Week 1 Lecture Notes
Week 1 Lecture Notes BSC2010
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This 6 page Class Notes was uploaded by Isabella Greenspoon on Friday February 20, 2015. The Class Notes belongs to BSC2010 at University of Florida taught by Dr. Fatma Kaplan in Spring2015. Since its upload, it has received 132 views. For similar materials see Integrated Principles of Biology 1 in Biology at University of Florida.
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Date Created: 02/20/15
Dr Kaplan Lecture Notes Genetics the study of heredity Heredity transmission of biological traits from parent to offspring and from generation to generation 0 Three levels of genetic study Molecular genetics DNA RNA proteins Mendelian classical genetics Cells individuals Population and evolutionary genetics populations species and higher groups Chromosome carry DNA and genes across generations from celltocell individual to individual 0 DNA or RNA 0 One DNA molecule double helix per unduplicated chromosome 0 One DNA molecule per sister chromatid of each duplicated chromosome Homologous chromosomes homologs chromosomes of same size shape and centromere position 0 Most importantly chromosomes that carry DNA for same genes Diploid 2n each different chromosomes represented by two homologous chromosomes homologs Haploid n each different chromosome represented by one homolog Karyotype re ects the number and sized of its condensed chromosomes 0 Analysis can be used to identify organisms but DNA sequence is more commonly used Diplontic life cycle organism is diploid and the gametes are the only haploid stage Mitosis faithfully duplicate cells for growth and repair 0 Parent cell 2n 0 lnterphase chromosomes duplicate and the copies remain attached to each other 0 Prophase in the nucleus the chromosomes condense and become visible spindle forms in cytoplasm o Prometaphase nuclear membrane breaks apart spindle starts to interact with the chromosomes 0 Metaphase chromosomes line up at the midline of the cell equatorial position 0 Anaphase chromatids separate and the daughter chromosomes move away from each other towards the poles o Telophase occurs after the chromosomes have separated and is the last phase of mitosis 0 Two daughter cells both diploid each 2n Cyclindependent kinases Cdk regulatory proteins that control the rate of progression through the cell cycle 0 Cdk s are activated by the binding of speci c protein cycHns o Activated Cdk s act to phosphorylate other regulatory proteins thereby activating or deactivating them This activation or deactivation of downstream regulatory proteins more directly determines whether a cell continues through the cell cycle Meiosis l functions 0 Reduces diploid cells to haploid o Generates genetic variation 0 Stages Parent cell 2n Prophase l homologous chromosomes each with a pair of sister chromatids line up to form a tetrad Adjacent chromatids of different homologs break and rejoin chiasma forms Chiasma is resolved recombinant chromatids contain different homologs Metaphase l tetrads line up on the metaphase plate Anaphase l homologous pairs separate Telophase l Cytokinesis Four daughter cells all haploid each n Meiosis ll separation of sister chromatids but in haploid cells Prophase ll Metaphase ll chromosomes line up on the metaphase O O O O 0 plate Anaphase ll sister chromatids separate Telophase ll Cytokinesis ll 4 haploid daughter cells are formed each having only one chromosome of each homologous pair 0 Genetic variation diversity best bet for longterm survival in an uncertain everchanging environment Recombination generation of new gene combinations or arrangements different from the parents 0 Sexual recombination random fertilization of gametes Independent assortment random shuf ing of unlinked genesnonhomologous chromosomes into gametes 2quotn number of possible gametes for a diploid individual with n haploid chromosomes 0 Ex 8388608 gametes per man or woman O Coupled with sexual recombination 0 Early experiments with genetics yielded two theories 0 O O O Blending inheritance Hereditary factors genes are not discrete but rather like quotpaintsquot Particular inheritance hereditary factors are discrete such that they retain their individual identities Gregor Mendel experiments on plant hybridization 1866 Scienti c method hypotheses tested with critical methods Character observable physical feature ex ower color seed shape Trait form of a character ex purple owers or white owers wrinkled seeds 0 Mendel worked with truebreeding varieties when plants of the same variety were crossed all offspring plants produces the same seeds and owers Monohybrid Cross 0 0 Two true breeding lines crossed parental lines F1 100 purple F1 selfpollinated F2 both purple and white 34 purple 14 white Thus classic 31 phenotypic ratio Phenotype what we see and observe Genotypic ratio 121 Heritable factors come in pairs Factors are discrete not miscible like plants Law of segregation 1st law Genes come as pairs of alleles which segregate during