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Berthold’s Experiment: Introduction
• Background: pangenesis/preformation theory
of reproduction
– Idea that various body parts secreted bits of
themselves into the blood and these assembled in
semen. Preformation extends this to teeny animals
(homunculi) being formed in sperm in the testes.
These homunculi then simply grew larger to form
babies.
• Not a very promising start, but it had some
truth that helped Berthold:
– Body parts able to secrete factors into blood
– These factors have targets distant to origin
– The testes were somehow involved in this
Berthold’s Hypothesis
• According to pangenesis/preformation, bits of
organs travel through the blood stream to the
testes to make a copy of that animal. This theory
makes a specific prediction that seems testable:
Hypothesis: transplanted testes should pass on
the properties of host and not the donor to
offspring…
(N.B. this is my guess as to why Berthold did his
experiment, we don’t really know why)
Berthold’s Experiment: Methods
• Experimental design:
– control group 1: castrated only
Concern: What are effects of castration on roosters?
– control group 2: castrated and testes reimplanted
Concern: Will testes be functional after removal and
implantation?
– experimental group: castrated and cross- implanted
Will testes function like the host (support pangenesis) or
like the donor (refute pangenesis).
Unfortunately for our imagined hypothesis, implanted roosters
aren’t fertile. So we get no further towards disproving pangenesis.
BUT…
serendipity!
TARGET PROBE
LABEL
IN SITU IN VITRO
Hormone
(nonprotein)
Antibody
Isotope
Enzyme
Protein
Antibody
RNA
cDNA
Isotope
ISH
Enzyme
Fluorophore
Northern
RT-PCR
microarray
DNA
cDNA
Isotope
Not
common
Enzyme
Fluorophore
Southern
PCR
RFLP
Not
RIA
Common EIA/ELISA
Enzyme
Assays
Isotope
IHC
Western
Enzyme
(not
Fluorophore ICC!)
Microarrays
• Relatively new technology.
• Different kinds, idea is that the expression of
1000s of genes can be determined at once
using an array of very small dots, each of a
specific cDNA
• This kind of “high throughput” sampling of gene
expression is very fashionable
Benefit: lots of information fast
Cost: expensive, validation and analysis is
laborious, often inconclusive (fishing expedition)
Genetically modified organisms
• Transgenesis (designer genes)
Artificial genes that are added to
genome
• Gene Targeting (knock-outs/ knockins)
Artificial genes that replace genomic
sequences
Benefit: very powerful way of testing
gene function
Cost: laborious & time intensive,
abnormal genetic makeup often
complicates study
Temporary genetic manipulations
• Antibody binding can be used to interfere with
protein function as well as for detection
• RNAi = RNA interference (a.k.a. antisense). cRNA
or cDNA can reduce protein abundance of specific
genes
• Transfection (a.k.a. gene therapy). Introduction of
foreign genes into cells using vectors (eg viruses)
Benefits: less time-intensive than GMOs, can also
overcome developmental and compensatory
effects often seen in GMOs
Costs: transient, variable, inefficient