Meiosis vs. Mitosis Animation

2. Meiosis vs. MitosisAnimation • 2 divisions • daughter cells genetically differentfrom parent • produce 4 cells • 2n  1n • produces gametes • crossing over!! • 1 division • daughter cells genetically identical to parent • produces 2 cells • 2n  2n • produce cells for growth & repair • NO crossing over • division • Begins with interphase • PMAT

4. Meiosis Stages of Meiosis Review BioFlix Animation Unique Features of Meiosis

5. Crossing Over • Homologous Chromosomes • Synapsis • Chiasma form • Cross over at matching regions of nonsisterchromatids • genetic recombination increases variation!!! • Process itself varies • Bacteria – asexual reproduction

6. 46 46 46 46 46 46 46 46 46 46 23 23 46 23 23 Putting it all together… gametes meiosis  fertilization  mitosis + development meiosis egg zygote fertilization mitosis sperm development

7. An Intro to Animal Development • Fundamental biological question: How does a single cell—the fertilized egg—develop into a multicellular individual? • Development proceeds in ordered phases through organism’s life cycle: • Gametogenesis • Fertilization • Cleavage • Gastrulation • Organogenesis

9. Gametogenesis – sperm & egg production

10. primary follicles germinal cell (diploid) fallopian tube fertilization developing follicle primary oocyte (diploid) MEIOSIS I mature follicle with secondary oocyte secondary oocyte (haploid) first polar body ruptured follicle(ovulation) MEIOSIS II after fertilization ovum (haploid) second polar body corpus luteum Oogenesis

11. Egg Structure and Function • Relatively large & nonmotile • Size largely due to nutrient storage, required for early embryonic development • Quantity of nutrients varies across species • Relatively small mammalian egg supplies nutrients for early development ONLY  embryos start to obtain nutrition through placenta shortly after fertilization • Egg-laying species form larger eggs yolk of the egg is embryo’s SOLE nutritional source prior to hatching

12. Spermatogenesis Epididymis Testis germ cell (diploid) Coiled seminiferous tubules primary spermatocyte (diploid) MEIOSIS I secondary spermatocytes (haploid) MEIOSIS II Vas deferens spermatids (haploid) spermatozoa • continuous & prolific process • 100-600 million sperm can be produced daily

13. Fertilization - haploid sperm and egg cells fuse to form diploid zygote (a fertilized egg). • Certain conditions MUST be met before a zygote can form: • Location: gametes in same place at same time. • Recognition: recognize & bind to each other. • Fusion! • Trigger onset of development.

14. Successful fertilization leads to development – how do we become a person from 2 single cells? Do you think the process is the same for all living things? Explain and describe your vision of this process.

15. Why Does Only One Sperm Enter the Egg? • Animals use different mechanisms to avoid polyspermy - fertilization by more than one sperm • Ex: sea urchins - fertilization stimulates creation of a physical barrier • Ca2+-based signal is rapidly induced & propagated throughout the egg, form a fertilization envelope keeps away additional sperm • Ex: mammals - cortical granules release enzymes  modify egg cell receptors  prevent binding by additional sperm.

16. Cleavage • Cleavage - set of rapid cell divisions in animal zygotes immediately after fertilization. • 1ststep is embryogenesis - process that makes single-celled zygote into multicellular embryo. • partitions egg cytoplasm without additional growth of the zygote. • Cells created by cleavage divisions called blastomeres. • Completed cleavage results in embryo consisting of mass of blastomere cells called a blastula.

18. Gastrulation • Gastrulation- extensive & highly organized cell movements radically rearrange embryonic cells into structure called the gastrula. • results in formation of embryonic tissue layers (**tissue is integrated set of cells functioning as a unit) • most embryos have 3 primary tissue layers: ectoderm, mesoderm, and endoderm. • these tissues are called germlayers because they give rise to adult tissues and organs.

19. Ectoderm - forms outer covering of adult body & nervous system • Mesoderm - gives rise to muscle, most internal organs, & connective tissues like bone & cartilage • Endoderm - produces lining of digestive tract or gut, along with some associated organs

21. What if something goes wrong?What happens then???

22. nondisjunction - chromosomes do not segregate correctly during meiosis • Incorrect chromosome # • Deletion • Duplication • Inversion • Translocation ** Extra chromosomes often means survival** **Missing chromosomes often means DEATH**

23. Monosomy - One less chromosome due to missing chromosome in gameteEx: Turner Syndrome KARYOTYPE

24. Trisomy- Gamete has an extra chromosome • Ex: Trisomy 21 (Down Syndrome)

25. Polyploidy -CompleteEXTRA sets of chromosomes • almost ALWAYS lethal to animals • plants can be healthier & larger

26. Genetic testing • Amniocentesis in 2nd trimester • sample of embryo cells • stain & photograph chromosomes • Analysis of karyotype

27. Sex chromosomes abnormalities • Human development more tolerant of wrong numbers in sex chromosomes • Results in variety of distinct syndromes • XXY = Klinefelter’s syndrome male • XXX = Trisomy X female • XYY = Jacob’s syndrome male • XO = Turner syndrome female