Week 1 Notes: Bio 22
Week 1 Notes: Bio 22 BIOL 222
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This 10 page Class Notes was uploaded by Gabrielle Woolery on Tuesday August 30, 2016. The Class Notes belongs to BIOL 222 at Pennsylvania State University taught by Paul Babitzke in Fall 2016. Since its upload, it has received 159 views. For similar materials see Genetics in Biology at Pennsylvania State University.
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Date Created: 08/30/16
Bio 222 Chapter 1: Introduction to Genetics Genetics Study of gene function From molecules of DNA to the Gene pool of a population Division of Genetics Transmission Genetics o Study of genetic information found in genes that is passed from generation to generation Molecular Genetics o Studies gene structure and function at the molecular lever Population Genetics o Studies the changes in frequencies of genes in a whole population over time Central Dogma of Molecular Biology (Information flow) DNA (replication) RNA (transcription Protein (translation) Genes Functional Units of DNA, these are the parts of DNA that code for traits Organisms inherit genes from parents and contribute to the gene pool of a population o Gene pool is the amount of different genes in a single population Genes come in multiple forms called alleles o Alleles differ because each allele is made up of a different amino acid sequence, which aid in making different proteins. The proteins have different functions due to this. Genome Complete set of genetic instructions and genes for an organism Genotype The genetic part that organism inherit. Internal. Set of genes the organism inherits o Ex: Aa, AA, aa Phenotype Characteristics an organism shows. External. o Ex: getting the genotype AA for hair color so the phenotype would be Brown hair if A stranded for brown hair. Environment Interacts with genes which influences the phenotype of organisms o Ex: Someone who is Caucasian has a white skin tone. When it’s sunny out the sunrays influence someone’s skin color to become tan. Phenotypes change over ones lifetime as the environment interacts genes Genetics study partial genotypes and partial phenotypes of an organism o Ex: studying one or 2 genes Gene products (usually proteins) make a protein complex. If one protein is mutated it can have an impact on the protein complex thereby cause bad or good effects in the individual. Wild Type (WT) Genotype and Phenotype of natural populations. Normal gene that is expressed Variant or Mutant Individual that is not MT It has a mutation that can occur in only one gene or more. Mutations are the basis for variation within a species and is the raw material for evolution Model Organisms Some organisms are easier to study than others. Can test certain organisms and relate them to humans. Genetic analysis is greatly simplified by using an easily followed phenotype in an organism that is practical to study. Genetic Dissection Identify a process to study Isolate mutants that disrupt the process Identify and clone the WT genes Determine the function of gene products o Pick, isolate, identify, determine Chapter 2: Chromosomes and Reproduction Genes and Chromosomes Each chromosome contains one DNA molecule and associated proteins o DNA is a duplex N The number of different chromosomes in the cell Cells with 2 chromosome sets are 2n which are diploid Cells with one chromosome set are 1n which is haploid Eukaryotic Chromosome Features Chromosome number 2 to over 100 it depends on the species Chromosome size Size can vastly vary in a genome Centromere Structure that the kinetochore attaches to (constricted appearance at metaphase) It is part of the chromosomes Kinetochore Multi protein complex that assembles around the centromere during metaphase. Spindle fibers attach to it in metaphase Spindle Fibers Attach to kinetochore during mitosis and meiosis Telomeres The end of the chromosomes Cell Cycle Made of Interphase and Mitotic phase Mechanisms exist to make sure cell numbers are balanced Interphase Made up of G1, S, and G2 phases G1 o Non dividing metabolism and cell growth S o DNA synthesis and replication G2 o Metabolism and cell growth Mitosis and Cytokinesis Mitosis: nuclear division Cytokinesis: cell division Mitosis Somatic cells (all but non gamete producing cells) Produces genetically identical daughter cells from one progenitor Single Division o 1 cell gives rise to 2 cells 4 Continuous Stages Stages of Mitosis Prophase o Chromosomes with 2 sisters chromatids condense, nuclear membrane degrades, spindle fibers form o Chromatids are joined at the centromere and remain attached o Think 1 chromosome has two sister chromatids Metaphase o Chromosomes move to equatorial plane o Spindle fibers from opposite centrosomes attach to the kinetochore of each sister chromatid. o Metaphase Plate is at the center of the cell Anaphase o Pairs of sister chromatids are separated and move to opposite ends of the cell Telophase o Nuclear Membrane forms around each set of chromosomes. Cytokinesis Cytoplasm is divided in two by a new cell membrane Progression through the cell cycle is regulated at key transition checkpoints G1/S Checkpoint Holds the cell in G1 until the enzymes necessary for DNA replication are produced. DNA synthesis and replication does not occur until DNA damage is repaired and all the enzymes are synthesized o During replication mismatches can occur so this check point can check for mis matches to minimize