Biology Dept
Kenyon College
Genes, Environment, and Chance
Fall Section Spring Section 1 Spring Section 2
The character of all living organisms result from the interaction of environment and genes.  For example, the risk of colon cancer is increased by dietary factors such as high fat and low fiber.  But a certain genetic allele (version of a gene sequence) in certain individuals confers a high risk of colon cancer, even with a low-risk diet.
Polymorphism Class Environmental exposure Associated disease
CYP1A1 Activation Smoking Lung cancer
NAT2 Detoxification Smoking Bladder, breast cancer
GSTT1 (null) Detoxification Chlorinated solvents Cancer, toxicity
Paraoxonase Detoxification Nerve agents, pesticides Nervous system damage
HLA-H Nutritional factors Iron in diet Hemochromatosis
TGF-alpha Growth factor Maternal smoking Cleft lip & palate
Locus on chrom. 17 in mice Immune/inflammatory response Ozone Lung inflammation
HLA-DP bet1 marker Immune response Beryllium Chronic beryllium disease (lung disorder)
ALAD Biosynthesis Lead Lead poisoning
Jocelyn Kaiser, Science Magazine,  278:569 - 570,  24 Oct 1997
Genes contain the information of a cell that is inherited by future cells.  Each cell needs to copy its chromosome exactly and pass on an identical copy to each daughter cell.   Of course rare "mistakes" occur -- cells actually have evolved to favor rare mistakes.Why?  (See Week 8, Molecular Evolution)

Experiments designed to demonstrate the genetic or environmental component of a trait generally aim to keep all components constant except the one tested.  As a result, someone who studies Down's Syndrome might conclude that the basis of intelligence is genetics; whereas someone studying lead poisoning would conclude that the basis of intelligence is environmental. Actually, all traits -- appearance, development, behavior -- depend on BOTH genes and environment.

Chance also determines the development of an organism. For example individuals with the chromosome abnormality of Down's Syndrome may develop by chance to a wide range of levels -- some develop so badly they die before birth; others have severe heart defects and other physical problems; mental delays vary from severe to minor; some show few physical problems, and can attend college. None of this variation can be predicted from the genes, only from chance effects in development.

Levels of organization in living systems

The content of the Biology core courses can be viewed as a continuum:
      BIOL 113 ------------------------------------------------ BIOL 112

      Molecule - Cell - Organism - Population - Ecosystem - Biosphere

    KAP -- Transfer of information between levels, by gene expression and development, and by genetic change.