Exam 3 on Thursday 90% lecture material 10% reading.
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Transcript of Exam 3 on Thursday 90% lecture material 10% reading.
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Exam 3 on Thursday
90% lecture material10% reading
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T F Xenopus animal pole cells grown in isolation make endoderm.
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T F When animal pole cells are cultured with vegetal pole cells, the vegetal pole cells become mesoderm.
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What is the difference between the germ line and a germ layer?
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What are the differences between follicle cells and nurse cells?
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The Drosophila ovary is composed of both somatic follicle cells and germ line nurse cells and oocyte
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Nurse cells synthesize macromolecules and pump them into the oocyte
through the cytoplasmic bridges
oocyte
nurse cells
follicle cells
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Nurse cells are mitotic sisters of the oocyte
Figure 19.4
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dorsal
ventral
anterior posterior
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Molecules synthesized by the nurse cells and specifically localized in the oocyte determine
the anterior/posterior axis of the embryo
Posterior Determinant(nanos)
Anterior Determinant(bicoid)
Oocyte
Specific mRNAs are bound by proteins and transported along microtubules by motor proteins to their destinations
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Ventral follicle cells build a signal into the egg shell that determines the dorsal/ventral axis of the embryo
Ventral follicle cells
Oocyte signals follicle cells,follicle cells signal back to oocytecytoplasm
nucleus
gurken mRNA
PosteriorAnterior
Dorsal
Ventral
torpedo receptor- inhibits pipe
pipe protein
See Fig. 9.11for more details
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Localized maternal mRNAs also influencevertebrate development
Vg1 mRNA
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Vg1 mRNA localizes to the vegetal poleof the Xenopusoocyte
Figure 5.38
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Model for mesoderm induction and organizer formation
Figure 10.26
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C. elegans:
P granulesare segregated at each divisionand make thecell that inherits them the germline
Figure 8.44 cell nuclei P-granules
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The germ line is set aside early in development as a separate cell lineage
This can sometimes be visualized by the segregation of putative "determinants”as in C. elegans
Fertilized egg
"P granule"
mother cell of germline = P4
P1HOW are P-granules segregated?
PAR proteins & microfilaments see p. 246 and Fig. 8.43
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What is the role of the protein Bindin in blocking polyspermy?
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Sperm-eggshell contact triggers the acrosome reaction
Example 1-- the sea urchin
enzymes
Species specificity (equivalent to zona pellucida)
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Mid-blastula transition
and the N/C ratioLets say you have an organism which normally undergoes 4 cell divisions before the MBT
pre-cleavage: N/C ratio = 1/16 = 0.0625 (close to 0)after 4 cell divisions (1 > 2 > 4 > 8 > 16): 16/16 = 1
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Question:
6.) (4 pts, Circle one) In Drosophila, if an embryo is manipulated so that it is now haploid (has ½ the amount of nuclear material), it will undergo one more or one fewer cell division than an embryo with the normal amount of nuclear material. Explain in terms of the N/C ratio. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________
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BlastoporeBlastocoelBlastocystBlastomere
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EARLY CLEAVAGE rapid increase in the number of cells after fertilization
egg contents distributed to cells, often asymmetrically
blastomeres
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hatch from zona pellucida
Fig. 11.27
Fig. 11.25
Development of a Human Embryo From Fertilization to
Implantation
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Two functions of the blastocoel: 1. Prevents cells from interacting too soon2. allows space for cell migrations during gastrulation
animal
vegetal
Early cleavage in Xenopus
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Step 2:Apical constriction and changes in the extracellular matrix create a dome-shaped invagination =archenteron (primitive gut)
blastopore = openingFigure 8.19
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wildtype larva
bicoid mutant
bicoid mutants have no head!!
Figure 9.23
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Fertilization: a multistepprocess
(ECM)
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Sperm-eggshell contact triggers the acrosome reaction
Example 1-- the sea urchin
enzymes
Species specificity (equivalent to zona pellucida)
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attracts/activates sperm
Figure 7.8
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Sperm-eggshell contact triggers the acrosome reaction
Example 2: Mammals
Sperm have ZP3 receptor
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Figure 7.8