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    Molecular and General Genetics 2014 Biol261/2

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    The science of genetics is relativelynew.

    Modern breeding designs andmolecular capabilities have acceleratedthe pace and scope of understanding thenature of genes and characterexpression, promising a biologicalrevolution

    But, the fabric of this revolution isbuilt using an ,applies various causaloperating at different levels of

    (organismal andmolecular) that are at well integratedin .

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    DEFINITIONSGenetics is defined as:

    (1) The studyofgenes(2) The studyof inheritance. (Griffiths et al. 9e)The study ofall aspects of genes(Griffiths et al. 10e)(3)Genetics is the study ofheredity and variation(Lewontin 1974)

    Genetics is studied on different natural scalesof organization: molecular, chromosomal,transmission genetics, population and evolutionary

    genetics, genomics.

    Consequently, for example, definitions of a gene differwith the scale and nature of the study.

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    ClassicalGeneticsModel I involve genes (only) governing theexpression of a character or phenotype:genetic determination- a

    set of instructions for turning undifferentiated environmentalmaterials into making a specific organism, regardless of theenvironment.

    GeneticDeterminism

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    Model II:Environmental determinism Expressed DNAcontains the information, but the local environment (internal orexternal)determines the actual course of development or theexpression of a character state. For example, gene expressionmay be governed by chromosomal tags or intervening sequences,sex in turtles and crocodiles is determined by eggdevelopment temperature.

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    Model III:genotype - environment interaction - The courseof development, or phenotypeexpression depends on the

    genes an individual inherits from its parents and thesequence of specific environments an individual encountersduring development.

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    Figure 1-18

    Genes and the environment both influenceeye size in Drosophila

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    Our understanding of Genetics, summarized by the authors ofyour text book, pre-eminent geneticist of our generation, is.. Genescannot generate or even dictate the structure of an organism bythemselves. The environment (internal or external) has a crucial

    ongoing effect and sometimes it is a controlling component ofexpression. Ch 1, Griffiths et al 9thedition.

    Nonetheless: Many write, talk and act as if genes alonedetermine phenotype expression.

    In some cases this appears correct, in others this may be amisleading characterization.

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    Development variation unrelated to known or controlled allelic orenvironmental variation, may produce asymmetrical or highly

    variable characters. Thisdevelopmental noisecauses variability

    not related to specific environments or genes

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    Textbooks:

    An Introduction to Genetic AnalysisGriffiths et al. 10thedition - required.

    Solutions Manualfor An Introduction to

    Genetic Analysis -suggested

    I clicker - required

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    WEB Site for Molecular and General Genetics:

    https://www.myconcordia.caChoose Course websites (Moodle)

    Lecture slidesRecommended Problems

    Course outline and grading scheme

    The text book publisher, W.F. Freeman has a web sit

    www.whfreeman.com

    with study aids including animations.

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    Mandatory tutorialsmeet once a week for 2 hr,beginning next week

    A teaching assistant will reviewthe previous weeksmaterial, discussillustrative problems, and a week later,testyou and other students on the lecture material.

    Each week, a section is covered in 2 lectures,say section A. The following week, problems related tosection A are solved in tutorial. Student teams of 4-5 willpresent the solution to a pivotal selected problem.

    In the next week section A will be the subject of the quiz.

    Your tutorial grade will be largely based on your quiz marksand yourpresentation scores.

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    The readings in the text and the assignedproblems are in the dates reading andproblems EXCEL file

    (Biol 261 Schedule.xls)

    For example,Week 1

    ReadCh: 1, 2.0-2.2, 2.4-2.6

    PrintCh 2: 15, 18, 28,31,33,34,40,43,50,51,61,63,64

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    Grading:

    20% Tutorial

    40%

    2 Midterm Exams40% Final

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    SECTION 1 : Classic Genetics

    Mendelian Genetics 1 gene, 2 alleles

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    Scientific genetics beganwith Gregor Mendelwho in

    the 1850s used differentpure-breeding strains in acontrolled breedingexperiment to test their mode

    of inheritance.

    See C. Stern and E.R. SherwoodThe Origin of Genetics a MendelSource Book

    The laws of inheritance were independentlyrediscovered in 1900 by Hugo de Vries,

    Carl Correns, and Erich von Tschermak.

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    Single Gene Inheritance

    During Mendels university education inbotany, breeding and physics,physicists were

    interested in the atomic nature of matter.

    John Dalton is considered the originator ofmodern atomic theory. But Daltons atomichypothesis did not specify the size of atoms.

    Therefore it was a major landmark when in1865 Johann Josef Loschmidtmeasured thesize of the molecules that make up air.

    Loschmidtwas also from the Czech Republic aprofessor of Physics in Vienna inevitably part

    of Mendels education.

    So it was not surprising that Mendel set out to lookfor the atoms of inheritance.

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    A) Experimental Control. Start with a

    population, any sexual populationis

    defined by the extent ofpotentially

    interbreeding individuals. In Mendels

    case he restricted breeding individuals

    to the strains he used within his garden

    plot below.

    The more control you have over its

    ecology, you decrease the influence

    of chance effects of the environmenton inheritance and expression.

