Chapter 3 Mendelian Genetics Art and Photos in PowerPoint® Concepts of Genetics Ninth Edition Klug, Cummings, Spencer, Palladino Chapter 3 Mendelian Genetics Copyright © 2009 Pearson Education, Inc.

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Figure 3-1 A summary of the seven pairs of contrasting traits and the results of Mendel’s seven monohybrid crosses of the garden pea (Pisum sativum). In each case, pollen derived from plants exhibiting one trait was used to fertilize the ova of plants exhibiting the other trait. In the F1 generation, one of the two traits (dominant) was exhibited by all plants. The contrasting trait (recessive) then reappeared in approximately one-fourth of the F2 plants. Figure 3.1

3.1 Mendel Used a Model Experimental Approach to Study Patterns of Inheritance

3.2 The Monohybrid Cross Reveals How One Trait Is Transmitted from Generation to Generation

Mendel’s First Three Postulates: Pairs of Unit Factors of Inheritance (aka “genes”) Dominance/Recessiveness Principle of Segregation

Figure 3-2 The monohybrid cross between tall and dwarf pea plants Figure 3-2 The monohybrid cross between tall and dwarf pea plants. The symbols D and d designate the tall and dwarf unit factors, respectively, in the genotypes of mature plants and gametes. All individuals are shown in rectangles, and gametes are shown in circles. Figure 3.2

Figure: 03-02a Caption: The monohybrid cross between tall and dwarf pea plants. The symbols D and d designate the tall and dwarf unit factors, respectively, in the genotypes of mature plants and gametes. All individuals are shown in rectangles, and gametes are shown in circles.

Figure: 03-02b Caption: The monohybrid cross between tall and dwarf pea plants. The symbols D and d designate the tall and dwarf unit factors, respectively, in the genotypes of mature plants and gametes. Individuals are shown in rectangles, and gametes in circles.

Figure 3-3 The use of a Punnett square in generating the F2 ratio from the cross shown in Figure 3–2. Figure 3.3

Fig 3-3 Figure: 03-03a Caption: A Punnett square generates the F2 ratio of the F1 x F1 cross shown in Figure 3–2.

Figure: 03-03b Caption: A Punnett square generates the F2 ratio of the F1 x F1 cross shown in Figure 3–2.

How can we determine the genotype of an organism displaying a dominant phenotype?

3.2 The Monohybrid Cross Reveals How One Trait Is Transmitted from Generation to Generation 3.2.5 The Testcross: One Character

Figure 3-4 Testcross of a single character Figure 3-4 Testcross of a single character. In (a), the tall parent is homozygous. In (b), the tall parent is heterozygous. The genotype of each tall parent can be determined by examining the offspring when each is crossed to the homozygous recessive dwarf plant. Figure 3.4

Figure 3-4a Testcross of a single character Figure 3-4a Testcross of a single character. In (a), the tall parent is homozygous. In (b), the tall parent is heterozygous. The genotype of each tall parent can be determined by examining the offspring when each is crossed to the homozygous recessive dwarf plant. Figure 3.4a

Figure 3-4b Testcross of a single character Figure 3-4b Testcross of a single character. In (a), the tall parent is homozygous. In (b), the tall parent is heterozygous. The genotype of each tall parent can be determined by examining the offspring when each is crossed to the homozygous recessive dwarf plant. Figure 3.4b

3.3 Mendel’s Dihybrid Cross Generated a Unique F2 Ratio

Figure 3-5 F1 and F2 results of Mendel’s dihybrid crosses between yellow, round and green, wrinkled pea seeds and between yellow, wrinkled and green, round pea seeds. Figure 3.5

Figure 3-6 Computation of the combined probabilities of each F2 phenotype for two independently inherited characters. The probability of each plant bearing yellow or green seeds is independent of the probability of it bearing round or wrinkled seeds. Figure 3.6

Mendel’s Dihybrid Cross Revealed His Fourth Postulate: Independent Assortment Law of Independent Assortment: During gamete formation, segregating pairs of unit factors assort indepently of each other.

Figure 3-7 Analysis of the dihybrid crosses shown in Figure 3–5 Figure 3-7 Analysis of the dihybrid crosses shown in Figure 3–5. The F1 heterozygous plants are self-fertilized to produce an F2 generation, which is computed using a Punnett square. Both the phenotypic and genotypic F2 ratios are shown. Figure 3.7

Fig 3-7 Figure: 03-07a Caption: Analysis of the dihybrid crosses shown in Figure 3-5. The F1 heterozygous plants are self-fertilized to produce an F2 generation, which is computed using a Punnett square. Both the phenotypic and genotypic F2 ratios are shown.

Fig 3-7 Figure: 03-07b Caption: Analysis of the dihybrid crosses shown in Figure 3–5. The F1 heterozygous plants are self-fertilized to produce an F2 generation, which is computed using a Punnett square. Both the phenotypic and genotypic F2 ratios are shown.

How many phenotypes and genotypes do you expect among the F2 generation?

Fig 3-7 Figure: 03-07c Caption: Analysis of the dihybrid crosses shown in Figure 3–5. The F1 heterozygous plants are self-fertilized to produce an F2 generation, which is computed using a Punnett square. Both the phenotypic and genotypic F2 ratios are shown.

3.3 Mendel’s Dihybrid Cross Generated a Unique F2 Ratio 3.3.2 The Testcross: Two Characters

Figure 3-8 The testcross illustrated with two independent characters.

