10 fingers and 10 toes

[Ooops! Late again.]

The seed pod of milkweed (Asclepias syriaca)

The seed pod of milkweed (Asclepias syriaca) (Photo credit: Wikipedia)

Most living things come from seeds or eggs. A fertilized egg or seeds has all the information in it to generate the organism that springs from it. All the organs of the organism are implicit in the egg or seed, but minor details, like freckles or fingerprints are not encoded in the egg.

The environment and chance play a part in the final shape of an organism. A seed may fall in a good environment or it may fall in a less favourable environment and the shape of the organism can be totally different in the two environments, to the extent that an unwary botanist may categorise them as two different species.

English: An icon depicting the Sower. In Sts. ...

English: An icon depicting the Sower. In Sts. Konstantine and Helen Orthodox Church, Cluj, Romania. Español: Ícono representando la parábola del sembrador, en la Iglesia Ortodoxa de Helen, en Cluj (Rumania) (Photo credit: Wikipedia)

This property of plants was used by the writer of the Christian gospel in the Parable of the Sower (Matthew 13:3-23). Interestingly this comes just before the part where the Gospel writer expounds on Jesus’ reasons for teaching in parables.

Some plants and animals change significantly as they mature. Lancewood is so different as a mature plant from its juvenile form. The juvenile leaves are narrow and spiky while the mature leaves are broader and softer, and while there are competing theories as to why this is, my favourite theory is that the juvenile plants had to discourage browsing by animals, and in particular the extinct bird called the Moa. Since the Moa is extinct this theory cannot be tested!

English: Giant Haast's eagle attacking New Zea...

English: Giant Haast’s eagle attacking New Zealand moa Français : Aigle géant de Haast attaquant des Moas de Nouvelle-Zélande ; l’extinction des moas suite à leur chasse (surprédation) par l’homme a entrainé la disparition de cette espèces d’aigle. (Photo credit: Wikipedia)

Japanese horticulturists have used this feature of organisms to fit themselves to the environment to create miniature trees in a pot. Basically the tree is grown in a small container which obviously can’t maintain a full sized tree and as a result a perfectly formed miniature tree can be formed with care, sometimes over long periods of time.

It would seem obvious that you can’t produce bonzai human beings, but in fact this can be done. Whenever a drought or famine hits a country the children who grow up there are small and underdeveloped (as well as having other deficiency problems.

Medical X-rays. Broadening of epiphysis with e...

Medical X-rays. Broadening of epiphysis with erlenmayer flask deformity. Commonly seen in rickets. (Photo credit: Wikipedia)

When researching this topic I came across an article on the Internet which discusses this topic, and the authors state in part:

Therefore, by coding for proteins, genes determine two important facets of biological structure and function. However, genes cannot dictate the structure of an organism by themselves. The other crucial component in the formula is the environment.

This overstates the role of the environment a little, I feel, as in most cases the organism’s structure is determined in the most part in its genes, so that it looks much like any other member of the species. It is only when the environment is unfavourable (as in the case of the bonzai trees) that the gene expression leads to significantly differently formed individual. Droughts and poor soils will also leads to significantly differently formed individuals, but those are deficiency effects.

Early succession on poor, sandy soil at Øer, D...

Early succession on poor, sandy soil at Øer, Djursland, Denmark. (Photo credit: Wikipedia)

This is more clearly true in the case of organisms like humans. Unless the environment in which a human grows up is very extreme, there is actually little difference between individuals, and those differences, race, eye colour, hair colour and things like the tendency to myopia are almost certainly genetic.

So I am arguing that genes result in the major characteristics of any organism, except in certain rare cases. Somewhere in the human genome the number of fingers and toes are coded for, and only rare individuals with genetic variations have more or less digits. We don’t all speak the same language, but that is not a genetic trait, though the ability to learn and speak a language may be genetic.

English: Conversion of a DICOM-format X-ray fr...

English: Conversion of a DICOM-format X-ray from a patient of User:Drgnu23, a ten year old male. This is the patient’s left hand, posterior-anterior projection. Identifying tags and such have been stripped. The image is his, released under the GFDL. The image was subsequently altered by user:Grendelkhan, user: Raul654, and user:Solipsist. Français : Radiographie de la main gauche (projection postérieure-antérieure) d’un jeune patient (10 ans) de Drgnu23 présentant une polydactylie. (Photo credit: Wikipedia)

Genes are interesting things. As mentioned in the article, genes can code for structural proteins or for enzymes which affect the chemical reactions in the cell. I suspect that the line between the two is pretty blurred as building the structure of the cell is after all a chemical reaction.

Of course, not only must a cell’s genetic mechanism build and maintain its own organisation, but a cell is part of a tissue, and in, for example, the liver, a cell must maintain itself as a liver cell. Similarly for cells in other organs.

It appears that, as the genetic material is identical across the whole organism, that there must be some way for a cell to “know” that it should develop as liver cell and not as a brain cell. This is done by switching genes on and off, but I don’t understand how this happens in multi-cellular organisms. It seems that there are environmental influences within the organism and within the tissues that determine this.

It’s likely that these environmental influences are based on something like chemical gradients. Otherwise, when a bone is created there would be no way of telling the process of bone creation when to stop. It is evident that it is an approximate influence because fruit flies have different numbers of eye cells between left and right eyes (about 1000). If it were an accurate influence then the number of eye cells would be the same in both eyes.

Apparently scientists do not know exactly how it work either. In this web page, “10 Questions Still Baffling Scientists“, the claim is made that not even the experts know. Of course these Internet lists of things may or may not be accurate, but it is an interesting link.

Of course fractal generation programs can be used to generate pretty good imitations of the structures of trees, and changing a few parameters fed to the fractal generation programs can change the shape of the “tree” from a bushy structure to an extended poplar type structure.


[Fractal] (Photo credit: Wikipedia)

Some similar mechanism might be involved here. Fractal programs are simple, can produce a wide range of shapes. The trouble with fractals is that there is usually no way to stop the shape generation, so any stopping mechanism is probably not part of any possible fractal method for generating. Some other method for stopping the growth of an organ once it is the right size and shape most likely exists.

From the link above it is possible that this mechanism is not yet known, but it does appear that organ growth and shape is encoded in the genes, and is effected by switching genes on and off. Some fractal type mechanism might be involved.

English: Apprentice. Man and boy making shoes.

English: Apprentice. Man and boy making shoes. (Photo credit: Wikipedia)






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