Author/Zheng Tao, Han Ce
Everyone often walks the zebra crossing, there should be an impression that the zebra crossing is brushed white paint on the black road, that is, white stripes on a black background. So the question is, is the zebra white on a black background or a black stripe on a white background?
If you pluck open the zebra's hair, you'll see that their skin is black. But zebras are not white on a black background, because the black lines you see are black hairs on black skin, so the zebra is black and white on a black background.
In nature, in addition to zebras, there are many animals with spots and stripes, such as cattle, golden leopards, and even domestic pet cats, dogs, etc., these gorgeous fur patterns are fascinating. So how did these beautiful animal fur patterns come about? Is it possible to artificially design some patterns that resemble animal markings as a substitute for animal fur?
Genes are the brushes of the blob
Different species have unique spot characteristics, even if it is the same species, there are differences in the spot map of different individuals, with their own unique patterns and stripes, spots. This is also a characteristic of biodiversity that has emerged in the long process of biological evolution.
The various patterns of animals are related to the distribution of pigments, which is the result of a long evolution. The spot pattern of animals has the effect of hiding and confusing. For example, China's dairy cows are mainly "black and white flower cows", which are crossed with Holstein cattle and Chinese cattle, and the dairy cow breed is obtained through long-term selection; the stripes of zebras will produce special visual effects when they run, creating visual obstacles for pursuers to escape smoothly. The leopard hiding in the jungle, because of the speckled pattern on the body as camouflage, can be surprisingly successful in the process of hunting.
From the perspective of life sciences, as early as 1953, the American scientist J. Watson and the British scientist F. Crick published a paper formally proposing a model of the double helix structure of DNA, which has since opened the door to the genetic world. The importance of DNA in the transmission of information in life was discovered, and the control of traits by genes became the mystery of life. In 2003, the sequencing work of the Human Genome Project was completed, revealing the secrets of 25,000 genes and 3 billion base pairs in the human body. Genes can be decisive and have become the consensus of the scientific community. With the development of science and technology, in the field of life science research, the research results on the gene regulation mechanism of different organisms and different traits are increasing, and the research on the coat color regulation genes of fur animals is becoming more and more in-depth.
Schematic diagram of a model of the structure of the DNA double helix
The study found that the coat color of animals is mainly determined by the type and distribution of melanin produced by melanocytes. Mammalian melanocytes can produce two different types of melanin, the most important of which is the yellow and reddish brown melanin and the black and brown eumelanin, and the quality and ratio of phycolanin to eumelanin determines the proportion and distribution of the final color of the hair and skin.
There are many major candidate genes for regulating fur color in fur animals, mc1R gene, Agouti gene, TYR gene and other more than 100 genes have an impact on animal coat color, of which MC1R gene and Agouti gene are the key genes that have been studied earlier and have been confirmed to regulate mammalian coat color variation.
Melanin formation and movement of melanocytes
There are differences in the MC1R gene sequence of different organisms, these differences are mostly caused by mutations, which will cause changes in animal coat color, and can be passed on to offspring, MC1R gene as one of the important candidate genes for controlling coat color, which has attracted widespread attention, and researchers in different fields have conducted in-depth research on the structure, function and mechanism of action of MC1R gene. For example, the coat color of Chinese Holstein cows is one of the important characteristics of their breeds, and it is directly related to the production performance of milk and meat. By detecting the bull MC1R genotype, it is possible to screen out individuals with more economic value and ensure the stability of the offspring's flower color.
The coat color of animals is mainly determined by the type and distribution of melanin produced by melanocytes
The coat color of Chinese Holstein cows is one of the important characteristics of its breed, and it is directly related to the production performance of milk and meat
Because genes in the process of determining coat color, will be affected by many factors, such as the environment, genetic mutations, metabolic pathways, etc., will cause differences in the final coat color.
In short, from the perspective of life sciences, different species have different genes, resulting in differences in coat color. There are also genetic differences between different individuals of the same species, resulting in individual differences.
The mathematical and physical mystery of animal markings
If you look closely, you will find that in nature, the body and tail of the zebra are striped, while the leopard is spotted, and the tail is spotted and striped. There seems to be no animal whose body is striped, while the tail is spotted. So how can this phenomenon be explained? Is there a need to follow physical and chemical laws in the process of genetic control of coat color? After all, the metabolic processes in the cells of living organisms are chemical reaction processes.
If we trace the origin of pigments associated with coat color, they are all related to neural crests during embryonic development. The neural crest is a population of multifunctional cells with high migration capacity. During the development of animal embryos, neural crest cells migrate from the nerve plate to the epidermis and dermis, after which they differentiate into precursors of melanocytes and eventually into melanocytes. In this process, melanin formation and the movement of melanocytes can be analyzed from a physical and chemical point of view.
As early as 1952, a year before the discovery of the DNA double helix structure model, the British scientist Turing published a paper proposing to use the reaction diffusion equation system as a basic chemical reaction model for biological forms, describing the reaction of different chemical substances together and diffusion to the surface. This theory explains the physicochemical processes of organisms in the growth process, including cell division and differentiation, and also explains why organisms have different forms during the growth process.
From a mathematical point of view, the system of reactive diffusion equations defined on the surface of a cylinder represents a mathematical model of pigment diffusion, the shape and size of the fur area, and its diffusion wavelength. The system of nonlinear reaction diffusion equations written in this way is generally impossible to find the expression of the solution, but according to Turing's idea we can judge the stability of the constant solution and get the formula for linearizing the solution of the equation near the constant solution. This formula is a Fourier series, there are many factors that affect this function, the most important factor is the ratio of body length to waist circumference, the smaller the ratio, the more likely to appear spotted, the larger the ratio, the more likely to appear striped. Therefore, it can be seen that in nature, slender animals such as snakes appear mostly striped spots. The same organism should use the same system of reaction diffusion equations, so if the tail is streaked, the body is less likely to appear streaked.
There are now many researchers in different fields, through the method of building mathematical models, using computer simulations to predict different space-time maps, and find some common characteristics with the natural patches. But at present, there is no theory that can accurately predict the change of coat color of a certain organism from birth to the end of life.
In order to uncover more mysteries of biological coat color, it is also necessary for biologists, mathematicians, physicists and chemists to work together to analyze and study from multiple angles.
This article is from the "Knowledge is Power" magazine, the original title of "The Genetic Code of Spots and Stripes", the authors Zheng Tao, Han Ce, there are deletions, reprint please indicate the source.