Chapter 38 Reproduction and Development (Sections 38.9 - 38.11)

1. Chapter 38 Reproduction and Development(Sections 38.9 - 38.11)

2. 38.9 Overview of Animal Development • All sexually reproducing animals begin life as a zygote, the diploid cell that forms at fertilization • The same development steps and processes occur in all vertebrates – evidence of their common ancestry

3. 5 Stages of Vertebrate Development • Fertilization • Sperm penetrates an egg, the egg and sperm nuclei fuse, and a zygote forms • Cleavage • Mitotic cell divisions yield a ball of cells (blastula); each cell gets a different bit of the egg cytoplasm • Gastrulation • Cell rearrangements and migrations form a gastrula, an early embryo that has primary tissue layers

4. 5 Stages of Vertebrate Development • Organ formation • Organs form as the result of tissue interactions that cause cells to move, change shape, and commit suicide • Growth and tissue specialization • Organs grow in size, take on mature form, and gradually assume specialized functions

5. Overview: Frog Development

6. transformation to adult nearly complete adult, three years old Sexual reproduction (gamete formation, external fertilization) organ formation tadpole cleavage eggs and sperm larva (tadpole) zygote Fig. 38.13, p. 642

7. transformation to adult nearly complete adult, three years old Sexual reproduction (gamete formation, external fertilization) organ formation eggs and sperm tadpole cleavage larva (tadpole) zygote Overview: Frog Development Stepped Art Fig. 38.13, p. 642

8. Details of Frog Development (1) • Cleavage divides a zygote’s cytoplasm into smaller blastomeres • Number of cells increases, but the zygote’s original volume remains unchanged • cleavage • Mitotic division of an animal cell

9. Details of Frog Development (1)

10. Details of Frog Development (1) gray crescent Here we show the first three divisions of cleavage, a process that carves up a zygote’s cytoplasm. In this species, cleavage results in a blastula, a ball of cells with a fluid-filled cavity. 1 Fig. 38.13.1, p. 643

11. Details of Frog Development (2) • In this species, cleavage results in a blastula, a ball of cells with a fluid-filled cavity (blastocoel) • Tight junctions hold cells of the blastula together • blastula • Hollow ball of cells that forms as a result of cleavage

12. Details of Frog Development (2)

13. Details of Frog Development (2) blastocoel blastula Cleavage is over when the blastula forms. 2 Fig. 38.13.2, p. 643

14. Details of Frog Development (3) • The blastula becomes a three-layered gastrula by the process of gastrulation: Cells at the dorsal lip migrate inward and start rearranging themselves • gastrula • Three-layered developmental stage formed by gastrulation • gastrulation • Cell movements that produce a three-layered gastrula

15. Germ Layers • A gastrula consists of three primary tissue layers (germ layers) • Three germ layers give rise to the same types of tissues and organs in all vertebrates – evidence of a shared ancestry • germ layer • One of three primary layers in an early embryo

16. Three Embryonic Germ Layers • ectoderm • Outermost tissue layer of an animal embryo • endoderm • Innermost tissue layer of an animal embryo • mesoderm • Middle tissue layer of a three-layered animal embryo

17. Details of Frog Development (3)

18. Details of Frog Development (3) ectoderm ectoderm yolk plug neural plate dorsal lip mesoderm future gut cavity endoderm The blastula becomes a three-layered gastrula—a process called gastrulation. At the dorsal lip (a fold of ectoderm above the first opening that appears in the blastula) cells migrate inward and start rearranging themselves. 3 Fig. 38.13.3, p. 643

19. Details of Frog Development (4) • Organs begin to form as a primitive gut cavity opens up • A neural tube, then a notochord and other organs, form from the primary tissue layers • Many organs incorporate tissues derived from more than one germ layer

20. Details of Frog Development (4)

21. Details of Frog Development (4) neural tube notochord gut cavity Organs begin to form as a primitive gut cavity opens up. A neural tube, then a notochord and other organs, form from the primary tissue layers. 4 Fig. 38.13.4, p. 643

22. Details of Frog Development (5) • In frogs, and some other animals, a larva undergoes metamorphosis: a remodeling of tissues into an adult form • The tadpole is a swimming larva with segmented muscles and notochord extending into a tail • During metamorphosis, the frog grows limbs, and the tadpole tail is absorbed

23. Details of Frog Development (5) Tadpole Metamorphosis Sexually mature, four-legged adult frog

24. ANIMATION: Leopard frog life cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

25. 38.10 Early Marching Orders • Egg cytoplasm includes yolk proteins, mRNA transcripts, tRNAs and ribosomes, and other proteins • Some cytoplasmic components are not distributed evenly, but localized in one particular region or another • cytoplasmic localization • Accumulation of different materials in different regions of the egg cytoplasm

