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Genetics I. I. Mendelian 1. History A. Introduction
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a. C. C. Darwin & A. A. Wallace == blending
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b. In 1860, G. G. Mendel & F. F. Unger == mixing
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1. Monohybrid Cross B. Experimental Design a. Definition
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b. Terms i. Self vs. Cross Fertilization ii. Traits vs. Characteristics
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c. Process
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Figure 10.1 Figure 10.2
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i. Outcomes for a one trait cross or Monohybrid crosses ii. Principle All traits are paired and sorted into gametes Figure 10.3
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d. Terms
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Gene versus Allele Homozygous versus Heterozygous Dominance versus Recessive Genotype versus Phenotype
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e. Testcross
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Figure 10.4
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2. Dihybrid Cross a. Definition b. Process
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Always start these crossing questions by figuring out how many and what type of gametes are produced by the parents. i. Outcomes for a Dihybrid crosses Figure 10.6
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Dihybrid Heterozygous cross = Phenotypic ratio= 9:3:3:1, Genotypic ratio= 1:1:2:2:4:2:2:1:1 Dihybrid Heterozygous cross Homozygous Dominant = Phenotypic ratio = all dominant, Genotypic ratio = 1:1:1:1 ii. Principle Each pair of alleles and chromosomes sort independently into gametes. AaBb X AABB Gametes AaBb = AB, Ab, aB, & ab; AABB= AB only i. Outcomes AaBb X AaBb Gametes AaBb = AB, Ab, aB, & ab for both
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II. II. Variation on Mendel A. Incomplete Dominance
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Incomplete dominance appears to be a blending of the two alleles vs. complete dominant. Figure 10.9
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B. Co-Dominance
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Co-dominance expression of alleles yields both traits in heterozygote. AA aa Aa
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C. Multiple Alleles
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Multiple alleles are needed to give the expression of the trait. Figure 10.10
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D. Penetrance
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Timing of expression of traits in the phenotype.
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1. Pleitrophy E. Gene Interactions
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Pleitrophy one gene = many different effects Figure 10.13
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2. Polygenic
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Polygenic = Continuous Variation of Expression of traits Figure 10.11
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3. Epistasis
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Epistasis = Interference of expression between different genes
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III. III. Classical Genetics A. History
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1. W. W. Bateson & R. R. Punnett (1908) Punnett Square
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2. T. T. Morgan (early 1900’s) used fruit flies WHY? Recombination experiments
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Developed karyotyping techniques, Figure 9.1
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Figure 10.17 linkage group studies, Figure 10.16
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& sex linkage studies Figure 10.15
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3. A. A. Sturtevanta. mapping
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V. V. Detection of Problems
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A. Karyotyping B. Amniocentesis == Cellular and Chemical Analysis
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C. Ultrasound gives a visual image of the fetus D. Chorionic Villi Sampling== placenta samples
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E. Fetal Tissue
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F. Pedigrees == familial history Figure 13.7Figure 13.8
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Figure 13.9
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