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 XO & XY = male XX = female
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