Genetics: A Conceptual Approach 7th Edition Lecture Slides - Chapter 3 PDF

Benjamin A. Pierce Genetic s A Conceptual Approach SEVENTH EDITION Lecture Slides CHAPTER 3 Basic Principles of Heredity Copyright © 2020, W.H. Freeman and Company The Genetics of Blond Hair in the South Pacific Mendel’s Success  3.1 G...

Benjamin A. Pierce Genetic s A Conceptual Approach SEVENTH EDITION Lecture Slides CHAPTER 3 Basic Principles of Heredity Copyright © 2020, W.H. Freeman and Company The Genetics of Blond Hair in the South Pacific Mendel’s Success  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 Pisum Sativum  Concept Check 1 (1 of 2) Which of the following factors did not contribute to Mendel’s success in his study of heredity? a. his use of the pea plant b. his study of plant chromosomes c. his adoption of an experimental approach d. his use of mathematics  Concept Check 1 (2 of 2) Which of the following factors did not contribute to Mendel’s success in his study of heredity? a. his use of the pea plant b. his study of plant chromosomes c. his adoption of an experimental approach d. his use of mathematics  TABLE 3.1 Summary of important genetic terms Term Definition Gene An inherited factor (encoded in the DNA) that helps determine a characteristic Allele One of two or more alternative forms of a gene Locus Specific place on a chromosome occupied by an allele Genotype Set of alleles possessed by an individual organism Heterozygote An individual organism possessing two different alleles at a locus Homozygote An individual organism possessing two of the same alleles at a locus Phenotype or trait The appearance or manifestation of a characteristic Characteristic or character An attribute or feature possessed by an organism Genetic Terminology  Concept Check 2 (1 of 2) What is the difference between a locus and an allele? What is the difference between genotype and phenotype?  Concept Check 2 (2 of 2) What is the difference between a locus and an allele? What is the difference between genotype and phenotype? A locus is a place on a chromosome where genetic information encoding a characteristic is located. An allele is a version of a gene that encodes a specific trait. A genotype is the set of alleles possessed by an individual organism. A phenotype is the manifestation or appearance of a characteristic.  3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance (1 of 5) 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. An Experiment  3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance (2 of 5) 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 (3 of 5) Monohybrid crosses are explained by the principle of segregation. The symbols in genetic crosses correspond to alleles on chromosomes. Sutton: chromosomal theory of heredity What Monohybrid Crosses Reveal  TABLE 3.2 Comparison of the principles of segregation and independent assortment Principle Observation State of Meiosis* Segregation (Mendel’s first law) 1. Each individual organism Before meiosis possesses two alleles encoding a trait. 2. Alleles separate when Anaphase I gametes are formed. 3. Alleles separate in Anaphase I equal proportions. Independent assortment Alleles at different loci Anaphase I (Mendel’s second law) separate independently. *Assumes that no crossing over occurs. If crossing over takes place, then segregation and independent assortment may also occur in anaphase II of meiosis.  Concept Check 3 (1 of 2) How did Mendel know that each of his pea plants carried two alleles encoding a characteristic?  Concept Check 3 (2 of 2) How did Mendel know that each of his pea plants carried two alleles encoding a characteristic? The traits encoded by both alleles appeared in the F2 progeny. Segregation Results from the Separation of the Homologous Chromosomes in Meiosis  3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance (4 of 5) Tested the theory of inheritance of dominant traits using backcrosses Predicted the outcomes of genetic crosses – The Punnett square – Figure 3.8 The Punnett Square  Concept Check 4 (1 of 2) If an F1 plant depicted in Figure 3.6 is backcrossed to the parent with round seeds, what proportion of the progeny will have winkled seeds? (Use a Punnett square.) a. 3/4 b. 1/2 c. 1/4 d. 0  Concept Check 4 (2 of 2) If an F1 plant depicted in Figure 3.6 is backcrossed to the parent with round seeds, what proportion of the progeny will