meiosis Fertilization restores the paired condition of the genes 0 Test Cross 0 O O Mating of dominant individual with homozygous recessive parent To determine whether dominant individual is homozygous or heterozygous dominant Progeny if variable both purple and white then unknown dominant parent is variable too Pp lf instead 100 constant then unknown dominant parent is constant too PP All offspring receive the same recessive allele from their recessive parent Thus progeny phenotypes are determined by what allele they receive from their unknown dominant parent 0 Law of Independent Assortment 2quot 39 law alleles of unlinked genes shuf e themselves into gametes separately randomly or by chance of each other 0 Occurs in metaphase 1 of meiosis o Dihybrid cross Seed shape dominant round R vs recessive wrinkled r Seed color dominant yellow Y vs recessive green y Phenotypic ration 9331 One of Mendel s contributions to genetics was the use of mathematical analyses the rules of statistics and probability 0 Analyses revealed patterns that allowed him to formulate his hypotheses 0 Probability calculations and Punnett squares give the same results 0 Probability 0 1 if event is certain to happen 0 0 if event cannot happen 0 All other events have a probability between 0 and 1 0 Joint probability multiply the individual probabilities multiplication rule 0 Probability in a monohybrid cross 0 After selfpollination of an F1 Rr the probability that the F2 offspring will have the genotype RR is 12 x 12 14 the same for rr offspring 0 There are two ways to get a heterozygote Rr the probability is the sum of the individual probabilities addition rule 39 14 14 12 0 Extensions on standard Mendelian crosses o Mendel s rst and second laws will continue to hold 0 But we will need to extend these laws New ways for interaeic interactions at one gene nteraleic interactions between multiple different genes Environmental effects on traits Gene linkage o Phenotype interallelic ntergenic Environmental lnterallelic modes of dominance complete incomplete codominance Betweengene interactions epistasis quantitative inher ance Environemtnal in uences penetrance expressivity etc No linkage independent assortment Linkage o Autosomal linkage Sex X chromosome linkage 0 Y chromosome Holandric linkage o Extranuclear linkage to DNA outside of nucleaus Modes of domincance how the two alleles of a heterozygote interact to determine the heterozygous phenotype 0 Complete heterozygous phenotype is indistinguishable from one of the two homozygous phenotypes Heterozygous phenotype same as that of homozygous dominant o lncomplete heterozygous phenotype is intermediate to that of the both homozygous phenotypes o Codominance both alleles of heterozygote are maximally expressed multiple alleles 3 or more alleles for a gene in a population ABO Blood System Three alleles IquotA IAB IquotO IAA and IAB both are completely dominant to lquotO lquotA and lquotB alleles produce speci c antigens A and B 0 Multiple alleles in the whole population some genes have more than 2 alleles Single diploid individual can have only two different alleles for a gene 0 However there can be many mire than two alternative alleles for a gene within that individual s population If so multiple alleles Genotypes n nn12 Ex n3 for BO gene so 6 different genotypes Dominant alleles do not somehow inactive or destroy recessive alleles 0 Instead dominancerecessive is about how the protein products of the 2 alleles of a heterozygote collectively affect the targeted biochemical reaction 0 Dominant allele is not necessarily the most common in the population 0 The dominant allele is also not necessarily the most t allele Epistasis an allele of one gene affects the phenotypic expression of an allele of a second gene 0 Ex dog color First gene controls dark pigmentation Black B dominant to brown b Second gene controls pigment deposition Pigment deposited E dominant to no pigment deposited e 934 phenotypic ratio 0 Quantitative inheritance o Polygenic inheritance multiple genes for same trait 0 Typically continuous characters 0 Strong environmental component 0 Mode of inheritance for many key biological traits ex height weight IQ 0 Different dominant alleles of each gene contribute small additive increment to the trait 0 Number or dominant alleles determines average size not the particular allelic combination 0 Pleiotropy one gene affects many traits Environmental effects 0 Most traits are not completely determined by genotype Penetrance percentage of individuals with given genotype who actually show the associated trait o Expressivity degree to which a penetrant individual shows the associated trait how severe it is o Phenocopy environmentally induced trait that mimics a genetically determined one Traits are determined by the interaction between ones genotype and environment 0 Application of Mendelian genetics to pedigree o Pedigree family tree or genealogy which is used to trace the transmission of a trait
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