1. Aim: How does an embryo develop inside the uterus?

2. How does the zygote form? Zygote – A fertilized egg

3. What happens after fertilization? The zygote begins to divide and travels to the uterus, eventually implanting itself in the uterus lining

4. What happens to the zygote after it is formed? Mitosis – causes the zygote to repeatedly divide producing the developing embryo.

5. Embryonic Development: + Sperm Egg Fertilization Zygote Mitosis Embryo- the stage in human development from the first division of the zygote until about nine weeks after fertilization.

6. Cleavage The term used to describe the early cell division associated with embryonic development. During this time period, the number of cells increase tremendously.

7. EARLY DEVELOPMENT Cleavage occurs by mitosis 4 days = 50 cells 6-7 days = 100 cells and…. Attaches to the uterine wall (IMPLANTATION)

8. The result of cleavage is an embryo that is ….. A solid ball of cells which moves towards the uterus Morula Not referring to size

9. TWINS Fraternal Twins Two eggs were released and both fertilized by different sperm. Not genetically identical Identical Twins One egg fertilized by one sperm. The embryo split for some reason around the morula stage

10. Mitosis continues & the embryo becomes…… A hollow ball of cells Blastocyst Not a reference to size

11. Gastrula fold inwardly, creating layers to the embryo’s shape Cell division continues & the cells of the embryo start to ….

12. Gastrulation Three layers Each layer will eventually form the different organ systems Ectoderm (skin & CNS) Endoderm (GI Tract & lungs) Mesoderm (muscle, bone, blood)

13. CELL DIFFERENTIATION Due to gene expression, cells undergo cellular differentiation, in which the cells become increasingly specialized in structure & function.

14. Gene Expression All genes of the genome are present in every cell of the body, but only a small, specific fraction of these genes are actually expressed in each type of cell. Genes that are being expressed are turned “on”

15. What makes some cells turn “on” some genes while other genes are “off”? Environmental influences from within the cell, from surrounding cells, or from outside the organism.

16. Why are they different? These seeds carry the same genes for chlorophyll: CC Grown in light Grown in dark “ENVIRONMENT AFFECTS GENE EXPRESSION”

17. Differentiation’s ultimate goal… An embryo with many different types of cells

18. Stem Cells Stem cells are embryonic cells that can turn into any type of cell in the body

19. How can stem cells help us? Can be used to make any type of cell that needs to be replaced in our bodies

20. Why is the use of stem cells so controversial? They are often taken from fetuses. Opponents believe that you are killing a life.

21. Are stem cells only embryonic? No, there are some adult stem cells, but they don’t have the potential to become every kind of cell