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Biology LibreTexts

3.5: So what do we mean by genetic factors?

Here the answer is empirical. Traditional plant and animal breeders had come to recognize that offspring tended to display the same or similar traits as their parents. This observation led them to assume that there was some factor within the parents that was expressed within the offspring and could, in turn, be passed from the offspring to their own offspring. A classic example is the Hapsburg lip, which was passed through a European ruling family for generations.70

Figure 3.5.1: King Charles II, the last Habsburg king of Spain, displayed the "Hapsburg lip" in reference to heredity of their Austro-Hungarian monarchy via successive inbreeding. King Charles suffered from both physical and mental disabilities; he could not chew his food and had a reduced intelligence. He was also impotent and had no heirs to the throne.

In the case of artificial selection, an important to keep in mind is that the various types of domesticated organisms produced are often dependent for their survival on their human creators (much like European royal families). This relieves them of the constraints they would experience in the wild. Because of this dependence, artificial selection can produce quite exaggerated and, in the absence of human intervention, highly deleterious traits. Just look at domesticated chickens and turkeys, which, while not completely flightless, can fly only short distances and so are extremely vulnerable to predators. Neither modern corn (Zea mays) or chihuahuas, one of the smallest breeds of dog developed by Mesoamerican breeders, would be expected to survive for long in the wild.71

A single cell of the bacterium E. coli would, under ideal circumstances, divide every twenty minutes. That is not particularly disturbing until you think about it, but the fact is that bacteria multiply geometrically: one becomes two, two become four, four become eight, and so on. In this way it can be shown that in a single day, one cell of E. coli could produce a super-colony equal in size and weight to the entire planet  - Michael Crichton (1969) The Andromeda Strain


  1. 'Imperial Stigmata' The Habsburg Lip, A Grotesque 'Mark' Of Royalty Through The Centuries!: http://theesotericcuriosa.blogspot.c...rial-stigmata- habsburg-lip.html
  2. How DNA sequence divides chihuahua and great dane:


  • Michael W. Klymkowsky (University of Colorado Boulder) and Melanie M. Cooper (Michigan State University) with significant contributions by Emina Begovic & some editorial assistance of Rebecca Klymkowsky.