lpetrich
Contributor
How the Cat Gets Its Stripes: It’s Genetics, Not a Folk Tale - The New York Times
Although we have succeeded in solving some big biological mysteries, like metabolism and genetics, there is a big one that continues to elude our grasp: genes to shapes and patterns.
That has been the subject of a lot origin-story folklore, usually involving Lamarckian inheritance from something that some ancestor experienced.
But while genetics and metabolism have become very well-understood, development is still largely a mystery. We don't have much of a clue of how to get from genes to shapes, especially macroscopic shapes. The same is true of patterning, especially macroscopic patterning. It is generally agreed that development involve various morphogens in various ways, though they have been difficult to track down.
In 1952, Alan Turing proposed that patterns can be produced by a combination of diffusion of morphogens and chemical reactions between morphogens. The Chemical Basis of Morphogenesis - Turing pattern - Reaction–diffusion system - French flag model - 13.6: Reaction-Diffusion Systems - Mathematics LibreTexts
Some morphogens have indeed been discovered, like those in the Hox mechanism ( Hox gene) Hox genes are expressed in zones along the length of the animal, and the resulting proteins help specify identity along the nose-tail axis. There is a similar system that specifies identity along the dorsoventral axis ( Inversion (evolutionary biology)) and in plants, there is the ABC model of flower development
Turning to patterns, this discovery was made back in 1977:
(PDF) A unity underlying the different zebra patterns
Although we have succeeded in solving some big biological mysteries, like metabolism and genetics, there is a big one that continues to elude our grasp: genes to shapes and patterns.
That has been the subject of a lot origin-story folklore, usually involving Lamarckian inheritance from something that some ancestor experienced.
But while genetics and metabolism have become very well-understood, development is still largely a mystery. We don't have much of a clue of how to get from genes to shapes, especially macroscopic shapes. The same is true of patterning, especially macroscopic patterning. It is generally agreed that development involve various morphogens in various ways, though they have been difficult to track down.
In 1952, Alan Turing proposed that patterns can be produced by a combination of diffusion of morphogens and chemical reactions between morphogens. The Chemical Basis of Morphogenesis - Turing pattern - Reaction–diffusion system - French flag model - 13.6: Reaction-Diffusion Systems - Mathematics LibreTexts
Some morphogens have indeed been discovered, like those in the Hox mechanism ( Hox gene) Hox genes are expressed in zones along the length of the animal, and the resulting proteins help specify identity along the nose-tail axis. There is a similar system that specifies identity along the dorsoventral axis ( Inversion (evolutionary biology)) and in plants, there is the ABC model of flower development
Turning to patterns, this discovery was made back in 1977:
(PDF) A unity underlying the different zebra patterns
Just recently, a followup has been published on domestic cats.To elucidate the relationship between the complex striping patterns of the different species of zebras, a simple conceptual experiment has been performed. Using data from horse embryos, the normal growth of the zebra from early foetus to adult has been reversed to see what happens both to the spacing and to the orientation of the stripes. It turns out that for each species, there is a point in time when all the body stripes would have been perpendicular to the dorsal line and equally spaced. Moreover the spacing is roughly the same (0·4 mm) for the three main species of zebra at this time. This point is during the third week of development for E. burchelli, fourth week for E. zebra and fifth week for E. grevyi. As striping only appears at about the eighth month of foetal development, it seems that the pattern is determined a long time before the cells actually lay down pigment. Further analysis of the pattern so laid down on a rapidly-growing foetus shows how shadow and gridiron stripes can arise. The reason why leg stripes are orthogonal to body stripes cannot however be derived from this phenomenological approach. These results suggest that a single mechanism generating equi-spaced stripes of separation 0·4 mm could lay down the body stripes of zebras and that species differences arise from pattern formation occurring at different times in embryogenesis.