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Meiosis (necessary for sexual reproduction) Reduction Division sex cells egg/sperm (germ cells) 2N diploid N haploid ???why?? Humans 46 chromosomes 23.

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Presentation on theme: "Meiosis (necessary for sexual reproduction) Reduction Division sex cells egg/sperm (germ cells) 2N diploid N haploid ???why?? Humans 46 chromosomes 23."— Presentation transcript:

1 Meiosis (necessary for sexual reproduction) Reduction Division sex cells egg/sperm (germ cells) 2N diploid N haploid ???why?? Humans 46 chromosomes 23 chromosomes Sexual Reproduction (N) gametes combine 2N diploid # restored) Diversity (combine 2 sets of genes) ?effects on evolution Shuffling during synapsis Xing over of homologous prs in Prophase 1 Draw egg (N) + sperm (N) cell fertilization 2N diploid # restored

2 Meiosis # of chromosomes is cut in 1/2 thru separation of homologous chromosomes in a diploid 2N cell 2N 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 trait Sex cells undergo meiosis to produce Gametes (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 chromosomes between male + female Homologs: chromosomes themselves Cell that contains both sets of homologous chromosomes (from each parent) = 2N diplod 2N diploid cells contain 2 complete sets of genes- 1 from each parent Gametes/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 & original Stages of Meiosis Meiosis I Interphase 1: Chromosomes replicate (S Phase) Growth & development (G 1 phase) Organelle synthesis (G 2 phase) Chromosomes condense & coil Centrioles replicate

5 Prophase 1: Chromosomes visible Each chromosome seeks its homologous pr to form tetrad in synapsis (maternal + paternal) Shuffling: way/side homologous pr ends up on CHANCE! Xing over: between homologus prs exchange of genetic info on chromatids new combos of genes Centrioles migrate & spindles form Homologous prs migrate to spindle fibers Nuclear membrane breaks Shuffling demo- line students up on opposite sides Include Xing over using appendages

6 Metaphase 1: Spindle fibers attached to chromosomes – at kinetocore Tetrads (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 to opposite poles along spindle fibers Nondysjunction: homologous pr(s) fail to separate gametes w/ too many/few chromosomes Ex. Trisomy 21 Down Syndrome Kleinfleters 47XXY Turners 45XO Jacobs 47XYY Polyploidy: nondysjunction of entire set of chromosomes 3N, 4N, etc Fatal in animals Can be in plants hearty, disease resistant, big!

8 Telophase 1: Followed by cytokinesis (division of cytoplasm) Chromosomes gather in nuclei Nuclear membrane reforms Cells 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 Replication Synthesis of organelles Chromatin mesh

10 Prophase II: Chromosomes condense, coil visible Centrioles migrate & spindles form Chromosomes migrate to spindles attach at kinetocore

11 Metaphase II: Chromosomes line up on equator

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 Earth Country State City People Cell Chromosome Chromosome fragment Gene Nucleotide base pairs Section 11-5 Comparative Scale of a Gene Map Mapping of Earths Features Mapping of Cells, Chromosomes, and Genes

14 Telophase II: followed by Cytokinesis Chromosomes gather & Nuclear membrane reforms Produces 4 haploid (N) gametes/sex cells for sexual reproduction


16 Meiosis II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II 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. Section 11-4 Figure Meiosis II

17 How does Xing over affect inheritance? It changes the combo of alleles on the chromosomes Ex. fruit fly w/ red eyes & brown body or white eyes & yellow body Xing over red eyes w/ yellow body and white eyes w/ brown body Xing over used to map genes closer 2 genes are located on a chromosome the Less likey theyll be separated by xing over By observing how frequently Xing over separates any 2 genes helps determine genes relative position on chromosome


19 Mitosis vs Meiosis

20 2 identical daughter cells4 genetically different cells 2N diploid 2N diploid N haploid AsexualSexual 1 division2 divisions Body/Somatic cellsSex Cells Growth Development Repair Produce gametes (egg/ovum & sperm) Less genetic diversity genetic diversity (genes from 2 parents combine, Prophase 1 shuffling (in synapsis), Xing over Occurs after fertilization/ formation of Zygote growth & differentiation Occurs at puberty

21 Gametogenesis: formation of gametes 2N diploid N haploid Spermatogenesis Sperm Formation Oogenesis 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

24 Spermatogenesis vs Oogenesis

25 MalesFemales 4 viable haploid sperm cells 1 viable haploid egg/ovum + 2 or 3 polar bodies SmallLargest cell in human body MotileNon motile Produced in testesProduced in ovaries (*follicle) Produce millions at a timeProduce 1/month = division of cytoplasm division of cytoplasm Occurs at Puberty

26 Karyotype: Chromosome map Cells must be undergoing mitosis for chromosomes to be visible. Count chromosome prs, look for abnormalities Ex. Nondysjunction, Translocation, Inversion of chromosomes Normal male

27 Normal female



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