3.4 The Trihybrid Cross Demonstrates That Mendel’s Principles Apply to Inheritance of Multiple Traits

Figure 3-9 Copyright © 2006 Pearson Prentice Hall, Inc. Trihybrid cross Figure 3-9 Formation of P1 and F1 gametes in a trihybrid cross. ??? Figure 3-9 Copyright © 2006 Pearson Prentice Hall, Inc.

3.4 The Trihybrid Cross Demonstrates That Mendel’s Principles Apply to Inheritance of Multiple Traits 3.4.1 The Forked-Line Method, or Branch Diagram

Figure 3-10 The generation of the F2 trihybrid ratio using the forked-line, or branch diagram method, which is based on the expected probability of occurrence of each phenotype. Figure 3.10

Table 3-1 Simple Mathematical Rules Useful in Working Genetics Problems

3.5 Mendel’s Work Was Rediscovered in the Early Twentieth Century

3.6 The Correlation of Mendel’s Postulates with the Behavior of Chromosomes Provided the Foundation of Modern Transmission Genetics 3.6.1 Unit Factors, Genes, and Homologous Chromosomes

Figure 3-11 The correlation between the Mendelian postulates of (a) unit factors in pairs, (b) segregation, and (c) independent assortment, and the presence of genes located on homologous chromosomes and their behavior during meiosis. Figure 3.11

Figure 3-11a The correlation between the Mendelian postulates of (a) unit factors in pairs, (b) segregation, and (c) independent assortment, and the presence of genes located on homologous chromosomes and their behavior during meiosis. Figure 3.11a

Figure 3-11b The correlation between the Mendelian postulates of (a) unit factors in pairs, (b) segregation, and (c) independent assortment, and the presence of genes located on homologous chromosomes and their behavior during meiosis. Figure 3.11b

Figure 3-11c The correlation between the Mendelian postulates of (a) unit factors in pairs, (b) segregation, and (c) independent assortment, and the presence of genes located on homologous chromosomes and their behavior during meiosis. Figure 3.11c

3.7 Independent Assortment Leads to Extensive Genetic Variation

3.8 Laws of Probability Help to Explain Genetic Events

3.9 Chi-Square Analysis Evaluates the Influence of Chance on Genetic Data 3.9.1 Chi-Square Analysis and the Null Hypothesis

Table 3-3 Chi-Square Analysis

Figure 3-12ab (a) Graph for converting 2 values to p values Figure 3-12ab (a) Graph for converting 2 values to p values. (b) Table of 2 values for selected values of df and p. 2 values greater than those shown at justify failing to reject the null hypothesis, while values less than those at 2 justify rejecting the null hypothesis. In our example, for 1 degree of freedom is converted to a p value between 0.20 and 0.50. The graph in (a) provides an estimated p value of 0.48 by interpolation. In this case, we fail to reject the null hypothesis. Figure 3.12ab

Figure 3-12a (a) Graph for converting 2 values to p values Figure 3-12a (a) Graph for converting 2 values to p values. (b) Table of 2 values for selected values of df and p. 2 values greater than those shown at justify failing to reject the null hypothesis, while values less than those at 2 justify rejecting the null hypothesis. In our example, for 1 degree of freedom is converted to a p value between 0.20 and 0.50. The graph in (a) provides an estimated p value of 0.48 by interpolation. In this case, we fail to reject the null hypothesis. Figure 3.12a

Figure 3-12b (a) Graph for converting 2 values to p values Figure 3-12b (a) Graph for converting 2 values to p values. (b) Table of 2 values for selected values of df and p. 2 values greater than those shown at justify failing to reject the null hypothesis, while values less than those at 2 justify rejecting the null hypothesis. In our example, for 1 degree of freedom is converted to a p value between 0.20 and 0.50. The graph in (a) provides an estimated p value of 0.48 by interpolation. In this case, we fail to reject the null hypothesis. Figure 3.12b

3.10 Pedigrees Reveal Patterns of Inheritance of Human Traits 3.10.1 Pedigree Conventions

Figure 3-13 Conventions commonly encountered in human pedigrees.

3.10 Pedigrees Reveal Patterns of Inheritance of Human Traits 3.10.2 Pedigree Analysis

Figure 3-14a A representative pedigree for an autosomal recessive trait followed through three generations. Figure 3.14a

Figure 3-14b A representative pedigree for an autosomal dominant trait followed through three generations. Figure 3.14b

Chapt 3, Prob 26 Figure: 03-13-03 Caption: In a study of black and white guinea pigs, 100 black animals were crossed individually to white animals and each cross was carried to an F2 generation. In 94 of the cases, the F1 individuals were all black and an F2 ratio of 3 black:1 white was obtained. In the other 6 cases, half of the animals were black and the other half were white. Why? Predict the results of crossing the black and white F1 guinea pigs from the 6 exceptional cases.

Chapt 3, Prob 27 Figure: 03-13-04 Caption: Mendel crossed peas with round green seeds to ones with wrinkled yellow seeds. All F1 plants had seeds that were round and yellow. Predict the results of test crossing these F1 plants.

Chapt 3, Prob 33 Figure: 03-13-05 Caption: Draw all conclusions concerning the mode of inheritance of the trait denoted

Tt Tt TT or Tt tt 2/3 chance Tt 1/2 x 2/3 =1/3 chance Tt 1/3 chance Tt So, chance that child hasTay Sachs (tt)= 1/4 x 1/3 x 1/3 = 1/36

Table 3-4 Representative Recessive and Dominant Human Traits