    But, there are always other levels of

    chance variation.

    B) Statistics One of Mendels

    conceptual breakthroughs in dealingwith this variation was his statistical

    approach, the larger the sample size

    (statistical) , and the more factors

    you control (experimental), the

    smaller the influence of chance

    effects on the experimental

    outcome.

    Foundations Experimental Control and Statistics

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    Inbred,pure breeding (selfed or bred withan individual from the same strain),

    colored (Purple ish), Psium sativumParental line

    X

    X

    Inbred Strain

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    X

    X

    Second (white) pure breeding,inbred Parental line

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    Alternative Hypotheses:(1)Discrete categorical inheritance or

    (2) Blending continuous inheritance

    Test: crossing inbred white and purple-floweredpea strains, are colors retained in hybrids,

    through several generations or are they lost,changed or otherwise altered (blended) indifferent offspring generations?

    Methods:(1) define the character-flower color(white, purple with no intermediates), then

    (2) the breeding design.

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    Controlfor differences

    in the cross of pure-breeding parentalstrains

    Reciprocal CrossesMale purple pollen to

    white stigma (shown),and male white pollentopurple stigma (notshown).

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    XParentals

    (F1)

    Discrete or Blending Inheritance?

    Breeding design: Reciprocal Monohybrid Cross

    Inbreed or self fertilize the (F1).

    In the first generation: there was no blending butthere was evidence of possible character loss.

    first filial generation

    50% 50%

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    Parental Cross

    F1:observations?Interpretation

    X

    X

    Count224 white (0.24 total)705 purple (0.76 total)

    (1: 3.15)

    F2:observations

    Odd fact -the ratiochanged from 50/50 in the

    parentals, 100% purple inthe F

    1 to 3:1 in the F

    2?

    Interpretation

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    F2

    225 white, 705 purple or 3:1

    Test the particle variation by inbreeding F2plants

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    F2

    F3

    Inbreed (self)

    (pp) (pP) (PP)

    Dominance hides the frequency of different particles,gametes or alleles -actually 50% p /50%P

    Dominance is an empirical description, anempirical fact without a specific mechanism.

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    Causality of phenotypic variation inMendel s experiment is best described as:

    a)Genetic determination

    b)

    Environmental determination

    c)

    Gene-environment interaction

    d) Developmental noise

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    Mendels other hybrid crosses confirm the 3:1 characterorphenotype ratio in inbred dominant and recessive charactercrosses

    Mendels data demonstrates that genetic facts are

    statistical facts. You can not predict a exact phenotypebut in a breeding design you can assign an expected

    probability .

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    MENDELS FIRST LAW: EQUAL SEGREGATION OF ALLELES

    Mendels Model

    (1)

    Inherited germinal or pollen particles for each character orgenesmayhavegenes in different states calledalleles(variation)

    (2) Individuals have 2 copies of each gene (gene pairs). If thestates of each gene are the same they are calledhomozygotes(pp or PP), if alleles are different they are calledheterozygotes(Pp).

    (3) Each parental gene segregatesrandomly into a gamete(spermor eggs) or individuals in a pair are segregated into different

    gametes.(4) Parental sex causesgene copies to recombineforming the F1and F2 offspring, which have allele pairs from both parents.

    (5) Individual offspring have two copies of each allele, either oneof which may or may not be dominant (P) or recessive (p).

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    P

    p

    0.5 purple gametes inbreeding population

    P: Monohybrid Cross : white (pp) and purple (PP)flowers

    0. 5

    wh

    ite g

    am

    et e

    sin

    b re

    ed

    ing

    p o

    p u

    latio

    n

    Punnett SquareModel of equal segregation andrandom recombination

    The breeding population consists of equal numbersof white and purple parents, hence,

    you expect 50% p alleles, 50 % P in the F1

    F1

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    0.5 P

    0.5 p All Ppdiploids

    purple gametes in thebreeding population

    P: Reciprocal monohybrid cross (pp x PP)

    whi t

    ega

    m e

    tes

    b re

    ed

    ing

    p o

    p u

    latio

    n

    Punnett SquareModel

    F1 Offspring Expectationbased on equal segregationand random recombination. All heterozygotes

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    P p

    P

    p

    0.5 1/2

    0.5

    1/2

    Pp x Pp

    F1 PunnettSquare

    Inbreed (heterozygote)individuals

    F2expected

    values

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    P p

    P

    p

    PP1/4

    Pp1/4

    Pp1/4

    pp1/4

    0.5 1/2

    0.5

    1/2

    Pp x Pp

    F1 PunnettSquare

    Inbreed (heterozygote)individuals

    F2

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    Terms to define: Monohybrid cross, genes, alleles, allele

    frequency, dominance, monohybrid, homozygote,heterozygote genotype, breeding design, inbreeding andoutbreeding.

    Know: genetic models (I-IV);Mendel 1: the monohybrid cross breeding design, includingthe meaning of inbreeding and outbreeding, first and secondfilial crosses; Mendels first law -what it means, PunnettSquare.

    Monohybrid breeding design - Parentals, expectations F1, F2