Glossary of Chapter 8 - Principles of Development
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- What was the main belief of preformation?
- a miniature adult is present in the sperm or egg, waiting to unfold
- In epigenesis, what two facts are known about the embryo?
- it is a new creation that develops and differentiates in a step by step manner and it has new parts produced in it that were not in the zygote
- What is the main belief in the hierarchy of developmental decisions?
- life begins with the zygote and progresses by dividing mitotically
- What are the 6 stages of development in order?
- 1) gamete formation
- What occurs in gamete formation?
- the sperm and eggs form and mature
- What occurs in fertilization?
- the egg and sperm fuse
- What occurs in cleavage?
- th zygote subdivides and determinants are partitioned in blastomeres
- What occurs in gastrulation?
- germ layers form
- What occurs in organogenesis?
- body organs form and cells interact and differentiate
- What occurs in the growth stage of development?
- organs increase in size and the adult body form is attained
- What is the effect on the size of the egg during oocyte maturation?
- the egg increases in size
- What does the egg cytoplasm contain and what are these products required for?
- mRNA, ribosomes, and tRNA; required for protein synthesis
- What is the purpose of the morphogenetic determinants?
- they direct early development
- Where are the morphogenetic determinants located?
- in the egg cytoplasm
- What are the two functions of metabolic inhibitors?
- 1) maintain egg in a quiescent state
2) inhibit translation of mRNA
- What stage is the egg in when it is first formed?
- Prophase I of Meiosis I
- What must occur for Meiosis II to be completed?
- the egg must be fertilized
- What is fertilization?
- the union of egg and sperm that restores the diploid chromosome number
- How does fertilization activate egg development?
- by removing the metabolic inhibitors
- What do many marine eggs release to attract sperm of the same species?
- a chemotactic molecule
- What is the path of sea urchin sperm?
- through the jelly layer and then through the vitelline envelope
- What do the egg-recognition proteins on sperm bind to?
- species-specific sperm receptors on the V.E.
- What occurs when the sperm binds to the V.E.?
- a fertilization cone appears
- What occurs after the fertilization cone appears?
- a "fast block" prevents the entrance of additional sperm
- What is the "fast block"?
- an electrical potential that spreads over the membrane
- What follows the "fast block"?
- a cortical reaction
- What 4 events occur during the cortical reaction?
- 1) granules in the egg cortex fuse with the plasma membrane
2) the granules release enzymes between the plasma membrane and V.E.
3) the V.E. is lifted away
4) the V.E. hardens, becoming the fertilization membrane
- What occurs after the cortical reaction?
- the male and female pronuclei fuse
- What does the fusion of the pronuclei remove?
- the metabolic inhibitors
- What occurs in the egg following removal of the metabolic inhibitors?
- a burst of DNA and protein synthesis
- What is the protein synthesis in eggs directed by?
- maternal mRNA stored in the cytoplasm
- What does fertilization initiate?
- reorganization of cytoplasm
- What does fertilization reposition?
- determinants that begin development and cleavage
- What is cleavage?
- a series of early mitotic cell division
- What increases in cleavage?
- the number of cells
- What doesn't increase in cleavage?
- the size of the organism
- What does the size of the organism not exceed?
- the size of the zygote
- What are produced during cleavage?
- the blastomeres
- What two factors determine the pattern of cleavage?
- 1) the quantity and distribution of yolk present
2) genes controlling the symmetry of cleavage
- What are two characteristics of isolecithal eggs?
- 1) very little yolk
2) yolk evenly distributed in cytoplasm
- What are 3 examples of animals with isolecithal eggs?
- echinoderms, molluscs, and mammals
- What are two characteristics of mesolecithal eggs?
- 1) moderate amount of yolk
2) yolk concentrated in the vegetal pole
- What is an example of animals who have mesolecithal eggs?
- What are two characteristics of telolecithal eggs?
- 1) large amount of yolk
2) yolk concentrated at the vegetal pole
- What are 4 examples of animals who have telolecithal eggs?
- birds, reptiles, most fish, few amphibians
- What are two qualities of holoblastic cleavage?
- 1) it occurs in isolecithal and mesolecithal eggs
2) the cleavage furrow extends completely through the egg
- What are three qualities of meroblastic cleavage?
- 1) it occurs in telolecithal eggs
2) the cleavage furrow doesn't cut through the heavy yolk in the vegetal pole
3) division is confined to a narrow disc-shaped mass on the yolk
- What are the 4 major cleavage patterns of isolecithal eggs?
- radial, spiral, bilateral, and rotational
- In radial cleavage, what does the first series of cleavage divisions produce?
