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

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 sperms) Symbols ________ ________

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 ________)

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

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

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)

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!

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

Meiosis II (like mitosis- w/ no DNA replication) Interphase II: No DNA Replication Synthesis of organelles Chromatin mesh

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

Metaphase II: Chromosomes line up on equator

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)

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

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

Mitosis vs Meiosis

2 identical daughter cells4 genetically different cells 2N diploid  2N diploid2N diploid  N haploid AsexualSexual 1 division2 divisions Body/Somatic cellsSex Cells Growth Development RepairProduce 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

Gametogenesis: formation of gametes 2N diploid  N haploid Spermatogenesis  Sperm Formation Oogenesis  Egg (ovum) Formation

Spermatogenesis: males, in the testes produces 4 viable sperm cells (small)

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

Spermatogenesis vs Oogenesis

MalesFemales 4 viable haploid sperm cells1 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

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

Normal female