ch 13 sexual life cycles and meiosis

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Ch 13 Sexual Life Cycles and Meiosis. Reproduction and the Transmission of Traits. Living organisms Have ability to reproduce Heredity Transmission of traits from one generation to the next Variation Offspring often differ in appearance from parents and siblings - PowerPoint PPT Presentation


  • Ch 13 Sexual Life Cycles and Meiosis

  • Living organismsHave ability to reproduce

    HeredityTransmission of traits from one generation to the next

    VariationOffspring often differ in appearance from parents and siblings Environmental and genetic influences

    GeneticsScientific study of heredity and variationReproduction and the Transmission of Traits

  • Progeny (or offspring)-Inherit chromosomes from parents

    -DNA in chromosomes encode the genes thatspecify characteristics

    For exampleeye color, blood type, predisposition to disease

  • What are the mechanisms by which chromosomes are passed onto (eukaryotic) offspring?Asexual reproductionSexual reproduction

  • LE 13-2Parent0.5 mmBudAsexual reproductionBud forms by mitosis of parent cellsBud genetically identical to parent

  • Sexual Reproduction Meiosis: formation of haploid gametes (eggs, sperm) in parents

    2. Fertilization: fusion of gametes from opposite parents--> diploid zygote-->mitotic growth-->embryo-->adult

  • LE 13-5KeyHaploid (n)Diploid (2n)Haploid gametes (n = 23)Ovum (n)Spermcell (n)TestisOvaryMitosis anddevelopmentMulticellular diploidadults (2n = 46)FERTILIZATIONMEIOSISDiploidzygote(2n = 46)Human Sexual ReproductionOffspringgenetically uniquefrom parents

  • How many chromosomes are inherited by human zygotes?46 chromosomesor2n= 46n= the number of chromosomes in a set23 from mother, maternal chromosomes23 from father, paternal

  • LE 13-35 mHuman KaryotypeStained metaphasechromosomesfrom humansomatic cellWhy stain metaphasechromosomes?Compact &easier to see com-pared to interphase

  • LE 13-35 mPair of homologouschromosomesSisterchromatidsCentromere

  • Can you tell the difference between a human male and female by the karyotype?Humans have 22 pairs of autosomes (non-sex chromosomes) 1 pair of sex chromosomes

    Female sex ch.: XXMale sex ch.: XY

  • LE 13-35 mHuman KaryotypeMale or female?

  • If somatic cells have two sets of chromosomes (diploid), how do gametes end up with only one set (haploid)?Diploid precursors to the egg and sperm undergo meiosis in the testis and ovary.

  • LE 13-7Homologous pairof chromosomesin diploid parent cellInterphaseHomologous pair of replicated chromosomesChromosomesreplicateMeiosis IDiploid cell withreplicatedchromosomesSisterchromatidsMeiosis IIHomologouschromosomesseparateSister chromatidsseparateHaploid cells withreplicated chromosomesHaploid cells with unreplicated chromosomesOverview of meiosisaka tetradDiploidHaploid

  • LE 13-4KeyMaternal set ofchromosomes (n = 3)2n = 6Paternal set ofchromosomes (n = 3)Two sister chromatidsof one replicatedchromosomesTwo nonsister chromatids in a homologous pairPair of homologouschromosomes(one from each set)Centromere

  • LE 13-8abSisterchromatidsChiasmataSpindleCentromere(with kinetochore)MetaphaseplateHomologouschromosomesseparateSister chromatidsremain attachedMicrotubuleattached tokinetochoreTetradMEIOSIS I: Separates homologous chromosomesPROPHASE IMETAPHASE IANAPHASE IHomologous chromosomes (red and blue) pair andexchange segmentsHomologous recombination (crossing-over)Pairs of homologouschromosomes split upTetrads line up

  • LE 13-8bCleavagefurrowMEIOSIS II: Separates sister chromatidsPROPHASE IIMETAPHASE IIANAPHASE IITELOPHASE I ANDCYTOKINESISTELOPHASE II ANDCYTOKINESISSister chromatidsseparateHaploid daughter cellsformingTwo haploid cellsform; chromosomesare still doubleDuring another round of cell division, the sister chromatids finally separate;four haploid daughter cells result, containing single chromosomes

  • LE 13-9ProphaseDuplicated chromosome(two sister chromatids)Chromosomereplication2n = 6Parent cell(before chromosome replication)ChromosomereplicationMITOSISMEIOSISChiasma (site ofcrossing over)MEIOSIS IProphase ITetrad formed bysynapsis of homologouschromosomesTetradspositioned at themetaphase plateMetaphase IChromosomes positioned at themetaphase plateMetaphaseAnaphaseTelophaseCytokinesisHomologuesseparateduringanaphase I;sisterchromatidsremain togetherSister chromatidsseparate duringanaphaseDaughtercells ofmeiosis IHaploidn = 3Anaphase ITelophase IMEIOSIS IIDaughter cellsof mitosis2n2nnSister chromatids separate during anaphase IInnnDaughter cells of meiosis II

  • Mitosis producestwo genetically identical diploid cellsMeiosis producesfour genetically distinct haploid cells

  • Mechanisms of Genetic Variation Among OffspringCaused by Sexual ReproductionCrossing over (homologous recombination) (Prophase I)

    2. Independent assortment of chromosomes(Metaphase I & II)

    3. Random fertilization (post-meiosis)

  • LE 13-11Prophase Iof meiosisTetradNonsisterchromatidsChiasma,site of crossingoverRecombinantchromosomesMetaphase IMetaphase IIDaughtercellsRecombinationChiasmata, pl

  • LE 13-10KeyMaternal set ofchromosomesPaternal set ofchromosomesPossibility 1Possibility 2Combination 2Combination 1Combination 3Combination 4DaughtercellsMetaphase IIMetaphase ITwo equally probablearrangements ofchromosomes atIndependent Assortment

  • Random FertilizationAny sperm can fuse with any ovum (unfertilized egg)

    a (human) zygote has about 64 trillion diploid combinations

    Each zygote has unique genetic identity

  • I think they were talking about us. I hope they had it right!If not maybe we can answer questions.

  • See meiosis animationWhat is missing?


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