[tolbiny]

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Let me be more clear: Has any scientist ever succeeded in taking a population of single-celled organisms, exposing them to some agent which causes mutations and created a population of something different than what they started with which retained these differences over at least two generations?

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I'm a buffoon some days- There is an excellent example of this- not in single cell organisms, but in Flax plants. This was thought to be a unique situation untill about a year ago where it was found in a second plant- i don't have links to this stuff, but i do have copies of some of these papers, i don't know if they are published on the web.

Here's the setup with flax- it has been used for centuries, its fibers are used to make linen and falx oil has been important in certain economies at different times. It was domesticated several thousand years ago (perhaps even 10k years ago).

Phenotype- the way an organism appears- ie you have blue eyes- we'll call that phenotype BE
Genotype- the genetic coding that results in a phenotype. you can have several different genotypes that result in the same phenotype- ie a gene with the code ACGTAACTAGT could code for blue eyes as could the code TTACTAGGCTAGC


A population of homogeneous flax plants are taken (that is all of the plants look the same and all of their offspring look the same, and all their offsprings' offspring look the same- so we are sure that there aren't recessive genes at work here). You take some of these original plants and stick them in a controlled environment and subject it to stresses (lack of water, lack of nutrients, temperature ranges outside its optimal habitat)- and then use these plants to reproduce. Their offspring are returned to normal conditions- regular sulight/temps ect- and a percentage of their offspring will exhibit a totally new phenotype. For example if all the original plants were Tall with Broad leaves (phenotype TB)- some of their offspring will now have the phenotype SB (short with broad leaves) or perhaps SN (short with narrow leaves). If you bread those with SN or SB- all of their offspring will be the same as the parent- that is SN will have offspring with phenotype SN, SB the same. They will not return to their parents phenotype no matter how many generations you grow them under optimal conditions.
When their genotypes are tested you find major differences between the parents of the original generation (TB) and thier phenotypically different offspring (SN). The amount of genetic material in the nucleus of a cell can be measured, and in this situation the parent (TB) and offsrping (SN) have different amounts of genetic material in their nucleus.