. 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

67. 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