1. Mendel’s work and the genes
Eörs Szathmáry (Alpbach 2005)
Collegium Budapest
Eötvös University Budapest

2. Concepts of inheritance
J.B.S. Haldane:
„I inherited my watch from my father”
„I inherited my nose from father”
Geneticists are interested in the latter
„Genetics deals with the question why organisms that look almost alike are nevertheless different, in a hereditary fashion”

3. The man and the garden

4. The plant and the work

5. Traits chosen by Mendel

6. Prevention of self-fertilization

7. Mendelian inheritance
Gametes are always clean!
Stoichiometric paradigm
Probabilistic combinations

8. Segregation of dominant mutation
½ of the offsping in F2 generation shows dominant phenotype

9. Segregation of recessive mutation
Recessive phenotype appears in 1:3 proportion in generation F2

10. Two traits together
A concrete count of two segregating traits

11. Two segregating traits
No linkage
Punnett’s table
Independent combination

12. Mendel was extremely lucky that his traits are on different chromosomes
Some deviations from Mendel’s rules could not be reconciled in any other way than assuming that they are linked together as “beads on a string”
Morgan has made crosses to analyse linkage
The concept of recombination was later linked to the cytological observation of meiosis (reductive cell division)

13. The cytology of meiosis

14. How meiosis is integrated into the plant life cycle

15. The molecular mechanism of recombination

16. Whether recombination really occurs depends on the way the Holliday junction is resolved

17. Whereas genetic recombination can generate variation, its evolutionary role is unclear
Genetic recombination can generate good chromosomes out of partially bad ones
But, unfortunately, the opposite is also true
Something must generate an asymmetry because recombination is “costly”

18. The compementarity principle

19. The principle of DNA copying

20. Genes tend to specify the structure of a protein
Nucleotides sequence of DNA specifies the amino acid sequence of proteins
Proteins can be structural components or enyzmes
“Information: the precise determination of sequence” (Francis Crick)

21. This shows the genetic code

22. The genetic code is remarkable

23. The simplest cells are bacterial

24. Eukaryotic cells are very complex

25. Bacterial genes are much simpler than eukaryotic ones

26. A vast variety of gene products are generated by alternative splicing