2 Reproduction and the Transmission of Traits Living organismsHave ability to reproduceHeredityTransmission of traits from one generation to the nextVariationOffspring often differ in appearance from parents and siblingsEnvironmental and genetic influencesGeneticsScientific study of heredity and variation
3 Progeny (or offspring) -Inherit chromosomes from parents-DNA in chromosomes encode the genes thatspecify characteristicsFor exampleeye color, blood type, predisposition to disease
4 What are the mechanisms by which chromosomes are passed onto (eukaryotic) offspring? Asexual reproductionSexual reproduction
5 Bud forms by mitosis of parent cells LE 13-2Asexual reproductionBud forms by mitosis of parent cellsBud genetically identical to parentParentBud0.5 mm
6 Sexual ReproductionMeiosis: formation of haploid gametes (eggs, sperm) inparents2. Fertilization: fusion of gametes from opposite parents--> diploid zygote-->mitotic growth-->embryo-->adult
7 Human Sexual Reproduction LE 13-5Human Sexual ReproductionKeyHaploid gametes (n = 23)Haploid (n)Ovum (n)Diploid (2n)Spermcell (n)MEIOSISFERTILIZATIONOvaryTestisDiploidzygote(2n = 46)Offspringgenetically uniquefrom parentsMitosis anddevelopmentMulticellular diploidadults (2n = 46)
8 How many chromosomes are inherited by human zygotes? or2n= 46n= the number of chromosomes in a set23 from mother, maternal chromosomes23 from father, paternal “
9 Human Karyotype 5 µm Stained metaphase chromosomes from human LE 13-3Human Karyotype5 µmStained metaphasechromosomesfrom humansomatic cellWhy stain metaphasechromosomes?Compact &easier to see com-pared to interphase
10 Pair of homologous 5 µm chromosomes Centromere Sister chromatids LE 13-3Pair of homologouschromosomes5 µmCentromereSisterchromatids
11 Can you tell the difference between a human male and female by the karyotype? Humans have22 pairs of autosomes (non-sex chromosomes)1 pair of sex chromosomesFemale sex ch.: XXMale sex ch.: XY
13 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.
14 Overview of meiosis aka tetrad Diploid Haploid LE 13-7 Interphase Homologous pairof chromosomesin diploid parent cellDiploidChromosomesreplicateaka tetradHomologous pair of replicated chromosomesSisterchromatidsDiploid cell withreplicatedchromosomesMeiosis IHaploidHomologouschromosomesseparateHaploid cells withreplicated chromosomesMeiosis IISister chromatidsseparateHaploid cells with unreplicated chromosomes
15 Key Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of LE 13-4KeyMaternal set ofchromosomes (n = 3)2n = 6Paternal set ofchromosomes (n = 3)Two sister chromatidsof one replicatedchromosomesCentromereTwo nonsisterchromatids ina homologous pairPair of homologouschromosomes(one from each set)
16 MEIOSIS I: Separates homologous chromosomes LE 13-8abMEIOSIS I: Separates homologous chromosomesPROPHASE IMETAPHASE IANAPHASE ICentromere(with kinetochore)Sister chromatidsremain attachedSisterchromatidsChiasmataMetaphaseplateSpindleTetradMicrotubuleattached tokinetochoreHomologouschromosomesseparateHomologous chromosomes(red and blue) pair andexchange segmentsHomologous recombination (crossing-over)Tetrads line upPairs of homologouschromosomes split up
17 MEIOSIS II: Separates sister chromatids LE 13-8bMEIOSIS II: Separates sister chromatidsTELOPHASE I ANDCYTOKINESISTELOPHASE II ANDCYTOKINESISPROPHASE IIMETAPHASE IIANAPHASE IICleavagefurrowHaploid daughter cellsformingSister chromatidsseparateTwo haploid cellsform; chromosomesare still doubleDuring another round of cell division, the sister chromatids finally separate;four haploid daughter cells result, containing single chromosomes
18 (before chromosome replication) LE 13-9MITOSISMEIOSISParent cell(before chromosome replication)Chiasma (site ofcrossing over)MEIOSIS IProphaseProphase IChromosomereplicationChromosomereplicationTetrad formed bysynapsis of homologouschromosomesDuplicated chromosome(two sister chromatids)2n = 6Chromosomespositioned at themetaphase plateTetradspositioned at themetaphase plateMetaphaseMetaphase IAnaphaseSister chromatidsseparate duringanaphaseHomologuesseparateduringanaphase I;sisterchromatidsremain togetherAnaphase ITelophaseCytokinesisTelophase IHaploidn = 3Daughtercells ofmeiosis I2n2nMEIOSIS IIDaughter cellsof mitosisnnnnDaughter cells of meiosis IISister chromatids separate during anaphase II
20 Mechanisms of Genetic Variation Among Offspring Caused by Sexual Reproduction Crossing over (homologous recombination)(Prophase I)2. Independent assortment of chromosomes(Metaphase I & II)3. Random fertilization (post-meiosis)
21 Recombination Chiasmata, pl Prophase I of meiosis LE 13-11 Nonsister chromatidsRecombinationProphase Iof meiosisTetradChiasma,site ofcrossingoverChiasmata, plMetaphase IMetaphase IIDaughtercellsRecombinantchromosomes
22 Independent Assortment LE 13-10Independent AssortmentKeyMaternal set ofchromosomesPossibility 1Possibility 2Paternal set ofchromosomesMetaphase ITwo equally probablearrangements ofchromosomes atMetaphase IIDaughtercellsCombination 1Combination 2Combination 3Combination 4
23 Any sperm can fuse with any ovum (unfertilized egg) Random FertilizationAny sperm can fuse with any ovum (unfertilized egg)a (human) zygote has about 64 trillion diploid combinationsEach zygote has unique genetic identity
24 I think they were talking about us. I hope they hadit right!If not maybe we cananswer questions.
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