Genes & Development
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Transcript 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
Boveri’s support for nuclear control
Polyspermy in sea urchins
• Embryos developing with multiple sets of
chromosomes had defects
• Chromosome number (nucleus) important
Gene Theory
EB Wilson & Nettie Stevens
Correlated chromosome absence/presence with
sex determination
• Drosophila
XO & XY = male
XX = female
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
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
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!
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
Geneticists vs Embryologists
Embryologists set forth 3 criteria that must be
satisfied by genetics in order to accept the
dominance of the gene theory
1. How can identical chromosomes give rise to
differentiated cell types
2. Demonstrate that genes control early
developmental processes
3. Explain environmentally influenced phenomena
such as temperature dependent sex
determination
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
Gene Action in Early Development
Drosophila wing mutations
Conrad Waddington
Demonstrated defects in the imaginal disk
formation
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
Genomic Equivalence
Explain differential gene expression
1. Establish that genomes of differentiated
cells are equivalent
2. Determine why only certain genes are
expressed
Genomic Equivalence
Regeneration of newt lens
Remove lens
Iris cells trans-differentiate to regenerate the
lens
Series of changes in iris cells
1.
2.
3.
4.
5.
6.
Ribosome synthesis
DNA replication
mitosis
exocytose melanosomes
form a group of undifferentiated cells
turn on crystalline genes
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
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
Genomic
Equivalence
Procedure for cloning frogs
from differentiated nuclei.
Successful cloning requires
serial passage of donor
nuclei through activated
oocytes.
Genomic Equivalence
Enucleate oocyte
Isolate donor nuclei
Inject nuclei into oocyte
Genomic Equivalence
Totipotency of donor
nuclei appears to
decline with age
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%)
Genomic Equivalence
Cloned Mice