Biol 4033 Lecture 2

"New Genes Are Generated From Existing Genes." Antievolution argument: adding one amino acid at a time to growing chains would take too long.

4 models of genetic innovation: Intragenic mutation, gene duplication, DNA segment shuffling(domains), horizontal transfer.

Homologous genes: (two ways to give rise to gene families)

Orthologs: ancestral gene diverges in separate species

Paralogs: ancestral gene diverges in single organism

Viruses carry genetic info.: transduction. Horizontal transfer between species much more common in prokaryotes 18% of E. coli genome horizontally transferred within 100 million years (strains dissimilar).

Eucaryotes resemble archaea for DNA replication, transcription, and translation; more like eubacteria for metabolic processes. (DNA from 3 pools of promiscuous primordial communities?)

DNA sequencing: only 16% of Mycobacterium tuberculosis' 4,000 genes = totally unfamiliar. Lipid molecule synthesis emphasized in genome.(basis for acid fast stain). Resist immune assault?

M. tuberculosis discussion interesting. Mycollic acid layer = water repellant (surfactants needed in medium). Many genes devoted to lipid metabolism.

Eucaryotic sex = horizontal transfer. Vertical transfer = parent to progeny.

Viral transfers (transduction) specialized or generalized. Mimic processes that go on within cells (plasmids, transposons, etc.).

Mutations revealing gene functions:

Loss of function. Temp-sensitive mutations. Accumulation of metabolic intermediates. Domain swapping. Systematic alteration of a.a. sequences.

Endosymbiont hypothesis (Lynne Marguilis). How does DNA transfer from "bacterium-like" endosymbiont to main chromosome?

Paul Berg and "junk DNA" wager. Why do puffer fish have so little "junk" DNA? Prokaryotes: "wall-to-wall exons".

Model organisms: Escherichia coli, Saccharomyces cerevisiae, Arabidopsis thaliana, Caenorhabditis elegans, Drosophila melanogaster.