26. Cytoplasmic Localization • In a yolk-rich egg, the vegetal pole has most of the yolk and the animal pole has little • In some amphibian eggs, pigment molecules accumulate in the cell cortex, close to the animal pole • After fertilization, a gray crescent forms, where substances essential to development are localized

27. Experiment: Cytoplasmic Localization • At fertilization, cytoplasm shifts, and exposes a gray crescent opposite the sperm’s entry point • First cleavage normally distributes half of the gray crescent to each descendant cell

28. animal pole pigmented Experiment: Cytoplasmic Localization cortex yolk-rich cytoplasm vegetal pole sperm penetrating egg gray crescent fertilized egg A Many amphibian eggs have a dark pigment concentrated in cytoplasm near the animal pole. At fertilization, the cytoplasm shifts, and exposes a gray crescent-shaped region just opposite the sperm’s entry point. The first cleavage normally distributes half of the gray crescent to each descendant cell. Fig. 38.14a, p. 644

29. ANIMATION: Cytoplasmic localization To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

30. Experiment: Cytoplasmic Localization • In one experiment, the first two cells formed by normal cleavage were physically separated from each other • Each cell developed into a normal larva

31. Experiment: Cytoplasmic Localization gray crescent of salamander zygote First cleavage plane; gray crescent split equally. The blastomeres are separated experimentally. Two normal larvae develop from the two blastomeres. B In one experiment, the first two cells formed by normal cleavage were physi-cally separated from each other. Each cell developed into a normal larva. Fig. 38.14b, p. 644

32. Experiment: Cytoplasmic Localization • In another experiment, one descendant cell received all the gray crescent, and developed normally • The other gave rise to an undifferentiated ball of cells

33. Experiment: Cytoplasmic Localization gray crescent of salamander zygote First cleavage plane; gray crescent missed entirely. The blastomeres are separated experimentally. A ball of undifferentiated cells forms. Only one normal larva develops. C In another experiment, a zygote was manipulated so one descendant cell received all the gray crescent. This cell developed normally. The other gave rise to an undifferentiated ball of cells. Fig. 38.14c, p. 644

34. Cleavage: The Start of Multicellularity • During cleavage, a furrow appears on the cell surface and defines the plane of the cut • The plane of division is not random – it dictates what types and proportions of materials a blastomere will get • Each species has a characteristic cleavage pattern

35. From Blastula to Gastrula • At gastrulation, certain cells at the embryo’s surface move inward through an opening on the surface • Cells in the dorsal (upper) lip of the opening are descended from a zygote’s gray crescent • Gastrulation is caused by signals from dorsal lip cells

36. Gastrulation in a Fruit Fly • The opening cells move in through will become the fly’s mouth; descendants of stained cells will form mesoderm

37. Gastrulation in a Fruit Fly Fig. 38.15a, p. 645

38. Gastrulation in a Fruit Fly Fig. 38.15b, p. 645

39. Gastrulation in a Fruit Fly Fig. 38.15c, p. 645

40. Gastrulation in a Fruit Fly Fig. 38.15d, p. 645

41. Experiment: Dorsal Lip Transplant • Dorsal lip of a salamander embryo was transplanted to a different site in another embryo – a second set of body parts started to form

42. Experiment: Dorsal Lip Transplant A Dorsal lip excised from donor embryo, grafted to novel site in another embryo. Fig. 38.16a, p. 645

43. Experiment: Dorsal Lip Transplant B Graft induces a second site of inward migration. Fig. 38.16b, p. 645

44. Dorsal Lip Transplant (cont.) • The embryo develops into a “double” larva, with two heads, two tails, and two bodies joined at the belly

45. Dorsal Lip Transplant (cont.) C The embryo develops into a “double” larva, with two heads, two tails, and two bodies joined at the belly. Fig. 38.16c, p. 645

46. ANIMATION: Embryonic induction To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

47. Specialized Cells, Tissues, and Organs • All cells in an embryo have the same genes • Selective gene expression causes different cell lineages in the embryo to express different subsets of genes • Selective gene expression is the key to cell differentiation – the process by which cell lineages become specialized in composition, structure, and function

48. Cell Differentiation • An adult human has about 200 differentiated cell types • Example: Cells of one lineage turn on genes for crystallin, a transparent protein that forms the lens of the eye – no other cells in the body make crystallin • A differentiated cell still retains the entire genome • It is possible to clone an adult animal (a genetic copy) from one of its differentiated cells

49. Cell Communication in Development • Long-range intercellular signals (morphogens) diffuse out from certain embryonic cells and form a concentration gradient in the embryo that controls differentiation • morphogen • Chemical encoded by a master gene; diffuses out from its source and affects development • Effects on target cells depend on its concentration

50. Cell Communication in Development • Other chemical signals only operate at close range • Example: Cells of a salamander gastrula’s dorsal lip cause adjacent cells to migrate inward and become mesoderm • embryonic induction • Embryonic cells produce signals that alter the behavior of neighboring cells