Chapter 1313.1 Mendel's Experimental System-What Questions Was Mendel Trying to Answer?oWhat are the basic patterns in the transmission of traits from parents to offspring?-2 hypothesis at the time-Blending inheritance-The traits observed in a mother and father blend together to form the traits in the offspring-Offspring's traits are intermediate between mother's and father's-Inheritance of acquired characters-Traits present in parents are modified through use and passed on to offspring in the modified form-Garden Peas - First Model Organism in GeneticsoMendel could control matings-Pollen grains-Self-fertilization-Cross-fertilizationoMendel studied different traits-Phenotype-Seed shape, seed color, pod shape, pod color, flower color, flower and pod position, and stem length-2 distinct phenotypes existed-Began work with pure lines-Produced hybrids 13.2 Mendel's Experiments with a Single Trait-Monohybrid CrossoA mating between parents that each carry two different determinants for the same traitoCrossed pure lines with just 1 trait-Round seeds with wrinkled seedsoResults-Traits didn't blend together-No intermediate formed-The wrinkled seeds seemed to disappearoSelf-pollinated the F1 seeds-F2 generation results-5474 round; 1850 wrinkled (3:1)-Wrinkled seeds had reappearedoRecessive & Dominant traitsoReciprocal cross-Mendel thought parent gender had an effect-Turned out to be wrong for seed shape-Particulate InheritanceoHereditary determinants maintain their integrity from generation to generation-Instead of blending together, they act like discrete entities or partsoPrinciple of Segregation-To explain 3:1, Mendel thought the 2 members of each gene pair must segregate into different gamete cells during formation of eggs and sperm-Each gamete contains one allele of each geneoHeterozygous & HomozygousoGenetic model-Set of hypotheses that explains how a particular trait is inherited-Dihybrid CrossoA mating between two individuals both heterozygous for two traitsoIndependent assortment-Alleles of different gametes are transmitted independently of one anothero9:3:3:1-TestcrossoA mating between one parent with an unknown genotype with an homozygous recessive other parent 13.4 The Chromosome Theory of Inheritance-Chromosomes are composed of Mendel's hereditary genes-Anaphase of meiosis 1 - principle of segregation-Principle of independent assortment-Chromosome theoryoMendel's rules can be explained by the independent alignment and separation of homologous chromosomes at meiosis I-Sex linkageoX linkage-A gene that resides on the X chromosome-A female has 2 copies of the gene (more chances to be dominant) whereas the male only has 1 copy since his other chromosome is a YoY linkage-A gene that resides on the Y chromosome-Autosomal inheritanceoGenes that are on non-sex chromosomes-X linked inheritanceoConvinced most biologists that the chromosome theory of inheritance was correct 13.5 Extending Mendel's Rules-LinkageoThe physical association between genes on the same chromosomeoException to independent assortment-Crossing OveroOccurs during prophase IoInvolves a physical exchange of segments from homologous chromosomesoOccurs at least once in every homologous pair, usually several timesoLinked genes are inherited together unless crossing over occurs-Incomplete dominanceoHeterozygotes have an intermediate phenotypeoEx: red + white = pink flowers-CodominanceoHeterozygotes show both phenotypesoEx: blood type-Multiple AllelismoMore than two alleles of the same geneoPolymorphic-More than two distinct phenotypes are present in a population due to multiple allelism-PleiotropicoA gene that influences many traits-Ex: Marfan Syndrome geneoA change in a single allele affects more than one trait-Other things that determine phenotypesoPhysical environmentoInteractions between other genes 14.1 What Are Genes Made Of?-Hershey & Chase ExperimentoFound that DNA is the hereditary material, not proteinoDNA contained all the information for life's complexity-Secondary Structure of DNAoWatson & Crick Model-DNA is a long, linear polymer made up of many monomers called deoxyribonucleotides-Consist of a deoxyribose molecule, a phosphate group, and a nitrogenous base-Phosphodiester bonds forms between the hydroxyl group of a 3' carbon of one and the phosphate group on the 5' carbon of another-Primary structure-A sugar-phosphate backbone-A series of nitrogenous basesoA strand of DNA has a polarity-One end has exposed hydroxyl group on the 3' carbon-The other has an exposed phosphate on the 5' carbon-3' end & a 5' endoDouble HelixoAntiparalleloComplementary base pairingoThe existing strands of DNA serve as a template for the production of new strands-Bases are added to the new strands according to complementary base pairing 14.2 The Meselson-Stahl Experiment-3 alternative hypothesis for how the new and old strands of DNA interact during replication1. The old strands separate and each are used as a template-Semiconservative replication-Each new daughter strand consists of one old strand and one new one2. The bases temporarily turn outward so that complementary strands no longer face each other-They could serve as a template for the synthesis of an entirely new double helix all at once-Conservative replication-Results in an intact parental molecule entirely new daughter molecule3. The parent helix is cut in short sections before being unwound, copied, and put back together-New and old segments would alternate-Stretches of old DNA would be interspersed with new DNA down the length of the daughters-Dispersive replication-Their Experiment:1. Wanted to tag/mark parental and daughter strands to make them distinguishable from each other2. Needed to choose an organism to study-E.coli-Because it is small and grows quickly and readily3. Grew the cells in presence of different isotopes of nitrogen-If different N isotopes were available in the growth medium when different generations were produced, then the parental and daughter strands will have different densities-Density gradient centrifugation-Seperates molecules based on their densityoConclusion1. Data from generation 1 conflict with conservative-replication2. Data from generation 2 conflict with dispersive-replication3. Replication is semi-conservative-Each new DNA molecule consists of one old strand and one new strand 14.3 A Comprehensive Model for DNA Synthesis-DNA PolymeraseoPolymerizes deoxyribonucleotides to DNAoFound to catalyze DNA synthesisoCan work in only 1