10-26-11 Genes and Development II

10-26-11 Genes and Development II - ZOL 320 Developmental...

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ZOL 320 Developmental Bio October 26, 2011 Genes and Development II Major Questions: When do cells lose totipotency? When do nuclei lose totipotency? (And are any epigenetic changes reversible?) How can we determine a developmental gene’s function? I. Cellular totipotency – when do cells lose totipotency in development? A. Blastomere isolation experiments: a. If a cell can give rise to completely embryo, then that cell is fully totipotent, like a zygote b. Look at results using: b.i. Individual blastomeres, then b.ii. Blastomeres in groups, then b.iii. Individual blastomeres put in a group c. 1 & 2 are used to assess whether development is determinate or indeterminate. d. For comparison: A mature plant differentiated cell is totipotent d.i. 1 phloem cell callus d.ii. With experimental help, phloem cells are capable of reforming entire plant e. Only the zygote is totipotent during determinant development of tunicate (mosaic development) f. 1 st Question: When does determined blastomere lose totipotency? f.i. Sea urchin cells up to 4 cell stage = totipotent f.ii. Summary results of animal blastomere isolation experiments: Animal Stage at which totipotency is lost Tunicate Zygote Sea urchin 4 cell stage Frog 4 cell stage (only 2 with grey crescent) Mouse 8 cell stage f.ii.1. Main point: Individual cells lose totipotency quickly in both determinant and indeterminate embryos.
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