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Go to Section: The Father of Genetics – Gregor Johann Mendel (1822-1884) 1863 - 1866 Mendel cultivated and tested some 28 000 pea plants Go to Section: Allele – Different form of a gene Dominant allele - In a heterozygote, the allele that is fully expressed in the phenotype. Recessive allele - In a heterozygote, the allele that is completely masked in the phenotype. Phenotype – The outward appearance of a trait Genotype – The combination of alleles (Letters) Go to Section: Mendel’s Experiments •Used 34 "true-breeding" strains of the common garden pea plant •These strains differed from each other in very pronounced (visible) ways so that there could be no doubt as the results of a given experiment. •Pea plants were perfect for such experiments since their flowers had both male (anthers) and female (pistils) flower parts •The flower petals never open therefore no foreign pollen could enter and back crosses (self fertilization) was easy. Go to Section: Go to Section: Flower Parts Go to Section: Principles of Dominance Section 11-1 P Generation Tall Go to Section: Short F1 Generation Tall Tall F2 Generation Tall Tall Tall Short Principles of Dominance Section 11-1 P Generation Tall Go to Section: Short F1 Generation Tall Tall F2 Generation Tall Tall Tall Short Principles of Dominance Section 11-1 P Generation Tall Go to Section: Short F1 Generation Tall Tall F2 Generation Tall Tall Tall Short Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Section 11-1 Seed Coat Color Pod Shape Pod Color Smooth Green Seed Shape Seed Color Round Yellow Gray Wrinkled Green White Constricted Round Yellow Gray Smooth Go to Section: Flower Position Plant Height Axial Tall Yellow Terminal Short Green Axial Tall Section Outline Section 11-2 11–2 Probability and Punnett Squares A. B. C. D. Go to Section: Genetics and Probability Punnett Squares Probability and Segregation Probabilities Predict Averages Tt X Tt Monohybrid Cross Section 11-2 Go to Section: Tt X Tt Cross Section 11-2 Go to Section: Monohybrid Cross Phenotypes Go to Section: Law of Segregation Go to Section: Section Outline Section 11-3 11–3 Exploring Mendelian Genetics A. Independent Assortment 1. The Two-Factor Cross: F1 2. The Two-Factor Cross: F2 B. A Summary of Mendel’s Principles C. Beyond Dominant and Recessive Alleles 1. Incomplete Dominance 2. Codominance 3. Multiple Alleles 4. Polygenic Traits D. Applying Mendel’s Principles E. Genetics and the Environment Go to Section: Concept Map Section 11-3 Gregor Mendel concluded that experimented with Pea plants Go to Section: “Factors” determine traits Some alleles dominant, & some alleles recessive Alleles are separated during gamete formation which is called the which is called the Law of Dominance Law of Segregation Figure 11-10 Independent Assortment in Peas Section 11-3 Go to Section: Dihybrid Cross Section 11-2 Go to Section: Figure 11-11 Incomplete Dominance in Four O’Clock Flowers Section 11-3 Go to Section: Figure 11-11 Incomplete Dominance in Four O’Clock Flowers Section 11-3 Go to Section: Section Outline Section 11-4 11–4 Meiosis A. Chromosome Number B. Phases of Meiosis 1. Meiosis I 2. Meiosis II C. Gamete Formation D. Comparing Mitosis and Meiosis Go to Section: Homologous Chromosome Go to Section: Crossing-Over Section 11-4 Go to Section: Crossing-Over Section 11-4 Go to Section: Crossing-Over Section 11-4 Go to Section: Go to Section: Figure 11-15 Meiosis Section 11-4 Meiosis I Go to Section: Figure 11-15 Meiosis Section 11-4 Meiosis I Go to Section: Figure 11-15 Meiosis Section 11-4 Meiosis I Go to Section: Figure 11-15 Meiosis Section 11-4 Meiosis I Go to Section: Figure 11-15 Meiosis Section 11-4 Meiosis I Go to Section: Figure 11-17 Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Go to Section: Telophase II Meiosis II results in four haploid (N) daughter cells. Figure 11-17 Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Go to Section: Telophase II Meiosis II results in four haploid (N) daughter cells. Figure 11-17 Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Go to Section: Telophase II Meiosis II results in four haploid (N) daughter cells. Figure 11-17 Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Go to Section: Telophase II Meiosis II results in four haploid (N) daughter cells. Figure 11-17 Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Go to Section: Telophase II Meiosis II results in four haploid (N) daughter cells. Genetic Recombination Go to Section: Interest Grabber Section 11-5 Forever Linked? Some genes appear to be inherited together, or “linked.” If two genes are found on the same chromosome, does it mean they are linked forever? Study the diagram, which shows four genes labeled A–E and a–e, and then answer the questions on the next slide. Go to Section: Interest Grabber continued Section 11-5 1. In how many places can crossing over result in genes A and b being on the same chromosome? 2. In how many places can crossing over result in genes A and c being on the same chromosome? Genes A and e? 3. How does the distance between two genes on a chromosome affect the chances that crossing over will recombine those genes? Go to Section: Section Outline Section 11-5 11–5 Linkage and Gene Maps A. Gene Linkage B. Gene Maps Go to Section: Comparative Scale of a Gene Map Section 11-5 Mapping of Earth’s Features Mapping of Cells, Chromosomes, and Genes Cell Earth Country Chromosome State Chromosome fragment City People Go to Section: Gene Nucleotide base pairs Figure 11-19 Gene Map of the Fruit Fly Section 11-5 Exact location on chromosomes Go to Section: Chromosome 2 Video 1 Meiosis Overview Click the image to play the video segment. Video 2 Animal Cell Meiosis, Part 1 Click the image to play the video segment. Video 3 Animal Cell Meiosis, Part 2 Click the image to play the video segment. Video 4 Segregation of Chromosomes Click the image to play the video segment. Video 5 Crossing Over Click the image to play the video segment. Interest Grabber Answers 1. In how many places can crossing over result in genes A and b being on the same chromosome? One (between A and B) 2. In how many places can crossing over result in genes A and c being on the same chromosome? Genes A and e? Two (between A and B and A and C); Four (between A and B, A and C, A and D, and A and E) 3. How does the distance between two genes on a chromosome affect the chances that crossing over will recombine those genes? The farther apart the genes are, the more likely they are to be recombined through crossing over.