chapter 3 notes

chapter 3 notes - Chapter 3 "Mendelian Genetics"...

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Chapter 3 “Mendelian Genetics” Inherited characteristics are under the control of discrete particulate factors called genes that are transmitted from generation to generation on vehicles called chromosomes, according to rules first described by Gregor Johann Mendel. The outcomes of these rules are affected by chance deviation and can be evaluated using statistical analysis. Human traits are initially studied using the pedigree method. “Mendelian Genetics” 3.1 Gregor Johann Mendel 39 3.2 Monohybrid cross 39-43 3.3 Dihybrid cross 43-46 3.4 Trihybrid cross 46-47 3.5 Rediscovery of Mendel’s work 47-49 3.6 Independent assortment 49 3.7 Probability and genetic events 49-50 3.8 Evaluating genetic data-Chi square 50-52 P. 55 Tay-Sachs Disease 3.1 Gregor Johann Mendel Some highlights of Mendel’s life -He is considered the “Father of transmission genetics” -Born in 1822 to a peasant family in Heinzeldorf (Czech Republic). -Admitted to the Augustinian Monastery of St. Thomas in the Czech Republic -From 1851 to 1853 he studied physics and botany at the University of Vienna -He taught physics and natural sciences for the next 16 years -Began his hybridization of garden pea in 1856, -Terminated his experiments in 1868 when he was elected Abbot -First reported his results in 1865, but they went unnoticed until early in the 20 th Century -He died in 1884 of kidney failure. Why did Mendel succeed where others failed? 1. He chose the correct organism, the garden pea. Easy to grow and hybridize (large floral parts). Has a fairly short life cycle. Morphological traits are easily distinguished. See Figure 3-1 2. Chose traits that were controlled by single dominant genes. Flower color, seed texture, etc. He restricted his studies to these traits.
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3. Each trait was inherited independently. We will discuss this concept in Ch 7. See p. 157 4. He kept accurate and quantitative records. This allowed his hypotheses about ratios to be formulated. This was likely the most important reason that Mendel succeeded. Mendel in Modern Terms -Mendel did not coin the term “gene” -Mendel referred to “unit factors” for different forms of a gene (alleles) Gene = the unit of inheritance Allele= alternate forms of a gene 3.2 The Monohybrid Cross Monohybrid cross = Mono (one trait) hybrid (a cross between two dissimilar parents) Example Tall vs short pea plants controlled by a single gene Phenotypes: Tall vs Short This is Mendel’s First Postulate of Inheritance = Unit factors occur in pairs See Figure 3.2 Calculation of expected phenotypic frequencies based on frequency of gametes produced by parental genotypes Punnett Square An easy way to determine the expected phenotypic frequencies See Figure 3-3 Mendel’s First Three Postulates 1. Unit factors (alleles) occur in pairs Three combinations of alleles are possible at one loci in a diploid organism
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This note was uploaded on 02/20/2008 for the course SORC 330 taught by Professor Brick during the Spring '08 term at Colorado State.

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chapter 3 notes - Chapter 3 "Mendelian Genetics"...

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