- lightly touching blastomeres stacked on top of each other
- What can occur if the blastomeres produced in radial cleavage separate?
- each blastomere can direct its own development into a normal embryo
- Which type of development occurs in radial cleavage?
- regulative development
- What is the position of the cleavage planes in spiral cleavage?
- oblique to the animal-vegetal axis
- Where are the cells tiers that are produced in spiral cleavage located?
- in the cleavage furrows of existing cells
- What two actions can occur if the cell tiers are separated in spiral cleavage?
- development stops or abnormal embryos are produced because blastomeres aren't capable of directing own development
- Which type of development occurs in spiral cleavage?
- mosaic development
- In which organisms does bilateral cleavage occur?
- tunicates (sea squirts)
- In bilateral cleavage, what is determined before fertilization and why?
- the anterior-posterior axis; because of unequal distribution of cytoplasmic components
- In which organisms does rotational cleavage occur?
- Where does the 1st rotational cleavage plane cut through?
- the animal/vegetal axis
- What occurs in the 2nd rotational cleavage plane?
- one blastomere divides meridianally while the other divides equatorially
- What is the product of rotational cleavage?
- an odd number of cells
- What is a blastula?
- a hollow ball of cells produced by cleavage divisions
- In mammals, what is the blastula called?
- a blastocyst
- What is gastrulation?
- the conversion of blastula into a gastrula, a complex structure with 3 tissue layers
- What occurs with the blastomeres in gastrulation?
- they migrate to positions to establish the embryonic body plan
- What is the coelom?
- a true body cavity lined by mesoderm
- What does the mesoderm contain?
- the viscera
- What are the two types of coelom formation?
- schizocoelous and enterocoelous
- What does the coelom form from in schizocoelous formation?
- the splitting of the mesoderm
- What does the coelom form from in enterocoelous formation?
- outpockets of the archenteron
- Which tissue layer is the nervous system derived from?
- What are the three primary tissue layers?
- ectoderm, endoderm, and mesoderm
- What are three functions of the coelom?
- 1) provides a tube within a tube arrangement
2) permits greater size and complexity
3) provides space for specialization of organs
- What is the Roux-Weismann hypothesis?
- nuclear division "breaks up" the genome into smaller units which are parceled out to cells; each cell only receives the genetic information for its characteristics
- Who disproved the Roux-Weismann hypthesis?
- Hans Spemann
- What two results were obtained from Spemann's experiments?
- 1) all cells contain the same genetic information
2) cytoplasm in the area of the gray crescent contains info essential for normal development
- How are cytoplasmatic components distributed in a zygote?
- What determines the cell fate?
- morphogenetic determinants
- What does yellow cytoplasm form?
- muscle cells
- What does gray equatorial cytoplasm form?
- notochord and neural tube cells
- What does clear cytoplasm form?
- larval epidermis cells
- What does gray vegetal cytoplasm form?
- gut cells
- What is embryonic induction?
- the capacity of some cells to evoke a specific developmental response in others
- What does primary induction set in motion?
- secondary inductions
- What three events does the induction sequence include?
- 1) cell movement
2) changes in adhesion
3) cell proliferation
- How is protein synthesis controlled during development?
- from cleavage to mid-blastula stage--controlled by maternal mRNA
afterward--controlled by zygote
- Which three types of organisms do amniotes include?
- birds, reptiles, and mammals
- What did the evolution of the shelled amniotic egg make a requirement?
- internal fertilization
- What are the two functions of the amnion?
- surrounds embryo/fetus and secretes amniotic fluid
- Which extraembryonic membrane of the shelled amniotic egg pre-dates amniotes by millions of years?
- the yolk sac
- What are the two functions of the allantosis?
- storing metabolic wastes and serving as a respiratory surface
- Which structure encloses all of the other extraembryonic membranes?
- the chorion
- Where is the chorion located?
- beneath the egg shell
- What does the chorion act as?
- a respiratory surface for gas exchange
- What does the chorioallantoic membrane serve as?
- a respiratory surface
- What are monotremes?
- primitive mammals that lay eggs
- What are the two monotremic animals?
- the spiny anteater and the duck-billed platypus
- How do marsupial embryos develop?
- they develop in the uterus, but dont' implant in the uterus; embryos emerge from the uterus and finish developing in an external pouch
- In placental mammals, where do the young develop?
- in the uterus
- What modifications have occurred in the amnion?
- What modification has been made to the chorion?
- it now has a maternal contribution to the placenta
- What modification has been made to the allantosis in placental mammals?
- it contributes to the formation of the umbilical cord
- What modification has been made to the yolk sac in placental mammals?
- it doesn't contain yolk, but it serves as a source of stem cells that give rise to blood and lymphoid cells
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