Basic Principles of Heredity Benjamin A. Pierce GENETICS A Conceptual Approach FOURTH EDITION CHAPTER 3 Basic Principles of Heredity © 2012 W. H. Freeman and Company

Chapter 3 Outline 3.1 Gregor Mendel Discovered the Basic Principles of Heredity, 44 3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance, 47 3.3 Dihybrid Crosses Reveal the Principle of Independent Assortment, 56 3.4 Observed Ratios of Progeny May Deviate from Expected Ratios by Chance, 61

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

3.1 Gregor Mendel Discovered the Basic Principles of Heredity Gregor Mendel and his success in genetics Genetic terminology Table 3.1 & Figure 3.2

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.]

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.]

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.]

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.]

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.]

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.]

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. Fig. 3.4

Figure 3.4 Mendel conducted monohybrid crosses.

Figure 3.4 Mendel conducted monohybrid crosses.

Figure 3.4 Mendel conducted monohybrid crosses.

Figure 3.4 Mendel conducted monohybrid crosses.

Figure 3.4 Mendel conducted monohybrid crosses.

Figure 3.4 Mendel conducted monohybrid crosses.

Figure 3.4 Mendel conducted monohybrid crosses.

Figure 3.4 Mendel conducted monohybrid crosses.

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.

3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance Relating Genetic Crosses to Meiosis Chromosome theory of heredity Fig. 3.6 Predicting the outcomes of genetics crosses The Punnett square Fig. 3.7b Probability as a tool in genetics The multiplication rule The addition rule The application of probability to genetics crosses The binomial expansion and probability

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

3.3 Dihybrid Crosses Reveal the Principle of the Independent Assortment The principle of independent assortment Fig. 3.10 Relating the principle of independent assortment to meiosis Applying probability and the branch diagram to dihybrid crosses Fig. 3.11 The Dihybrid testcross Fig. 3.12

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

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

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

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

Figure 3.11 A branch diagram can be sued to determine the phenotypes and expected proportions of offspring from a dihybrid cross (Rr Yy x Rr Yy).

Figure 3.11 A branch diagram can be sued to determine the phenotypes and expected proportions of offspring from a dihybrid cross (Rr Yy x Rr Yy).

Figure 3.11 A branch diagram can be sued to determine the phenotypes and expected proportions of offspring from a dihybrid cross (Rr Yy x Rr Yy).

Figure 3.11 A branch diagram can be sued to determine the phenotypes and expected proportions of offspring from a dihybrid cross (Rr Yy x Rr Yy).

Figure 3.11 A branch diagram can be sued to determine the phenotypes and expected proportions of offspring from a dihybrid cross (Rr Yy x Rr Yy).

Figure 3.11 A branch diagram can be sued to determine the phenotypes and expected proportions of offspring from a dihybrid cross (Rr Yy x Rr Yy).

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

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

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 assorted 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.