Omnis cellula e cellula, with a twist

Identical? It would seem. But look closely and I think you will agree that it is not so.

Virchow, Schwann, Remak, and Redi were right … Omnis cellula e cellula, id est, All cells come from cells. And yet not all leaves on the same plant are identical. I wonder if you wonder why?

If the component cells of an organism arise from a single progenitor, how is it that individuals can be made up of so many different kinds of cells, cells that look and behave so differently? And how, while we’re at it, can it be that identical twins are not exactly the same, at least as far as things other than their genes are concerned?

The answer to the first question is gene expression. Let us suppose that there is a single gene for each trait. Why does a liver cell act like a liver cell or a cardiac cell act like a cardiac cell? What makes cells behave differently, given that each and every one contains the same genetic information? Consider that the genes that make liver cells behave like liver cells are turned on in liver cells, and the genes that make cardiac cells look and behave like cardiac cells are turned off in liver cells. The obverse is also true. These genes are regulated because the chemical milieu of a liver is such that cells which occur there act like liver cells. There’s something about the chemical milieu of the heart that cells which occur there act like cardiac cells. It is the environment within which a cell finds itself that determines just how that particular cell will function. So that is why, if they all source to a single progenitor, the many trillions of cells which make up the human body develop into a myriad of types.

But what about the other question? How it is that the fingerprints of identicle twins can differ, given that they possess the same genetic material? The answer is in the fine details of embryonic development. Consider that developing embryos cannot occupy the same position at the same time. Because this is so, each experiences a slightly different developmental environment. The ridges and troughs which form the fingerprints develop in the dermal layer of the skin. The dermis is sandwiched between two other layers (the epidermis and the subcutaneous layer) and buckles and folds as the skin moves during development. The pattern of the developing fingerprint is unique because each time it enfolds, even in genetically identical individuals, it does so chaotically. Development is a highly plastic phenomenon.

So, what does this all have to do with the image of the leaves of a Striped Maple seedling? Contrary to what our eyes may tell us, no two of the leaves on this delicate individual can be the same. Their component cells surely have the same genes but these are being expressed in a slightly different way each and every time a leaf develops to unfurl.

leaf

Retrospective thirty-nine (May 2015)

Given the way in which blogs are presented, I am convinced that posts which reside more than a scroll or two behind the most recent are doomed to languish and be forgotten. Because I believe there is value in looking at contributions from days, weeks, and even months ago, I present a post from the month of May, 2015. We were pretty busy through November of last year and the video presented here was the only post to appear during those seven months. This is the thirty-ninth in my series of retrospectives. If you missed any of the others, you can find them all by clicking Retrospective in the tag cloud in the sidebar. Retrospective forty will be posted in December.

Evo-devo-diva

.
In coiled repose, then
embryos unfurl in turn.
Sporophytic thrill.

Fern2

An odd response


Fungi, Plants, Animals
, Protists, and Bacteria. Different, and the same. Each grows to beget more of its kind.

I wonder, why?

Discount the facility of our own view as prurient. Discount our carnal sense and opinions steeped in anthropocentric bias. Love, passion, desire, lust. I cannot agree. To see how senseless, argue the same for any you choose, save you and me.

Perhaps we should recognize that butterflies replicate because they can. Better yet, think ribozymes when contemplating the ancient act of self-replication.

How wrong, you say, to think the answer may be found somewhere between the worlds of chemistry and physics.

I think it entirely correct to imagine that it may be found in an extension of first principles.

The recognition makes the beauty of nature even more unexpected.

Leaf2

The scale of things

l
The aspect was obstructed by neither winter blanket nor summer veil. Air echoed among those that watched.

She stepped lightly, sensitive to the living things beneath her feet.

There, she said. They are very small. Very pretty. She turned to greet them.

We are at ease in a world of tall, wide, deep, and heavy. I worked to reconsider my surroundings, to allow me to see as she did and at this uncomfortable scale. It was only when I stopped and concentrated that I managed. It was only when I focused, that the things she saw so easily, crystallized from out of that place I could not see. At a scale that mattered to them, these were beautiful things indeed. Growing. Developing, in swirled asymmetries.

The individuals you see here are sporophytic. As they grow, these Fiddleheads will unfurl to form the plants we know as Ferns. Sporophytes produce spores which disperse and germinate to produce gametophytes. Fern gametophytes are small and don’t look much like their sporophytic progenitors. Gametophytes produce egg and sperm which fuse to form the sporophyte once again.

Fiddle

Thankful reunions

They began to appear.

Brightly-dressed Finches were first. And then the haunting call of the Thrush. Frogs, Turtles, Fry, Newts, and Peepers followed in turn.

She waited for other friends, many of which she had not communed with since childhood. She hoped that some were already here and if they were, which would she see again after so long a separation?

And they came. Dog Tooth Violet, Spring Beauty, and Wake Robin. Her smile filled with gladness. Although satisfied, she hoped that others, perhaps Hepatica, Squirrel Corn, and Lady’s Slipper, would arrive even if fashionably late.

She has welcomed these reunions of spring, especially.

Fiddle3

Retrospective thirty-eight (April 2015)

Given the way in which blogs are presented, I am convinced that posts which reside more than a scroll or two behind the most recent are doomed to languish and be forgotten. Because I believe there is value in looking at contributions from days, weeks, and even months ago, I present a gallery of images from April of 2015. Hovering an image will reveal its title. Clicking one will take you to a carousel view and you can either move through the collection or click the links to read each post in its original form. This is the thirty-eighth in my series of retrospectives. If you missed any of the others, you can find them all by clicking Retrospective in the tag cloud in the sidebar. As a postscript, allow me observe that seeing these images this morning was poignant, for they document the very last spring lambing at the farm. We surely had a long, and successful, run.

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