Presentation on theme: "Meiosis (necessary for sexual reproduction)"— Presentation transcript:
1 Meiosis (necessary for sexual reproduction) Reduction Division sex cells egg/sperm (germ cells)2N diploid N haploid ???why??Humans chromosomes 23 chromosomesSexual Reproduction (N) gametes combine2N diploid # restored)↑ Diversity (combine 2 sets of genes) ?effects on evolutionShuffling during synapsisXing over of homologous prs in Prophase 1Draw egg (N) + sperm (N) cell fertilization2N diploid # restored
2 Meiosis# of chromosomes is cut in 1/2 thru separation of homologous chromosomes in a diploid 2N cell2N diploid cell contains 2 complete sets of chromosomes(1 set of chromosomes/genes from each parent)Mendel: All of an organisms cells except gametes contain 2 alleles for a traitSex cells undergo meiosis to produceGametes (ovum/egg and sperm)Symbols ________ ________
3 Somatic/Body cells 46 chromosomes (23prs) 22 prs/44 autosomes –not sex chromosomes (#’s1-22)1 pr/2 sex chromosomes (#23)Homologous Chromosomes: Corresponding chromosomesbetween male + femaleHomologs: chromosomes themselvesCell that contains both sets of homologous chromosomes(from each parent) = 2N diplod2N diploid cells contain 2 complete sets of genes-1 from each parentGametes/Sex cells contain only a single copy (1 set) of genes b/c alleles (forms of a gene) are separated during gamete formation (oognesis _____ and spermatogenesis ________)
4 Meiosis: produces 4 haploid cells (N) Genetically different from each other & originalStages of MeiosisMeiosis IInterphase 1: Chromosomes replicate (S Phase)Growth & development (G1 phase)Organelle synthesis (G2 phase)Chromosomes condense & coilCentrioles replicate
5 Prophase 1: Chromosomes visible Each chromosome seeks its homologous pr to formtetrad in synapsis (maternal + paternal)Shuffling: way/side homologous pr ends up on CHANCE!Xing over: between homologus prs exchange of genetic info onchromatids new combos of genesCentrioles migrate & spindles formHomologous prs migrate to spindle fibersNuclear membrane breaks ↓Shuffling demo- line students up on opposite sidesInclude Xing over using appendages
6 Metaphase 1: Spindle fibers attached to chromosomes – at kinetocoreTetrads (homologous prs) line up on equator**Chance which side maternal/paternal pr ends up on(w/ rest of genes on chromosomes on that side)
7 Anaphase 1: Dysjunction Homologous chromosomes (each w/ 2 chromatids) move toopposite poles along spindle fibersNondysjunction: homologous pr(s) fail to separate gametes w/ too many/few chromosomesEx. Trisomy 21 Down SyndromeKleinfleter’s 47XXYTurner’s 45XOJacob’s 47XYYPolyploidy: nondysjunction of entire set ofchromosomes 3N, 4N, etcFatal in animals Can be in plants hearty,disease resistant, big!
8 Telophase 1: Followed by cytokinesis (division of cytoplasm) Chromosomes gather in nucleiNuclear membrane reformsCells contain a single set of chromosomes/genes (N-haploid)2, haploid, (N) Daughter cells
9 Meiosis II (like mitosis- w/ no DNA replication) Interphase II: No DNA ReplicationSynthesis of organellesChromatin mesh
10 Prophase II: Chromosomes condense, coil visible Centrioles migrate & spindles formChromosomes migrate to spindles attach at kinetocore
12 Anaphase II: Sister chromatids separate & move towards opposite poles along spindle (Nondysjunction can occur here also)** b/c of shuffling & Xing over in Prophase I each cell has a different genetic makeup- combo of genes in each gamete Random**chromosomes carry genes & genes carry alleles (forms of a gene) for specific trait (chromosome carry genes for specific traits DNA)
13 Comparative Scale of a Gene Map Section 11-5Mapping of Earth’s FeaturesMapping of Cells, Chromosomes, and GenesCellEarthCountryChromosomeChromosome fragmentStateGeneCityPeopleNucleotide base pairs
14 Telophase II: followed by Cytokinesis Chromosomes gather & Nuclear membrane reformsProduces 4 haploid (N) gametes/sex cells forsexual reproduction
16 Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II Metaphase IIAnaphase IITelophase IIMeiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.The chromosomes line up in a similar way to the metaphase stage of mitosis.The sister chromatids separate and move toward opposite ends of the cell.Meiosis II results in four haploid (N) daughter cells.
17 How does Xing over affect inheritance? It changes the combo of alleles on the chromosomesEx. fruit fly w/ red eyes & brown body or white eyes & yellow bodyXing over red eyes w/ yellow body and white eyes w/ brown bodyXing over used to map genes closer 2 genes are located on a chromosome the Less likey they’ll be separated by xing overBy observing how frequently Xing over separates any 2 genes helpsdetermine genes relative position on chromosome
20 Mitosis vs Meiosis2 identical daughter cells4 genetically different cells2N diploid 2N diploid2N diploid N haploidAsexualSexual1 division2 divisionsBody/Somatic cellsSex CellsGrowth Development RepairProduce gametes (egg/ovum & sperm)Less genetic diversity↑ genetic diversity (genes from 2 parents combine, Prophase 1 shuffling (in synapsis), Xing overOccurs after fertilization/ formation of Zygote growth & differentiationOccurs at puberty
21 Gametogenesis: formation of gametes 2N diploid N haploid Spermatogenesis Sperm FormationOogenesis Egg (ovum) Formation
22 Spermatogenesis: males, in the testes produces 4 viable sperm cells (small)
23 Oogenesis: females in the ovaries (follicle in ovary is where mature egg develops)produces 1 egg/ovum (lgst cell in body) + 2 or 3 polar bodies≠ division of cytoplasm ovum gets all the nutrients (why)?Travels thru fallopian tube (propeled by cilia) for fertilization by sperm
25 Spermatogenesis vs Oogenesis MalesFemales4 viable haploid sperm cells1 viable haploid egg/ovum + 2 or 3 polar bodiesSmallLargest cell in human bodyMotileNon motileProduced in testesProduced in ovaries (*follicle)Produce millions at a timeProduce 1/month= division of cytoplasm≠ division of cytoplasmOccurs at Puberty
26 Karyotype: Chromosome map Cells must be undergoing mitosis for chromosomes to be visible.Count chromosome prs, look for abnormalitiesEx. Nondysjunction, Translocation, Inversion of chromosomesNormal male
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