Lecture #1 - 8/31/01 - Dr. Hirsch

Chapter 1: Evolutionary Framework for Biology

Overall premise: basic similarity in mechanisms between all animals.

Justification for reductionist approach: flies, simple animals.

Text- Fig 1.2: similarity in arm/dog foreleg/ seal flipper

Insect: similarity in basic mechanisms for appendage development

Basic cellular & developmental mechanisms, ie:

Cell death pathways [apotosis]; cell cycle

Segment identity; A/P [anterior/posterior]

D/V [dorsal/ventral] development

Related to: Immune regulation

Lung/tracheal pathways

Eye development; simple vs. compound: link to fly eye structure, development:


Ectopic eyes by ectopic expression of an eye development gene:

Czerny et al Molecular Cell, (1999) Vol. 3, 297307

Neural development & physiology



Complexity in vertebrates: 4x genome duplication vs. flies/worms -> redundant genes

-> common lack of phenotypes in single gene knockouts

Evolutionary Milestones

Earth: ~4.5 billion yrs old: early atmosphere reducing; no O2

First life: ~3.6 billion years ago; origin unclear: simple organic compounds throughout universe.

Precambrian: http://www.ucmp.berkeley.edu/precambrian/precambrian.html

Simple prokaryotic cells in ocean environment; anaerobic; scum=slime=biofilm. A problem in medicine:

"Slime" May Be Cause of Common Childhood Ear Infection


~2.7 bya: blue-green algae: prokaryotes (cyanobacteria): photosynthesis -> O2 production: O2 accumulation by 2.3 bya; 400 million years of rust....

Conversion of anaerobic to aerobic metabolism; accumulation of O3 in last 800 myrs to provide UV protection.

Eukaryotes: single cell: ~1.7 byrs

Land plants: only ~400 myrs ago.

Homo sapiens: ~100K; oldest cave paintings: 35K yrs.

Life: cells: simple membranous compartments; reduced entropy; self replicating units containing carbohydrates, lipids, nuceic acids, proteins; early life: probably RNA based.

Prokayote cells: no internal membraneous organelles. Must survive in varied environments; biofilms=scum. Prokarya, Archaebacteria; To survive harshest conditions: spores


Multicellularity->specialization; sex vs. somatic cells: mitosis vs. meiosis.

Internal environments controlled: individual cells less able to survive varied environments.

Regulated growth: -> developmental mechanisms.

Diversity through speciation:

Diversity through imprecise replication! HIV

Biological studies at different levels:

Reductionist vs. holistic; extremes: bored vs scared to death

Common to all: hypothesis testing: validation or invalidation

Reproducibility: distinction from non-scientific studies.

Experimental approach: objectivity: Pons/Fleischmann