1. Cleavage of Frog and Chick Eggs Chapter VI

2. 4 Total Development = cleavage, morphogenesis, differentiation, growth 4 Cleavage-immediately after fertilization 4 Two kinds of divisions to convert egg to mass of cells –mitosis and cytokinesis 4 First cleavage in frog egg results in two equal size cells

3. 4 2nd cleavage division in frog is also complete and equal 4 3rd division in frog is complete and unequal. Cells are different sizes 4 After many divisions the animal pole has more and smaller cells 4 Egg yolk has effect on cleavage divisions. Slows them down

4. 4 Blastocoel-internal cavity forms near the animal pole after many cleavage divisions 4 Blastula--The developmental stage when the blastocoel forms 4 Bird eggs--99% of egg is yolk, yolk segregated from the cytoplasm 4 Most of the cytoplasm is in the cytoplasmic cap on top of the yolk

5. 4 Cleavage happens in the cytoplasmic cap 4 Don’t have cleavage in entire egg-- Incomplete 4 The cytoplasmic cap is called the blastoderm 4 Under the blastoderm is a space called the subgerminal space 4 Blastoderm is not a blastula because there is no cavity

6. 4 Cleavage in chicken egg produces a blastoderm located at the animal pole 4 Incomplete cleavage occurs

7. Morphogenesis in Frog and Chick Development Chapter VII

8. Morphogenesis 4 Animals acquire form and structure during this developmental stage 4 Movement of cells to specific locations is characteristic of morphogenesis 4 Organism takes on a specific shape 4 Gastrulation--happens in morphogenesis and results in three germinal layers. 4 Also results in the formation of gastrula

9. 4 Three layers in gastrula are ectoderm, mesoderm and endoderm

10. Frog Gastrulation 4 Begins with the blastula 4 First part of gastrulation is the formation of a blastopore on surface of blastula 4 The cells begin to fold inward 4 Further folding of the blastopore results in a cavity called the archenteron. The future gut 4 Blastopore becomes anus 4 The blastocoel is being displaced

11. 4 Continued morphogenic movements result in enlarging the archenteron, reducing the blastocoel and forming a yolk plug over the blastopore 4 In mature frog gastrula there are three germ layers 4 Ectoderm which are the outer cells, Endoderm which line the archenteron, and mesoderm which is in between endo and ecto

12. 4 Mature gastrula is foundation for more development to occur 4 Doesn’t stop morphogenesis 4 Others follow to form cell masses called primary organ rudiments 4 Neurula-stage where the neural plate develops and forms the neural tube which will develop into the future nerve cord

13. Chick Gastrulation 4 Begins with the blastoderm 4 Forms a new cavity below the blastoderm 4 When cavity is formed its called the blastocoel. 4 The subgerminal space is now called the archenteron or future gut 4 Stage is not yet a gastrula because no germ layers

14. 4 Primitive groove forms on surface of blastoderm due to cells moving into the blastocoel 4 Related to the blastopore in frog development 4 After cells move into the blastocoel there are three distinct germ layers and can now be called the gastrula

15. 4 Continuation of morphogenesis results in the neural plate and development of other primary organ rudiments 4 In both the frog and chick the mature gastrula provides the structural foundation for forming more organs

16. Differentiation in Animal Development Chapter VIII

17. 4 Differentiation--where cells take on specific structures and functions 4 Experiment--Future eye region was transplanted into different areas and a salt water solution. –The regions differentiated into different structures when transplanted –Salt water-did not differentiate

18. 4 Potency-the ability of an embryonic part to develop into different kinds of structures 4 Eye region of frog has many potencies 4 Future eye region of frog was undifferentiated 4 Differentiation of eye depends on its location based on experiment

19. 4 Eye regions in neurula were placed at different locations in a later embryo 4 All developed into an eye 4 Eye region of neurula has only one potency 4 In neurula stage the future eye region has become differentiated and can only form an eye 4 The primary organ rudiment in neurula is more determined than in the gastrula

20. 4 As the embryo ages the number of potencies possible for an area becomes less 4 Morphogenesis continues along with the processes of differentiation and growth

