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Development

Development. Introduction Early Stages of Development Quiz part 1 Suites of Developmental Characters Quiz part 2. In this tutorial, you will learn:. The basics of early development from fertilization through gastrulation. Major differences in early development between taxonomic groups.

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Development

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  1. Development Introduction Early Stages of Development Quiz part 1 Suites of Developmental Characters Quiz part 2

  2. In this tutorial, you will learn: • The basics of early development from fertilization through gastrulation. • Major differences in early development between taxonomic groups. Credits: Figures and images by N. Wheat unless otherwise noted. Starfish embryo photos courtesy of K. Wynne. Blastocyst image from Wikipedia. Funded by Title V-STEM grant P031S090007.

  3. Introduction • Development describes the changes in an organism from its earliest beginnings through maturity.

  4. Fertilization Fertilization is the initial event in development in sexual reproduction. Union of male and female gametes. Recombination of paternal and maternal genes. Restoration of the diploidnumber (two sets of chromosomes).

  5. Zygote • The diploid cell resulting from fertilization is now called a zygote. • Photos in the following slides illustrate development in the starfish (Phylum Echinodermata). Photo courtesy of K. Wynne

  6. Cleavage • Cleavage – rapid cell divisions following fertilization. • Very little growth occurs while the cells are dividing. • Each cell called a blastomere. • Video of cleavage stages in a frog. 4 cell stage 2 cell stage Photos courtesy of K. Wynne

  7. Morula • Morula – the name given to the solid ball of cells that results from cleavage. • First 5-7 divisions. Photo courtesy of K. Wynne

  8. Blastula • As divisions continue, a fluid filled cavity, the blastocoel, forms within the embryo. • The resulting hollow ball of cells is now called a blastula. late blastula early blastula Photos courtesy of K. Wynne

  9. Gastrulation • The morphogenetic process called gastrulation rearranges the cells of a blastula into a three-layered (triploblastic) embryo, called a gastrula, that has a primitive gut (archenteron). early gastrula late gastrula Photos courtesy of K. Wynne

  10. The Blastopore • The blastoporeis the first opening in the embryo – the point of invagination during gastrulation. • The blastopore will eventually become either the mouth or the anus. • One end of the gut-tube or the other. • The space that forms during this time is the primitive gut, the archenteron. Blastopore Archenteron Photo courtesy of K. Wynne

  11. Germ Layers • The three tissue layers produced by gastrulation are called embryonic germlayers. • The ectodermforms the outer layer of the gastrula. • Outer surfaces, neural tissue • The endoderm lines the embryonic digestive tract. • The mesodermpartly fills the space between the endoderm and ectoderm. • Muscles, reproductive system

  12. Gastrulation – Sea Urchin • Gastrulation in a sea urchin produces an embryo with a primitive gut (archenteron) and three germ layers. • Video of sea urchin gastrulation.

  13. Gastrulation - Frog • Result is again an embryo with gut & 3 germ layers. • Gastrulation in the frog is more complicated due to the moderate amount of yolk present in the egg. • Blastula wall more than one cell thick. • Video of gastrulation in a frog.

  14. Gastrulation - Chick • Gastrulation in the chick is affected by the large amounts of yolk in the egg. • Embryo essentially sits on top of large mass of yolk. • Primitive streak – a groove on the surface along the future anterior-posterior axis. • Functionally equivalent to blastopore lip in frog. • Video of Gastrulation in a chick.

  15. Gastrulation - Mammal • In mammals the blastula is called a blastocyst. • Inner cell mass will become the embryo while trophoblast becomes part of the placenta. Inner cell mass Trophoblast

  16. Gastrulation – Mammal (2) • Gastrulation in mammals involves the inner cell mass and is similar to that of the chick due to the fact that mammalian ancestors and early mammals laid eggs. • The large mass of yolk may be gone, but the developmental pattern remains.

