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 jessicaf@cs.ucla.edu

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

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

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

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

From egg to embryo ?

wildtype bithorax Genotype antennapedia Ed Lewis

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

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

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

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)

Homology

Analogy

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