1. Basic Principles of Heredity
Benjamin A. Pierce
GENETICS
A Conceptual Approach
FIFTH EDITION
CHAPTER 3
Basic Principles of Heredity
© 2014 W. H. Freeman and Company

2. Red hair is caused by recessive mutations at the melanocortin 1 receptor gene. Reed Kaestner/Corbis

3. 3.1 Gregor Mendel Discovered the Basic Principles of Heredity
Gregor Mendel and his success in genetics
Proper experimental model
Used an experimental approach and analyzed results mathematically
Studied easily differentiated characteristics

4. Figure 3.2 Mendel used the pea plant Pisum sativum in his studies of heredity. He examined seven characteristics that appeared in the seeds and in plants grown from the seeds. [Photograph by Wally Eberhart/Visuals Unlimited.]

6. 3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance
Monohybrid cross: cross between two parents that differ in a single characteristic.
Conclusion 1: one character is encoded by two genetic factors.
Conclusion 2: two genetic factors (alleles) separate when gametes are formed.
Conclusion 3: The concept of dominant and recessive traits.
Conclusion 4: Two alleles separate with equal probability into the gametes.

7. Figure 3.4 Mendel conducted monohybrid crosses.

8. Figure 3.4 Mendel conducted monohybrid crosses.

9. Figure 3.4 Mendel conducted monohybrid crosses.

10. Figure 3.4 Mendel conducted monohybrid crosses.

11. Figure 3.4 Mendel conducted monohybrid crosses.

12. Figure 3.4 Mendel conducted monohybrid crosses.

13. 3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance
Principle of segregation: (Mendel’s first law)
Each individual diploid organism possesses two alleles for any particular characteristic. These two alleles segregate when gametes are formed, and one allele goes into each gamete.
The concept of dominance: when two different alleles are present in a genotype, only the trait encoded by one of them―the “dominant” allele―is observed in the phenotype.

14. 3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance
Monohybrid crosses explained by the principle of segregation
The symbols in genetic crosses correspond to alleles on chromosomes
Sutton: Chromosomal Theory of Heredity

15. Figure 3.6 Segregation results from the separation of homologous chromosomes in meiosis.

16. Figure 3.6 Segregation results from the separation of homologous chromosomes in meiosis.

17. Figure 3.6 Segregation results from the separation of homologous chromosomes in meiosis.

18. Figure 3.6 Segregation results from the separation of homologous chromosomes in meiosis.

19. Figure 3.6 Segregation results from the separation of homologous chromosomes in meiosis.

20. Figure 3.6 Segregation results from the separation of homologous chromosomes in meiosis.

21. Figure 3.6 Segregation results from the separation of homologous chromosomes in meiosis.

22. Figure 3.6 Segregation results from the separation of homologous chromosomes in meiosis.

23. Figure 3.6 Segregation results from the separation of homologous chromosomes in meiosis.

24. Figure 3.6 Segregation results from the separation of homologous chromosomes in meiosis.

25. 3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance
Tested the theory of inheritance of dominant traits using backcrosses
Predicting the outcomes of genetics crosses
The Punnett square
Figure 3.7b

26. Figure 3.7 The Punnett square can be used to determine the results of a genetic cross.

27. Figure 3.7 The Punnett square can be used to determine the results of a genetic cross.

28. Figure 3.7 The Punnett square can be used to determine the results of a genetic cross.

29. Concept Check 1
If an F1 plant depicted in Figure 3.4 is backcrossed to the parent with round seeds, what proportion of the progeny will have wrinkled seeds? (Use a Punnett square.)
a. ¾
b. ½
c. ¼
d. 0

30. Concept Check 1
If an F1 plant depicted in Figure 3.4 is backcrossed to the parent with round seeds, what proportion of the progeny will have winkled seeds? (Use a Punnett square.)
a. ¾
b. ½
c. ¼
d. 0

31. Probability
Probability: the likelihood of the occurrence of a particular event
Used in genetics to predict the outcome of a genetic cross
Multiplication rule
Addition rule

32. Figure 3.8 The multiplication and addition rules can be used to determine the probability of a combination of events.

33. Figure 3.8 The multiplication and addition rules can be used to determine the probability of a combination of events.

34. Figure 3.8 The multiplication and addition rules can be used to determine the probability of a combination of events.

35. Figure 3.8 The multiplication and addition rules can be used to determine the probability of a combination of events.

36. Concept Check 2
If the probability of being blood-type A is 1/8 and the probability of blood-type O is ½, what is the probability of being either blood-type A or O?
a. 5/8
b. ½
c. 1/8
d. 1/16

37. Concept Check 2
If the probability of being blood-type A is 1/8 and the probability of blood-type O is ½, what is the probability of being either blood-type A or O?
a. 5/8
b. ½
c. 1/8
d. 1/16

38. Ratios in Simple Crosses
3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance
The Testcross
- Figure 3.7
Ratios in Simple Crosses
Tables 3.3 & 3.4

41. 3.3 Dihybrid Crosses Reveal the Principle of Independent Assortment
Examine two traits at a time
The principle of independent assortment
Figure 3.10

42. Figure 3.10 Mendel’s dihybrid crosses revealed the principle of independent assortment.

43. Figure 3.10 Mendel’s dihybrid crosses revealed the principle of independent assortment.

44. Figure 3.10 Mendel’s dihybrid crosses revealed the principle of independent assortment.

45. Figure 3.10 Mendel’s dihybrid crosses revealed the principle of independent assortment.

46. 3.3 Dihybrid Crosses Reveal the Principle of Independent Assortment
Relate the principle of independent assortment to meiosis
Gametes located on different chromosomes will sort independently

48. 3.3 Dihybrid Crosses Reveal the Principle of Independent Assortment
Applying probability and the branch diagram to dihybrid crosses
Figure 3.11

52. Figure 3.12 A branch diagram can be used to determine the phenotypes and expected proportions of offspring from a dihybrid testcross (Rr Yy  Rr Yy).

53. 3.4 Observed Ratios of Progeny May Deviate from Expected Ratios by Chance
- Chi-Square Goodness of Fit
- Indicates the probability that the difference between the observed and expected values is due to chance

58. Concept Check 3
How are the principles of segregation and independent assortment related and how are they different?

59. Concept Check 3
How are the principles of segregation and independent assortment related and how are they different?
Answer:
Genes encoding different characteristics separate and assort independently of one another when they do not locate close together on the same chromosome.
During this process, two alleles of the same gene encoding one characteristic still have to be segregated from each other during the formation of gametes.