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Meiosis (necessary for sexual reproduction)

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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 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 (G1 phase) Organelle synthesis (G2 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 Kleinfleter’s 47XXY Turner’s 45XO Jacob’s 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 Comparative Scale of a Gene Map
Section 11-5 Mapping of Earth’s Features Mapping of Cells, Chromosomes, and Genes Cell Earth Country Chromosome Chromosome fragment State Gene City People Nucleotide base pairs

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


16 Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II Anaphase II Telophase II Meiosis 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 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 they’ll 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 Mitosis vs Meiosis 2 identical daughter cells 4 genetically different cells 2N diploid 2N diploid 2N diploid  N haploid Asexual Sexual 1 division 2 divisions Body/Somatic cells Sex 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 Spermatogenesis vs Oogenesis
Males Females 4 viable haploid sperm cells 1 viable haploid egg/ovum + 2 or 3 polar bodies Small Largest cell in human body Motile Non motile Produced in testes Produced in ovaries (*follicle) Produce millions at a time Produce 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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