  17. Question 1 Shortly after fertilization, the zygote undergoes a series of rapid cell divisions. This is called • Meiosis • Gastrulation • Organogenesis • Cleavage

  18. Question 1 Sorry! • That is incorrect. • Try again!

  19. Question 1 Congratulations! • You are correct!

  20. Question 2 During cleavage, each cell in the embryo is called a • Blastula • Morula • Gastrula • Blastomere

  21. Question 2 Sorry! • That is incorrect. • Try again!

  22. Question 2 Congratulations! • You are correct!

  23. Question 3 The solid ball of cells that results from cleavage is called • Blastula • Morula • Gastrula • Blastomere

  24. Question 3 Sorry! • That is incorrect. • Try again!

  25. Question 3 Congratulations! • You are correct!

  26. Question 4 A fluid filled space called the blastocoel forms inside the embryo - at this point it is a • Blastula • Morula • Gastrula • Blastomere

  27. Question 4 Sorry! • That is incorrect. • Try again!

  28. Question 4 Congratulations! • You are correct!

  29. Question 5 The stage that results in three germ layers and a primitive gut is the • Blastula • Morula • Gastrula • Blastomere

  30. Question 5 Sorry! • That is incorrect. • Try again!

  31. Question 5 Congratulations! • You are correct!

  32. Question 6 Which of the following is not one of the three primary germ layers formed during gastrulation? • Endoderm • Myoderm • Mesoderm • Ectoderm

  33. Question 6 Sorry! • That is incorrect. • Try again!

  34. Question 6 Congratulations! • You are correct!

  35. Question 7 The difference in gastrulation found in different types of animals is due primarily to • The amount of yolk present • The size of the blastomeres • Development in different species is completely unrelated • None of the above

  36. Question 7 Sorry! • That is incorrect. • Try again!

  37. Question 7 Congratulations! • You are correct!

  38. Suites of Developmental Characters • Two major groups of triploblastic animals: • Protostomes include flatworms, annelids and molluscs. • Deuterostomes include echinoderms and chordates.

  39. Protostomes & Deuterostomes • Protostomes & deuterostomes are differentiated by: • Spiral vs. radial cleavage • Mosaic vs. regulative cleavage • Blastopore becomes mouth vs. anus • Schizocoelous vs. enterocoelous coelom formation.

  40. Spiral vs. Radial Cleavage • Spiral cleavage – occurs in most protostomes. • Some ecdysozoans show radial or superficial (insects) cleavage. • Radialcleavage – is found in most deuterostomes. • Tunicates and mammals have specialized cleavage patterns.

  41. Mosaic vs. Regulative Development • Mosaic development – cell fate is determined by the components of the cytoplasm found in each blastomere. • An isolated blastomere can’t develop. • Protostomes • Regulative development – the fate of a cell depends on its interactions with neighbors, not what piece of cytoplasm it has. • A blastomere isolated early in cleavage is able to from a whole individual (e.g. twins). • Deuterostomes

  42. Fate of the Blastopore • Protostome means “first mouth”. • Blastopore becomes the mouth. • The second opening will become the anus. • Deuterostome means “second mouth”. • The blastopore becomes the anus and the mouth develops as the second opening. Blastopore Photo courtesy of K. Wynne

  43. Coelom Formation • The coelom is a body cavity found in many triploblastic organisms that is completely surrounded by mesoderm. • Not all protostomes have a true coelom. • Pseudocoelomates have a body cavity between mesoderm and endoderm. • Acoelomates have no body cavity at all other than the gut.

  44. Coelom Formation (2) • In protostomes that have a coelom, a mesodermal band of tissue forms before the coelom is formed. • In the process of coelom formation called schizocoely, this mesoderm splits to form a coelom. • In enterocoely, the coelom forms as outpocketing of the gut. • Typical deuterostomes have coeloms that develop by enterocoely. • Vertebrates use a modified version of schizocoely.

  45. Question 8 Radial cleavage is found primarily in which group? • Protostomes • Deuterostomes • Both groups show radial cleavage • Neither group shows radial cleavage

  46. Question 8 Sorry! • That is incorrect. • Try again!

  47. Question 8 Congratulations! • You are correct!

  48. Question 9 This figure shows • Radial cleavage • Spiral cleavage • A four-cell stage embryo • A blastula

  49. Question 9 Sorry! • That is incorrect. • Try again!

  50. Question 9 Congratulations! • You are correct!

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