Growing up, down and sideways, and George Clooney.

Ginkgo seedling 1

Ginkgo seedling 1 (Photo credit: Wikipedia)

Often a plant seed will end up in a place that is not particularly suitable for it. In particular it may end up in a gravel path or similar where there is little real soil. Or it may end up in sand which drains quickly and may, if near the sea, contain high amounts of salt.

In such an environment it may grow stunted or may be deformed. For instance Bonsai trees are kept in a small container and kept relative short of nutrients so that stay small and become gnarled and twisted. They may even have their roots trimmed.

Bonsai IMG 6396

Bonsai IMG 6396 (Photo credit: Wikipedia)

One can imagine a society of concerned individuals fighting against the sustained torture of the trees treated in such a manner, but strangely, I’ve never heard of one. Maybe it is because trees can’t scream?

All members of a species have the same genetic make up, the same genotype. All individuals grow in much the same way, to produce similar adult individuals. This is termed the phenotype.

Genetics diagram: Punnett square describing on...

Genetics diagram: Punnett square describing one of Mendel’s crosses, between parents that are heterozygous for the purple/white color alleles. Category:Punnett squares (Photo credit: Wikipedia)

There may be sexual dimorphism, where the female of the species differs from the male of the species, but in most ways, all members of one sex are pretty similar to one another. I am not too dissimilar from George Clooney. My wife is much like Angelina Jolie.

Of course individuals are not identical. I’m slightly taller than George, for instance. This difference can be genetic, or it may be environmental. My genes may be the cause of the difference, or maybe the environment when we were growing up has slightly affected our growth. Our good looks are almost certainly genetic.

English: George Clooney at the Toronto Interna...

English: George Clooney at the Toronto International Film Festival 2011. (Photo credit: Wikipedia)

Sometimes a plant grows in a particular way in one environment will look completely different in another environment. Also a young specimen of a plant may look different from a mature specimen of the same species. Lanceword (Pseudopanax crassifolius) has a juvenile form so different from the mature form that it was initially thought to be two different species.

The environmental effect on the phenotype or expressed shape can be seen in genetically identical twins. One would expect their phenotypes to be identical at all ages, however, while “identical twins” look very very similar there are detectable differences.

English: Comparison of typical zygote developm...

English: Comparison of typical zygote development in monozygotic identical and dizygotic twins. (Photo credit: Wikipedia)

For instance if one twin had suffered a serious illness at a critical stage of growth, then their adult sizes may be significantly different. If one twin had a rich diet and the other twin a restricted diet that also might affect their sizes and expectations of longevity. Scientists can tell a lot about the processes of growth and development by studying genetically identical twins.

A more subtle variation in the phenotype can be seen when populations are considered rather than individuals. A population of moths that lives on darker surfaces may tend to be darker in colour than the same species that lives on lighter surfaces. Since this effect happens slowly, over many generations, it appears to be a genetic change or shift. However this change to the genotype is at a lower level than the species as the lighter moths and the darker ones can interbreed.

A black-bodied peppered moth (Biston betularia...

A black-bodied peppered moth (Biston betularia f. carbonaria) in the Ahlenmoor, a hill moor in northern Lower Saxony, Germany. (Photo credit: Wikipedia)

Some plants look completely different if grown in different environments. The weed that grows in gravel may look completely different from the weed that grows a metre away in a more favourable environment. It’s as if a switch has been thrown which turns on a totally different way of “building” the plant, as it may well be something like that.

If the genome of the organisation is a “program” to “build” the plant, it is perfectly feasible that a lack of resources at an early stage in the plant’s life might well kick in a different path in the developmental process from the path that it would take if resources were abundant.

if (abundant_resources == true)

then build_good_version

else build_poor_version

This is a simple branching process in a computer program, but the process is almost certainly a lot more complex in real life. However the principle is sound, I believe.

English: Capsella bursa-pastoris, Brassicaceae...

English: Capsella bursa-pastoris, Brassicaceae, Shepherd’s Purse, flowers and fuits; Karlsruhe, Germany. The fresh aerial parts of the blooming plant are used in homeopathy as remedy: Capsella bursa-pastoris (Thaspi.) Deutsch: Capsella bursa-pastoris, Brassicaceae, Gewöhnliches Hirtentäschel, Blüten und Früchte; Karlsruhe, Deutschland. Die frischen, oberirdischen Teile der blühenden Pflanzen werden in der Homöopathie als Arzneimittel verwendet: Capsella bursa-pastoris (Thaspi.) (Photo credit: Wikipedia)

A simple iterative process can be used to generate complex shapes that look a lot like real plants. Minor changes to the process can cause significant changes to the end results. Tall thin shapes can morph into shorter bushier ones with a few changes to fixed numbers (constants) in the iterative process.

The phenotype of a plant of a particular species will be similar in all individuals. If an individual has leaves, stem, flowers of a particular sort then the phenotype of an individual in a different (eg poorer) environment, will most likely have similar parts, though some differences will be obvious.

POOR SOIL, DAMAGED BY ACCUMULATED SALT, IS EXA...

POOR SOIL, DAMAGED BY ACCUMULATED SALT, IS EXAMINED BY MEXICAN FARMER, GILBERTO BUITIERREZ BANAGA, NEAR MEXICALI… – NARA – 549083 (Photo credit: Wikipedia)

Maybe the stem into of being long and flexible, it may be a lot shorter and stiffer. Maybe the leaves will be a lot thicker and fleshier in the poor environment plant and may therefore be able to retain water which will be scarcer in the poor environment. Perhaps the flower will be more robust in the harsher environment.

One would expect such variations of phenotype, the poor and the rich, to be implicit in the genome if the wider environment is patchy, with areas of rich soil mixed up with areas where the soil is poor. Otherwise, the ability of the genome to be expressed in multiple ways would likely be bred out of the population, as nature always goes for the simpler rather than the more complex.

English: Edge of a ditch on a gravelly, lime-r...

English: Edge of a ditch on a gravelly, lime-rich soil at eastern Jutland, near the Kattegat. Dansk: Grøftekant på gruset, kalkrig jordbund i Djursland, nær Kattegatkysten. (Photo credit: Wikipedia)

The flexibility of the genome is something that the organism benefits from its whole life. For example there are some fish which live in groups of one male and several females. If the single male is killed by another fish, an octopus or a human being, one of the females will change sex and become male, taking the place of the missing male fish.

I’ll not speculate on how that happens in detail, but it seems that it must be implicit in the genome. The trigger is the absence of the male fish, but how the “genetic program” detects this, I don’t know, but once is does it transforms the largest female into a male, presumably by triggering changes in the genetic organs. That’s bound to be a complex process.

Male and female Gold Molly. Watch the Gonopodi...

Male and female Gold Molly. Watch the Gonopodium of the left fish. Its the male. Left is the female fish. (Photo credit: Wikipedia)

The central idea in this post is that the genome is much like a computer program and that the environmental influences are like the parameters to such a program. This is probably an over simplification in many ways, but by considering it as a program can explain why the same genome can produce such different individuals.

A computer program can be controlled by inputs while it is running, and similarly the environment can shape an organism while it is growing and after it has reached maturity. The idea of organism as computer controlled machine is not new, but I like to bring it out and have another look at it now and again.

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