2 Chapter 3 Outline3.1 Gregor Mendel Discovered the Basic Principles of Heredity, 443.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance, 473.3 Dihybrid Crosses Reveal the Principle of Independent Assortment, 553.4 Observed Ratios of Progeny May Deviate from Expected Ratios by Chance, 60
3 The Case of the Red Hair Did you read the Chapter 3? What do you think, what is the case?Did you find any new research on the subject?Are you ready to present?Red hair is caused by recessive mutations at the melanocortin 1 receptor gene. Reed Kaestner/Corbis
4 Mendel and His Study of Heredity His success was result of his choice of model organism Pisum sativumRapid growthMany offspringLarge number of varieties with known genetic makeup7 characteristics he investigatedAnd his mathematical knowledge
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.Fig. 3.3
7 Experimental OutlineMendel used this approach for all studied characteristicsObserveCountAnalyze
8 The Monohybrid CrossConclusion 1: one character is encoded by two genetic factors.Cross between parents different in a single characteristic (in this example seed shape; round or wrinkled)Parental (P) generationPure breed (homozygous)Filial 1 (F1) generationUniform only one characteristicFilial 2 (F2) generationBoth characteristics appear in 3:1 ratio
9 b. Both parental phenotypes reappeared in the F2 generation. In Mendel’s pea plants, how did he know that each F1 generation contained two alleles encoding different characteristics?a. The F1 generation had a blended phenotype of the two parental phenotypes.b. Both parental phenotypes reappeared in the F2 generation.c. Each F1 plant had a different phenotype.d. The F1 plants did not have two alleles.e. None of the above.Location: 3.2 Monohybrid Crosses Reveal the Principle of Segregation and the Concept of DominanceWhat Monohybrid Crosses RevealConcept Check 3
10 The Labeling of Factors (Alleles) Conclusion 3: The concept of dominant and recessive traits. Remember meiosis and gamete formation?Each gamete and representative allele is labeled with a letter that corresponds to the characteristic studiedR for round (dominant)r for wrinkled (recessive)
11 The Factors (Alleles) in the Experiment Conclusion 2: two genetic factors (alleles) separate when gametes are formed.What happens with the alleles in the cross of the P generation?F1 generation is heterozygous RrF1 generation form gametesEach plant two different gametes
12 The Alleles in the Next Generation Conclusion 4: Two alleles separate with equal probability into the gametes.Self fertilization of F1 plantsThe two gametes combine and fertilize randomlyF2 generationTwo phenotypes (3:1 ratio)Three genotypesRRRrrrHow will that be determined?
14 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.
15 The Crosses and the Meiosis Introduction to chromosome theory of heredity
18 Predicting the Outcomes of Genetic Crosses- The Punnett Square The example of backcross on tall and short plants (T and t alleles)F1 heterozygous (Tt) plant with homozygous recessive (tt) parental varietyGenerate possible gametes from each parentAlign the gametes from one parent vertically on the leftAlight the gametes of the other parent horizontally on topMIX and count
19 Predicting the Outcomes of Genetic Crosses- Multiplication Rule Two or more independent events taking place togetherKey word is andProbability to roll 4 is 1/6What is the probability to obtain 4 in the first and the second try?1/6 in the first and 1/6 in the second1/6 X 1/6 = 1/36Independent means that the first does not influence the second
22 3.3 Dihybrid Crosses Reveal the Principle of the Independent Assortment The principle of independent assortmentRelating the principle of independent assortment to meiosisApplying probability and the branch diagram to dihybrid crossesThe Dihybrid testcross
23 Dihybrid CrossCross between parents different in two characteristic (in this example seed shape and color; round/wrinkled and yellow/green)Parental (P) generationPure breed (homozygous for two characteristics)Filial 1 (F1) generationUniform round/yellowFilial 2 (F2) generationVarious combinations of the two characteristics appear in 9:3:3:1 ratio
24 The Factors (Alleles) in the Experiment Conclusion: genetic factors (alleles) of the first trait separate independently from the alleles of the second traitWhat happens with the alleles in the cross of the P generation?F1 generation is heterozygous for both traits RrYyF1 generation form gametesEach sex forms four differentgametes
25 The Alleles in the Next Generation Conclusion: genetic factors (alleles) of the first trait separate independently from the alleles of the second traitSelf fertilization of F1 plantsThe four gametes fertilize randomlyF2 generationFour phenotypes16 genotypes in 9:3:3:1 ratio
26 The Meiotic Behavior of Chromosomes Explains the Independent Assortment
27 Crosses and Probabilities- Branched Diagrams-Monohybrid
28 Crosses and Probabilities- Branched Diagrams-Dihybrid
29 Crosses and Probabilities- Branched Diagrams-Dihybrid Test Cross ½ Yy½ yy¼ Rr Yy¼ Rr yy¼ rr Yy¼ rr yy½ Rr½ rr½ Yy½ yy
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