1. Background: Molecular Biology ~ Structure of DNA
DNA ~ Coding medium for the instructions set that governs
and propagates living things
Two oppositely oriented strands with sugar-phosphate backbones }
The alpha-helical structure joined by hydrogen bonding
Nitrogenous bases
(“Genetic codes”):
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
Inside of the
nucleus

2. PEPTIDE BIOSYNTHESIS DNA Peptide/protein
= string of amino acids in specific sequence, specified by sequence of nucleotides in the gene (DNA)
mRNA
DNA

3. DNA bases RNA bases RNA Codonsamino acids
A U UUU (phenylalanine)
UUA (leucine)
T A UGG (tryptophan)
C G AUG (start)
UAA (stop)
G C

4. DNARNAPeptide DNA RNA Peptide ……TAC, AAA, AAT, ACC, ATT…..
…..AUG, UUU, UUA, UGG, UAA…..
Peptide
…start phenylalanine--leucine--tryptophan stop

6. “Evo-Devo:” Genes that control development play a major role in evolution

7. From egg to embryo ?

8. wildtype
bithorax
Genotype
antennapedia
Ed Lewis

9. The homeodomain
Homeobox: a conserved stretch of 180 bps found in the genes affected by homeotic mutations
Homeodomain: a 60 aa domain that binds to DNA
Homeobox genes code for the production of transcription factors (peptides) that control downstream gene expression

10. Homeotic mutants Homeotic mutants transform one segment into another
Antennapedia: Leg -> wing
Bithorax Complex: T3 haltere -> T2 wing
Effect segment identity
Found in gene complexes
Order of genes reflects order of segments influenced
Homeotic genes are selector genes selecting identity of entire segment or region

12. Paedomorphosis, Chimpanzee fetus Chimpanzee adult Figure 15.7A, B
Human fetus
Human adult

13. Characters provide basis for classifying
Characters are traditionally phenotypic features (morphology, life cycle, etc.)
But now you can also measure genetic sequences directly
Homologous characters: similarities attributed to shared ancestry (e.g., mammal forelimbs)
Analogous characters: similarities due to convergent evolution (e.g. wings of birds and insects)

14. Homology

15. Analogy

16. Analogy vs homology pitfall
Is a 4-chambered heart an homologous or
analogous character between mammals & birds?
Homologous
Analogous