GENETIC CONTROL OF PATTERN FORMATION
1993 Woodrow Wilson Biology Institute
HIGHLIGHTS OF DR. ERIC WIECHSHAUS LECTURE
The history of the use of Drosophila in scientific research is based upon the unique value of the organism to science and the scientist at the right historical moment.
All of the basic genetics questions were worked out. The concept of genes, recombination, gene mapping, linear genes, cytology, sex determination and sex linkage could all be shown from experiments with drosophila.
It was discovered that mutations could be induced. This shifted the emphasis to the use of E. coli and yeast as they were the organisms of value to the molecular biologist.
DNA was identified; DNA-RNA-Proteins synthesis was worked out; the genetic code was identified. DNA was determined to be the repository of information. Jacob and Monod did work on the Lac operon and the control of gene expression. This lead to the application of genetics to other biological processes.
Genetics was applied to embryonic development and the fruit fly again became a strategic organism. The single celled organisms could not show influence on genetic development as clearly as the developing embryo.
In the 1970's
Molecular biologists estimated the number of genes by the quantity of DNA extracted from organisms
Sea Urchin 8 X 108 4 X 105 # of genes
Gene Estimates Drosophila 1.2 X 108 .6 X 105
These calculations depend on the figures that 400-2000 amino acids make one protein. From this work it was believed that there were 100 to 150,000 genes in Drosophila.
Judd performed experiments to determine what happened when genes were destroyed. He worked on an area of the X chromosome (0.3 % of the genome) and determined which homologous organisms did not survive embryonic development. Using complementation tests, 112 different mutations that broke down into 15 groups were determined.
From these experiments he determined that there were only 5,000 genes. This was the first estimate of the number of genes by a geneticist. The molecular biologists did not accept this number at first.
Then Dr. Wiechshaus set up a study of 20,000 lethal mutations to Drosophila to determine how many were lethal in the embryo. 20-25% died, of which many looked normal, 539 showed a visible change in the embryo. He did complementation tests on these genes and determined that there were 139 sets of genes responsible for embryonic development.
The essential problem was that there are two sources of genetic products in the embryo.
- Some proteins come from the mother, stored in the egg.
- Some are made by the embryo.
So it was necessary to isolate only those which were produced by the embryo. Even though most proteins were from the mother (actin/mycin, RNA Polymerase, and ribosomes for example), the embryo produces specific proteins for gene expression and cell specialization that are not from the mother because certain cells must have specific proteins for gene expression, specialization. Some proteins are the same in all cells: actin/mycin, RNA polymerase, and ribosome protein. This discovery showed the relationship between genetics, gene expression and embryological development. The work apples to mammals because they have many of the same proteins! But more proteins are supplied by the embryo because it develops for nine months.