21. Factors Controlling Animal Development Chapter IX

22. Nuclear Factors 4 Experiments are presented that demonstrate possible control mechanisms of the events of animal development 4 Experiment with needle into frog eggs. –With nucleus---no effect on embryo –Without nucleus--abnormal or no embryo 4 Results indicate that nucleus controls embryo development 4 All cells result from mitosis and cytokinesis

23. Cytoplasmic Factors 4 All cells should have the same set of genes 4 They will differentiate into different structures 4 How can they develop differently if they have the same set of instructions? 4 Look at sea urchin development

24. 4 Experiment-pigment band develops into the endoderm of gastrula 4 Egg cut in half through the animal and vegetal. Results animal forms blastula with ectoderm only and dies-Vegetal forms incomplete embryo with all 3 germs layers and dies 4 Results--endoderm and mesoderm formation are contained in the vegetal

25. 4 Exp. 2--Sea urchin cut in half through both animal and vegetal axis-length wise –Forms two small complete embryos 4 Results of both experiments--Germ formation for three germ layers has instructions in the cytoplasm

26. 4 Frog egg experiments-p120 –Hair used to constrict fertilized egg into two halves –Halves connected by bridge of cytoplasm –Gray crescent area of cytoplasm equally divided –Half with nucleus divides first. Both halves form normal embryos

27. 4 2 nd frog experiment. Hair again only constricts with part of grey crescent on one half with nucleus 4 The side with only part of the grey crescent didn’t develop properly while the half with the gray crescent did 4 These experiments indicate that the control of nucleus is regulated by the cytoplasmic environment

28. Extracellular Factors 4 Experiments so far show what happens with unequal distribution of materials within the egg 4 Are there other factors at play in the development of the embryo? 4 In the experiment given on p123 tissue was transplanted into the blastocoel of a gastrula stage embryo

29. 4 From this transplanted tissue a 2 nd head formed where belly tissue should have formed 4 This means that transplanted tissue affects the normal development of tissue 4 Exp. On p125 ectoderm placed in culture = no differentiation on tissues –Ectoderm and mesoderm in culture = differentiation of ectoderm but not mesoderm –Why? Mesoderm stimulated differentiation in ectoderm

30. 4 Induction—name given to process where one tissue induces the differentiation of another 4 This induction can explain how the differentiation of different cells occur at different times. –As new tissue is formed it induces other tissues to form

31. 4 Other experiments indicate that induction is not the only influence on development 4 When a frog gastrula was placed in culture with pieces of adult heart-no normal heart produced in embryo 4 Differentiated adult heart produce certain chemicals into culture that inhibited the development of heart tissue in embryo 4 Inhibition—differentiated cells produce substances that inhibit cells from developing in the same way. Don’t get two hearts this way

32. 4 Interactions occurring between groups of tissues also help development of certain structures –Exp. Limb bud of chick forms when ectoderm and mesoderm work together. –When they are grafted separately they don’t form the limb properly 4 Also has to be limb bud ectoderm and mesoderm. Can’t be any ectoderm and mesoderm 4 Also wing and leg bud experiments performed

33. 4 The mesoderm taken from wing or leg will develop into wing or leg if combined with ectoderm from the other limb 4 Mesoderm controls development of limb but may be affected by kind of ectoderm it is in contact with

34. 4 Differential gene Action—not all genes are turned on at the same time in the cells nucleus 4 Cells differentiate at different rates and in different directions depending on which genes are turned on when

35. The Operon Theory of Gene Control Chapter X

36. 4 How are the genes controlled so that some are on and some are off? 4 Operon Theory—developed with research on bacteria 4 Enzyme-controls rate of chemical reaction 4 Structural genes-control enzymes 4 Operon is operator gene and structural genes

37. 4 Operator gene controls the structural genes 4 Regulatory gene also present to make repressor which deactivates the operator gene and turns of enzyme function of structural genes 4 When enzymes are produced, if high enough concentrations are reached some of them combine with the repressor to trigger the shut off of the operator gene

38. 4 When substrate is high enough it deactivates the repressor and allows the operator gene to turn on the structural genes to function and make enzymes 4 Regulatory gene has indirect effect on the operator gene