Images at Bottom of Page

In studying the morel mushroom, I found extreme variations in populations which would have been genetically homogeneous. The variations were methods of coping with environmental conditions. I then noticed that plants were doing the same thing in a less extreme way.

Phenotypic variation as an adaptation mechanism is an important biological phenomenon which was not previously known to exist. It is observed as variations in a population which would be genetically homogeneous. The test is random distribution of variation in a population rather than Medelian distribution from parents to offspring.

Scientists have long known about phenotypic variation, and the mechanisms are studied in detail at the molecular level. What isn't realized in science is how, where, when and why it occurs as an adaptation mechanism. The evidence indicates that it exists in all species as a method of coping with routine environmental variations which are too rapid to adapt to. Knowing this removes a lot of confusion in biology.

The assumption is that traits are determined by genes from parents, and variations are all due to variations in genes, except for environmental influences and mutations. But in some cases, variations are found where they are not expected. Often, different laboratories will get different results for the same strains and not know why. A person often notices this with food. Apples which are supposed to be all the same will show variations in flavor. Some of this might be environmental results, but a lot of it is probably phenotypic variation.

In nature phenotypic variation is relied upon to cope with rapidly changing environmental conditions, where genotypic variation is too slow. An example is Elm trees which form seeds at different times in the spring. Each year, the latest frost will occur at different times. Some trees produce seeds after the frost, while others have seeds destroyed by frost.

The mechanisms are heavily studied at the molecular level, because they are involved in embryonic development. Each type of tissue is phenotypically different, while the genetic make-up is the same. This is determined by which genes are turned on, and which are turned off. The only difference with phenotypic variation as an adaptation mechanism is that the variations occur between individuals instead of tissues. With embryos, a signal locks the genes on or off, during early stages of cell division. With individuals, the genes are locked on or off during the reproduction process, but exactly where is not known. It probably occurs as the haploid strands of DNA combine to form a diploid zygote. The newly forming diploid strand of DNA is probably coated with RNA and protein which lock certain genes on or off.

Which genes are turned on and which are turned off appears to be totally random in zygote formation. Randomness of distribution is the identifying feature which distinguishes phenotypic variation from Mendelian distribution.

Knowing this mechanism is important in predicting and accounting for variations. For example, to produce uniform quality fruit, grafting my be preferable to use of seeds, because each seed will produce a different phenotype, while each graft will be the same phenotype as the source. If a strain of yeast is developed for beer production, it's important not to allow it to form spores, because the phenotype changes as spores form. Yeasts appear to rely upon phenotypic variation more than usual due to their limited gene exchange. This is why phenotypic variation is extreme with the morel mushroom—it evolved recently from a yeast and is still physiologically a yeast. Morphology evolves much more rapidly than physiology.
 
Morels

Bindweed

Spurge

Echinacea

Liatris

Top