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Chapter 1

Chapter 1: Genetic Approach to Biology Summary of Chapter 1 (Intro to Genetics 5ed Alberts) 1. History 2. Model Organisms 3. Influences over genotype and phenotype expression 4. Transcription and Translation 5. genetic Analysis (forward and reverse

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BIOL 2040
Joel Shore

08/01/11 Chapter 1: Genetic approach to Biology - All life begins as a single cell that is fertilized by an egg and sperm - All multicellular cells undergo fertilization of a zygote  adult - When cells divide, they produce new cells that are physically and chemically different thus have different functions o i.e. blood cells, secretory cells, nerve cells, etc. - biological properties of an organism is defined at the end of the developmental stages and the traits are passed on from the parents o Traits have 4 mandatory properties: 1. diversity of structure  the cells that carries information for a function or the development of organisms comes in various shapes and forms 2. ability to replicate  reproductive mechanism that allows for copying of information so it can be inherited from parent to offspring 3. mutability  information can go through mutations that result in different morphological traits  larger numbers of mutations that accumulate can result in the formation of completely new structures 4. Translations  Events of translation is to occur in order to read out the gene - Gene: inherited information - Genome: collection of genes - Genetics: study of diversity, replications, mutations, translation (the 4 properties above) Genetics and the Question of Biology th - 15 c. Gregor Mendel was the first to discover genetics o Studied pea garden and noted that there were “factors” that were inheritable from parent to offspring - 20 c. information specifying development was contained in the chromos in nucleus - Crosses between differing variants which are inheritable correspond to chromo distribution into gametes at meiosis - Genes on chromo are responsible for information of characters o Affects every aspect of structure and function of an organism Genetic analysis - Genetic Analysis: using organisms with mutations for investigating developmental, physiological and biochemical pathways that make up an organism - X-rays, chemicals, deletion and duplication cause mutations - effects visible through morphology - i.e. Study of fruit flies, Drosophila, that undergone mutations determined that variation in mutations gives rise to evolution - 1920s, DNA is the genetic material o DNA is found in genes (Figure 1-2) o DNA replication, mutation and information processing is continuous process in an organism’s life (Figure 1-4) - Genetics is the basis of evolutionary change: different rates of reproduction of individuals with different inheritable traits - DNA sequencing allows for determination of divergence in different parts of the genome The Molecular Basis of Genetic Information - Proteins: controls the structures of organisms and physiological process - DNA: genetic information that allows for the synthesis of proteins o Structure allows for 4 properties that characterize genetic info: 1. Diversity of structure  There is A LOT of ways that base can be arranged and it can vary in length 2. Ability to replicate  DNA replicates by unwinding the 2 strands and building a new strand that is complementary (bases) to the original strand 3. Mutability  During replication, mutations occur which cause different molecules to be encoded and passed on to the offspring 4. Translation into form and functions  Machineries function to translate for proteins and their AA Specifying the AA sequence of a Protein - Transcription and translation occurs to make a proteins from a nucleotide sequence (Figure 1-5) 1. Transcription o Occurs in the nucleus o Purpose: DNA  mRNA (Uracil instead of Thymine) 1. DNA  separates and one strand becomes the template strand to build  Primary RNA 2. Primary RNA  splicing of introns and joining exons and capping  mature RNA 3. Mature RNA  leaves nucleus to cytoplasm  mRNA 2. Translation o Occurs in the cytoplasm o Purpose: mRNA  AA chains (Figure 1-6) 1. Ribosome subunits attach to mRNA  read in groups of 3 called a codon every time it slides down the mRNA  64 codons total to encode for 20 AA 2. tRNA  attaches to ribosome sites  carries in the anticodon w/ corresponding AA 3. AA  link by peptide bond 4. Reach a stop codon  ribosome detaches  left with a chain of AA (polypeptide chain) Polypeptide to Protein - Protein: folded polypeptide chain Gene Regulation - A mechanisms regulates when a genome is to be translated since DNA encodes for the regulatory function - RNA POL: enzyme that is responsible for bring in ribonucleotides to synthesize mRNA - Gene regulation occurs when RNA POL attaches to DNA and during initiation of its movement along the DNA sequence o (-) control: Molecules can block the site where POL binds and prevents transcription o (+) control: Other molecules cause the “blocker” to fall off the DNA to allow transcription o i.e. lac operon The Program of Genetic Investigation The Necessity of Variation - even within the same population, individuals can be different - genetic polymorphism: rich source of material for studying the bases of biological variation among individuals - Genetic variation: genetic difference among individuals. o Genetic variation is the focus of 2 genetic methods of studying biological processes 1. Forward Genetics o forward genetics: investigation to determine the genetic cause of the phenotypic difference (start with phenotype  find genotype cause of the physical variation) o To do so, you need to look for patterns of inheritance in the descendant of crosses between individuals having different phenotype 1. cross phenotype A and B 2. note offspring ratio 3. gene that encodes for the variation is found 4. identify molecular and developmental differences between individuals of different genotypes  study of the abnormal variant, mutant, to the normal form, wild type 5. identify the differences in DNA sequencing - at times, multiple genes act together to determine biological properties - multiple genes can be separate by crosses to create mutant individuals in different gene combos (Figure 1-9) 2. Reverse genetics o reverse genetics: investiagtion to determine the results of physical changes through genetic sequences (start with genotype  find result of phenotypic changes) o require knowledge of the gene sequence (signal that indicates the start and end of the gene on a DNA) o advantage: large #s of mutations can be tailor-made 1. start with a normal DNA sequence 2. alter (mutate) the DNA in a specific way OR comparing it with the DNA of other genomes 3. analyze the function of the DNA sequence Genetic Determinism: gene cause everything - Geneticist chos
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