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Genes & Development

Genes & Development. Part 1: The Debate. Gene Theory. Nuclear vs Cytoplasmic Inheritance Is control over development tied to the nucleus (chromatin) or to the cytoplasm? T Boveri & EB Wilson – Nuclear control TH Morgan – cytoplasmic control. Gene Theory.

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Genes & Development

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  1. Genes & Development Part 1: The Debate

  2. Gene Theory • Nuclear vs Cytoplasmic Inheritance • Is control over development tied to the nucleus (chromatin) or to the cytoplasm? • T Boveri & EB Wilson – Nuclear control • TH Morgan – cytoplasmic control

  3. Gene Theory • Boveri’s support for nuclear control • Polyspermy in sea urchins • Embryos developing with multiple sets of chromosomes had defects • Chromosome number (nucleus) important

  4. Gene Theory • EB Wilson & Nettie Stevens • Correlated chromosome absence/presence with sex determination • Drosophila XO & XY = male • XX = female

  5. Gene Theory • TH Morgan • Chief proponent of cytoplasmic inheritance • 1910 his lab accumulated data that supported chromosomal inheritance • Discovered and characterized Drosophila white (w) mutant (has white eye) • w phenotype had sex linked inheritance pattern – • w male x wt female  F1 all wt offspring • wt male x F1 female  only w-eyed males

  6. Gene Theory • Morgan’s conversion • Since mutation was inherited together with the X chromosome, Morgan accepted the chromosomal inheritance theory wholeheartedly • Went further to hypothesize that genes were arranged linearly on chromosomes

  7. Gene Theory • Nettie Stevens was a graduate student with Morgan at Columbia University • Did postdoctoral studies with Wilson • Wilson and Morgan were very good friends • HOMEWORK: go online to devbio website and read material at website 4.1 Quiz on Monday!

  8. Geneticist vs Embryologist • Wilson and Morgan were embryologists • Their combined support of the chromosomal inheritance theory brought more geneticists into embryological systems • Influx of geneticists was disdained by classical embryologists • EE Just, H Spemann, F Lillie et al

  9. Geneticists vs Embryologists • Embryologists set forth 3 criteria that must be satisfied by genetics in order to accept the dominance of the gene theory • How can identical chromosomes give rise to differentiated cell types • Demonstrate that genes control early developmental processes • Explain environmentally influenced phenomena such as temperature dependent sex determination

  10. Gene Action in Early Development • Brachyury (brachy = short; ury = tail) • Salome Gluecksohn-Schoenheimer • Characterized the early embryos of mice with the Bra mutant • Adult phenotype – deformed tails/pelvis • Embryo phenotype – lack posterior notochord

  11. Gene Action in Early Development • Drosophila wing mutations • Conrad Waddington • Demonstrated defects in the imaginal disk formation

  12. Gene Action in Early Development • Both Waddington’s and Gluecksohn’s experiments established that genes did effect early developmental processes • 1 down 2 to go

  13. Genomic Equivalence • Explain differential gene expression • Establish that genomes of differentiated cells are equivalent • Determine why only certain genes are expressed

  14. Genomic Equivalence • Regeneration of newt lens • Remove lens • Iris cells trans-differentiate to regenerate the lens • Series of changes in iris cells • Ribosome synthesis • DNA replication • mitosis • exocytose melanosomes • form a group of undifferentiated cells • turn on crystalline genes

  15. Genomic Equivalence • Cloning – the ultimate equivalence test • Generate an entire, normal animal from a the nucleus of a somatic cell • Requires that somatic nucleus is totipotent

  16. Genomic Equivalence Cloning of the frog Xenopus laevis by nuclear transplantation of albino gut cell nuclei into enucleated, wt oocytes. All progeny are albino & female

  17. Genomic Equivalence Procedure for cloning frogs from differentiated nuclei. Successful cloning requires serial passage of donor nuclei through activated oocytes.

  18. Genomic Equivalence Enucleate oocyte Isolate donor nuclei Inject nuclei into oocyte

  19. Genomic Equivalence Totipotency of donor nuclei appears to decline with age

  20. Genomic Equivalence • Dolly • 1st cloned mammal • Mammary epithelial cell • Cultured and maintained in G0 • Fused with enucleated oocyte by electric shock • 1/434 success rate (0.23%)

  21. Genomic Equivalence Cloned Mice

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