have winkled seeds? (Use a Punnett square.) a. 3/4 b. 1/2 c. 1/4 d. 0  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 The Multiplication Rule The Addition Rule  Concept Check 5 (1 of 2) If the probability of being blood-type A is 1/8 and the probability of blood-type O is 1/2, what is the probability of being either blood-type A or O? a. 5/8 b. 1/2 c. 1/8 d. 1/16  Concept Check 5 (2 of 2) If the probability of being blood-type A is 1/8 and the probability of blood-type O is 1/2, what is the probability of being either blood-type A or O? a. 5/8 b. 1/2 c. 1/8 d. 1/16  Binomial Expansion Useful for complex situations Binomial takes the form (p + q)n – p equals the probability of one event – q equals the probability of the alternative event – n equals the number of times the event occurs – Tables 3.3 and 3.4  TABLE 3.3 Pascal's triangle The numbers in each row represent the coefficients of each term in the binomial expansion (p + q)n. n Coefficients 1 1 11 2 121 3 1331 4 14641 5 1 5 10 10 5 1 6 1 6 15 20 15 6 1  TABLE 3.4 Coefficients and terms for the binomial expansion (p + q)n for n = 1 through 5 n Binomial Expansion 1 a+b 2 a2 + 2ab + b2 3 a3 + 3a2b + 3ab2 + b3 4 a4 + 4a3b + 6a2b2 + 4ab3 + b4 5 a5 + 5a4b + 10a3b2 + 10a2b3 + 5ab4 + b5  3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance (5 of 5) The testcross – Figure 3.8 Ratios in simple crosses – Tables 3.5 and 3.6 TABLE 3.5 Phenotypic ratios for simple genetic crosses (crosses for a single locus) with dominance Phelotypic Ratio Genotypes of Parents Genotypes of Progeny 3:1 Aa × Aa 3 /4 A_ : 1/4 aa 1:1 Aa × aa 1 /2 Aa : 1/2 aa AA × AA All AA aa × aa All aa Uniform progeny AA × aa All Aa AA × Aa All A_ TABLE 3.6 Genotypic ratios for simple genetic crosses (crosses for a single locus Genotypic Ratio Genotypes of Parents Genotypes of Progeny 1:2:1 Aa × Aa 1 /4 AA : 1/2 Aa : 1/4 aa Aa × aa 1 /2 Aa : 1/2 aa 1:1 AA × AA 1 /2 Aa : 1/2 AA AA × AA All AA Uniform progeny aa × aa All aa AA × aa All Aa 3.3 Dihybrid Crosses Reveal the Principle of Independent Assortment (1 of 2) Dihybrid crosses – Examine two traits at a time – The principle of independent assortment Figure 3.11 Mendel’s Dihybrid Crosses 3.3 Dihybrid Crosses Reveal the Principle of Independent Assortment (2 of 2) Dihybrid crosses – Relate the principle of independent assortment to meiosis – Gametes located on different chromosomes will sort independently Relating the Principle of Independent Assortment to Meiosis  Concept Check 6 (1 of 2) How are the principles of segregation and independent assortment related, and how are they different?  Concept Check 6 (2 of 2) How are the principles of segregation and independent assortment related, and how are they different? Both the principle of segregation and the principle of independent assortment refer to the separation of alleles in anaphase I of meiosis. – The principle of segregation says that these alleles separate. – The principle of independent assortment says that they separate independently of alleles at other loci.  3.3 Dihybrid Crosses Reveal the Principle of Independent Assortment Dihybrid crosses – Applying probability and the branch diagram to dihybrid crosses Figure 3.13 Applying Probability and the Branch Diagram to Dihybrid Crosses The Dihybrid Testcross  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 A Chi-Square Goodness-of-Fit Test  Concept Check 7 (1 of 2) A chi-square test comparing observed and expected numbers of progeny is carried out, and the probability associated with the calculated chi- square value is 0.72. What does this probability represent? a. probability that the correct results were obtained b. probability of obtaining the observed numbers c. probability that the difference between observed and expected numbers is significant d. probability that the difference between observed and expected numbers could be due to chance  Concept Check 7 (2 of 2) A chi-square test comparing observed and expected numbers of progeny is carried out, and the probability associated with the calculated chi- square value is 0.72. What does this probability represent? a. probability that the correct results were obtained b. probability of obtaining the observed numbers c. probability that the difference between observed and expected numbers is significant d. probability that the difference between observed and expected numbers could be due to chance