mutations Meiosis Production of genetically different gametes 2 cell divisions that result in 4 cells o One meiocyte produces 4 gametes o Meiosis 1 and Meiosis 2 Meiosis 1 Homologous chromosomes separate The two members of each are called homologs Prophase 1 o Chromosomes become visible o Synapsis: homologous chromosomes pair o Crossing over An exchange of DNA between non-sister chromatids Visualized by a cross shaped structure Gene shuffling: breaking and shuffling of DNA during crossing over. (Intra recombination) NON SISTER CHROMATIDS Metaphase 1 o Each pair of homologs are lined up at the equatorial plane o The two centromere of a homologous pair attach to spindle fibers of opposite poles Anaphase 1 o Members of each homologous pair separate and move to opposite poles Telophase 1 o Two daughter cells form Interkinesis No DNA synthesis Number of chromosomes in each cell has been reduced by ½ (2n goes to 1N) aka diploid to haploid Period of time between meiosis 1 and meiosis 2 Meiosis 2 Similar to mitosis where the number of chromosomes in the parental and progeny cells are the same Centromeres divide: separation of sister chromatids Result is 4 haploid 1n gametes Chromosome cut in half and each only one has one chromatid at the end Sequences of meiosis Each meiocyte produces 4 cells Chromosome number is reduced by half Intrachromosomal Recombination Crossing over generate intrachromosomal recombination (new allele combinations) Occurs during prophase one Not sister chromatids Interchromosonal Recombination Random distribution of chromosomes Because of independent assortment in anaphase 1 when the chromosomes are pulled apart What keeps chromatins together until anaphase? Cohesin o Protein that holds sister chromatids together (S through G2 phase) Separase o Degrades cohesion Mitosis: degrades cohesion during anaphase allows separation of sister chromatids Meiosis 1: Degradation of cohesion allows separation of homologous pairs. Cohesion still holds sister chromatids together at the centromere Meiosis 2: Degradation of centromeric cohesion allows separation of sister chromatids Chapter 3: Basic Principles of Heredity Gregor Mendel Conducted quantitative and systematic studies of inheritance with peas Proposed concept of gene o Individual pea plant produces both pollen and eggs o Peas can self pollinate Can fertilize itself Pollen and eggs are from the same flower Both parents have the same genotype o Peas can be cross pollinated Can be fertilized by another plant via bee, wind, etc. carrying pollen New genes can come from this Pollen from one plant fertilizes an egg from another plant Parents may have same or different genotypes o Each pea results from a separate fertilization event Generations Pure Line o All offspring produced by selfing or crossing individuals within the same line have the same phenotype because they have the same genotype P o Parental generation, this is the first cross. They are a pure line which means they are homozygous recessive or homozygous dominant F1 o First filial general (progeny from first cross) o Comes from two different pure lines o To make F2 the self each other o All heterozygous F2 o Second filial generation (progeny from selfing individuals from F1 generation) o Self fertilization from F1 Vocabulary Alleles o Different forms of the same gene (Y and y) o Ex: code for eye color Autosomes o All chromosomes other than sex chromosomes Single Gene Inheritance Patterns Monohybrid Cross o P Generation P pure round seeds (RR) crosses with pure wrinkles seeds (rr) to make F1 generation o F 1 Generation All round seeds that express dominant genotype because they all become heterozygous since its two different pure lines crossing one another o F2 Generation (F1 and other F1 cross so two heterozygotes cross through selfing to make F2) Phenotypic Ratio 3:1 Genotypic ratio 1:2:1 Mendels First Law (Law of equal segregation) The two members of a gene pair segregate from each other into gametes, such that one half of the gametes carry one member of the gene pair and the other half of the gametes carry the other member of the gene pair Genetic Crosses Meiosis Segregation results when homologous chromosomes separate during meiosis Test Cross Crossing an unknown to a homozygous recessive individual TT or Tt X tt o 1:1 Dominant: Recessive (unknown was Tt) o All Dominant (unknown was TT) o This cross helps you find missing allele from the parents Probability The number of times an event is expected to happen divided by the number of opportunities for an event to happen Dice o Probability to roll a 3 : 1/6 Gametes o Heterozygous Aa probability to get an A: ½ Probability to get an a: ½ Multiplication Rule The probability that two or more independent events will occur simultaneously is calculated by multiplying there independent probabilities o Dice Probability to get a 2 and a 2 on 2 successive rolls: 1/6 times 1/6 (probability of each is 1/6)= 1/36 o Gametes RrYy the probability to get an R and a Y: ½ times ½ (1/2 is the ability to get one R and one Y) = ¼ Addition Rule Probability of any one of two or more mutually exclusive events is calculated by adding the probabilities of these events o Dice Probability of getting two 2s or two 3s of two successive roles of one die. 1/36 + 1/36 (1/36 for each comes from multiplication rule)= 1/18 o Gametes Gamete with two recessive or 2 dominant alleles ½ times ½ + ½ times ½ = ¼ + ¼ = ½
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