How did the fishspecies form? Below, petsnet will give you a brief introduction:

1. Changes in living conditions are not the reason for the formation of the breeds The living conditions are formed by the breeds of goldfish The reason is that this view is easily accepted by people. It is true that changes in living conditions, the environment in which the organism can undergo some variation, can alter the expression of the organism. This is a well-known fact. But these variations are generally uninherited and most convincing than in fish The experiment of sexual transformation is like the sexual transformation experiment of goldfish, tilapia and crucian carp. When these fish hatch, the juveniles whose gonads have not yet been differentiated are fed with different sex hormones, such as methamphetamine mixed in the feed. Or testosterone propionate and other male hormones, the juveniles develop into males; if fed with feed mixed with female hormones, such as estradiol benzoate or estrone, the juveniles develop into females and are fertile. Note that these sex-transformed fish have changed their expression type due to the influence of hormones in the feed, but their genotype has not changed. Experiments have shown that the sex of goldfish is XY type. Some juveniles fed estrogen, with Normal male fish mate, some of them produce offspring with a sex ratio of 1:3, that is, nearly 25% of females and nearly 75% of males. Male fish mate to obtain a 1:3 ratio. Because only after *Y males are transformed into females through estrogen feeding and fertilized with the sperm of normal male fish, it is possible to develop into a 1:3 ratio, and 25% of the fish will be females. 75% of them are males.

This experimental result proves that sex hormone feeding (i.e. living conditions) only changes in physiological function and expression, but in There is no genetic change, but the original genotype is what works. Changes in living conditions (environment) cannot change its genotype, only its phenotype. Because information cannot be transmitted between organisms and the environment, the environment cannot Determining hereditary traits.

Under the same environmental conditions, goldfish showed different traits in the process of being raised from released semi-housed to house-raised, and from other to pot-raised. The variation of these characters has no direct adaptation relationship with the environment (living conditions). From the external appearance, goldfish is completely different from wild crucian carp, and there is hardly a single character without variation. However, the reasons for these variations are difficult to derive from living conditions. The answer is found in. Because these variations are not beneficial to the goldfish itself. Such as blisters, there is a big round bubble next to the eye, and the eyes are squeezed upward, what is the adaptation? Whether it is raised in ground or in pots, it is not It is necessary; another example is the pearl fish, whose scales are bulging out and look like pearls, which are called pearl scales; another example is gills, pom-poms, etc. What are the adaptability of these mutant characters? It is regarded as a treasure, and it has been preserved through the selection of the inferior and the best, and it has become a rare breed. The variation of other characters is also the same. Some variations such as single tail, complete dorsal fin, residual double tail, etc. have been eliminated, so the general audience sees it. However, these variations of single tail, residual dorsal fin and residual double tail often appear in the offspring of goldfish. These facts are difficult to explain by changes in living conditions, let alone the red-yellow golden crucian carp that was originally discovered is the same as wild crucian carp The same is in a natural environment. Therefore, the change of living conditions as a goldfish product The reasons for the formation of species cannot be established

Second, the factors for the formation of varieties Modern biology has proved that the heritable variation mutation in organisms objectively exists the original data of biological evolution . The occurrence of mutation is not directional. Of course, it should also include the variation adapted to the environment, but the vast majority of it is the variation that is not adapted. The so-called variation suitable for the environment is the result of selection (natural selection or artificial selection), the survival of the fittest, and the elimination of the unfit. With mutation, after careful observation by breeders, different breeds are formed from unconscious selection to conscious selection. With mutants, people can also use them for hybridization and artificial selection to breed new varieties. Hybridization has been widely used in animal and plant breeding, and of course goldfish breeding is no exception. Crossbreeding makes genes recombined, and after several generations of selfing, recessive mutation traits can be stably expressed, and new breeds are gradually formed in the hands of breeders through the selection of the best. Generally speaking, most of the spontaneous mutations occurring in nature are recessive mutations. For example, domestic goldfish species are crossed with wild crucian carp, and the vast majority of their offspring are expressed as wild-type traits. Because it is a recessive mutation, it does not appear in contemporary times, but after several generations of crossbreeding and progeny selfing, the recessive traits in homozygotes can be truly inherited as soon as they appear, and new varieties can be formed.

There are also records about the hybridization of goldfish in ancient Chinese books. For example, Chen Shan (1579 Wanli Hangzhou House Records) wrote: Seven-day potted fish: gold, jade, stage, crystal, and blue. Its exotic products are plum blossom dots, crane top red, and heaven and earth. There are so many names and colors, and I can't fully understand them. The speaker said that the fish is born from the foam. That is, the red and white two-color male and female are affected by each other, and the piebald fish is born. Volume 32, page 12, this shows that piebald is a natural cross between red fish and red fish. This is also true. However, ancient people did not consciously use crossbreeding as a means of breeding. It was not until 1925 that goldfish entered the market. The era of cross-breeding. Through cross-breeding and recombination, new variation characters appear, and many new varieties are cultivated, which is much faster than relying solely on mutation to cultivate new varieties.

The heredity and variation of organisms is that organisms with unity of opposites have the conservative side of heredity to maintain the relative stability of the species; but there is another side of variation, which makes the species appear new variations and get new development. Heredity is relatively radical Variation is absolutely forward. Without heredity, it is impossible to maintain the relative stability of species; without variation, there will be no new characters, and there will be no evolution of species and selection of new varieties, and it is impossible to appear. There are countless species today.

How does mutation occur? This is mainly genetic mutation, but also genetic recombination and other types The mutation of polyploidy, such as polyploidy. The existence of polyploidy is also found in goldfish. The recombination of genes is obtained by crossing to make different genes freely combine in gamete formation. This is one of the basic laws of heredity, called free combination. The law. The recombination of genes provides the diversity of variation and plays a great role in biological evolution. In the work of cultivating new varieties, using the principle of gene recombination can be said to be the most classic and effective method. There are many combinations of traits in goldfish Together, it is a new breed formed by concentrating some genes into one genotype. For example, Chaotian Bubble Eye is a hybrid of Chaotian Eye and Blister Eye, and Dragon Ball (Dragon Eye Pearl) is a hybrid of dragon eye and pearl fish.

Although genetic recombination can invent various new genotypes, it is impossible to produce new genes, just like bricks can be built Buildings of different forms, but red bricks cannot be built into white buildings. Only mutations can generate new genes. For example, the eyes of goldfish, if there is no mutation, then no matter how to carry out hybridization and recombination, it can only be normal. Eyes, but no other eye traits appear. Mutations have occurred, and the traits of longan, overturned eyes and blisters have appeared. Through hybridization and recombination, new varieties of overturned blisters and pearl blisters (pearl blisters) have appeared. It can be seen that , mutation is the basis of biological evolution. Without mutation, organism will not evolve.

The appearance of mutation generally has no obvious relationship with the living conditions of organisms, and living conditions cannot Become the cause of the formation of goldfish varieties. Mutation is not the direction because gene A can both It becomes an allele, and it can also become an allele a2a3, etc. For example, the eyes of goldfish can mutate into longan, upturned eyes and blisters.

In summary, it can be concluded that the reason for the formation of goldfish varieties is due to the three major factors of mutation, hybridization and artificial selection. Among the factors, mutation is the basis, and hybridization and artificial selection are the means. Artificial selection plays an important role in the formation of goldfish species.