Why is it not possible for different species to exchange genes under natural conditions?

The definition of species requires that it cannot be mated to produce fertile offspring, so there will naturally be no gene exchange.

Because there is reproductive isolation between different species.

Reproductive isolation: Individuals of different populations are unable to mate or are sterile or unable to produce reproductive offspring, resulting in no gene exchange between populations.

Because natural selection is based on overbreeding, accumulating enough selection capital, genetic variation has multiple directions, providing survival possibilities for selective evolution.

Overbreeding will inevitably cause some harm, first of all, due to ** reproduction, the environment will be seriously damaged in a short period of time, and even cause extinction to other populations. For example, water hyacinth, officially known as phoenix eye blue, is also called water floating lotus.

In the process of reproduction, organisms will continue to produce variations, many of which can be inherited, are favorable variations to adapt to the environment, and these constant variations are the basis of biological evolution and then overproduction provides the impetus for natural selection, and the survival struggle is used as a means to achieve the survival of the fittest (favorable variation).

Is the answer copy wrong, I think D should be chosen. For example, we often talk about horses and donkeys, which are different species. But it can breed mules.

A population is all individuals of the same species that occupy a certain space for a certain period of time. Individuals in a population are not mechanically grouped together, but can mate with each other and pass on their genes to their offspring through reproduction. Population is the basic unit of evolution, and all organisms in the same population share a gene pool.

The study of populations mainly focuses on their quantitative changes and intraspecific relationships, and the content of interspecific relationships has belonged to the study of biological communities.

Only when two organisms are selected to mate to produce fertile offspring can the two organisms belong to the same species.

For example, mating a horse and a donkey can produce offspring - mules, but mules are not fertile, so horses and donkeys do not belong to the same species.

The ABC options are all correct.

The fact that two organisms have successfully mated and produced offspring does not mean that the two organisms belong to the same species.

For example, horses and donkeys are crossed to give birth to mules, but horses and donkeys are two species with reproductive isolation, and although the mating is successful, the offspring mules are inferential.

There is a complex interrelationship between genes and genes, genes and gene products, and genes and the environment, and this interrelationship forms an intricate regulatory network that precisely regulates the traits of organisms.

1. There are two possibilities for the inability to carry out gene exchange, one is that the same species should be able to carry out gene exchange, but there is geographical isolation, resulting in reproductive isolation, and gene exchange cannot be carried out; The other is not the same species, which is inherently reproductively isolated and unable to communicate genes.

2. There must be reproductive isolation between organisms that cannot communicate genes, and organisms that cannot communicate genes may or may not be the same species;

Imagine if living things didn't exist for reproductive isolation.

Gene exchange is the recombination of genes, the same species, different species can be (offspring are generally sterile, because the offspring have been isolated from the species of both parents (reproductive isolation)).

Gene exchange between species is judged based on whether the genes of one species can be expressed normally in another species (i.e., transcribed and translated into the corresponding proteins). cDNA libraries are built based on reverse transcription of mRNA sequences, in which the preserved genes continuously encode the corresponding amino acids in any species, resulting in the synthesis of normal proteins.

The vast majority of organisms share a set of genetic code). Therefore, gene exchange between different species can be carried out through cDNA libraries. But genomic libraries are built by extracting DNA directly from an organism.

Whereas, the genetic structure of prokaryotes is different from eukaryotes. The genes of prokaryotes are continuous, and all of them can code for proteins. But the genes of eukaryotes are discontinuous and are divided into exons and introns.

Only introns can code for proteins, while introns are staggered with exons. So in the genes of eukaryotes, the region that codes for the protein is not continuous. Therefore, the genes of prokaryotes can be expressed normally between prokaryotes and eukaryotes, so that gene exchange between species can take place.

However, genes of eukaryotes can only be expressed normally in eukaryotes through eukaryotic mechanisms that are unique to eukaryotes, but not in prokaryotes. Therefore, genomic libraries can only carry out some gene exchanges between species. That is, prokaryotic-prokaryotic, eukaryotic-eukaryotic, prokaryotic-eukaryotes can communicate with each other, but eukaryotic-prokaryotes cannot communicate with each other.

It would be nice to figure out the two concepts. The genome is a complete set of genetic information of a species, which generally refers to the total RNA in the nucleus of a species that is transcribed from a certain period of time, which is only the sum of the genetic information in a specific time and space of the species. Therefore, genomic libraries and cDNA libraries are all and part relationships.

Note: Gene expression is spatiotemporal. For example, a frog may express different genes during the tadpole stage than it does during the adult stage.

There is no change in the genome, but the functional genes expressed are different, i.e., the total RNA extracted is different. In other words, there is no difference in the genome library constructed, but the cDNA library is different at different times.

The different construction methods and purposes of the two types of libraries determine the difficulty of isolating and extracting genes.

Some genes in genomic libraries (especially non-digested fractions that cannot be expressed to form mRNA) are difficult to isolate from genomic libraries by some method, affecting their potential for interspecies communication.

There are no introns, promoters, and terminators in the genes of cDNA. In genetic engineering, if a prokaryotic organism is used as a recipient cell, the target gene is a gene from the eukaryotic genome library, and the gene of the eukaryotic genome library contains introns, and there is no intron shearing enzyme in the prokaryotic organism, it will not work, and if the target gene is from the gene of the eukaryotic cDNA library, its gene does not have introns, it can be used.

I don't think that natural selection acts on genes" or "natural selection acts on individuals" or "natural selection of branches for populations" and so on are not true, at least they have no exact meaning. Because the so-called "acting on" is "acting on......influence", and the many levels from the various organic molecules to the entire biosphere are closely related to each other, and an impact on any one of them will inevitably affect the other levels in a chain reaction, so the object of natural selection should be the various levels related to the organism. Only statements such as "natural selection acts directly on individuals" or "natural selection acts on genes in nature" are remarkable.

My opinion on what Butt Ga 415 said is as follows:

An individual is not genetically altered by natural selection" – could a population be genetically altered by natural selection? Does the gene belong to an individual or a population?!Isn't it more reasonable to say that "a gene will be genetically altered by natural selection" than that "an individual will not be genetically altered by natural selection"?

As I have already said, "acting on" means "acting on......genes, individuals, and populations are closely related to each other, and influencing one of them will inevitably affect the other two at the same time, so the statement that "natural selection acts on genes or individuals or populations" has no exact meaning. Isn't that a simple and straightforward logic? This logic is the crux of the matter, and if we don't directly refute this logic, all other arguments are just untargeted.

Taking a step back, even if "acting" is more narrowly defined to "......".direct impact", then natural selection should also act on individuals, not populations. Because natural selection, at least in Darwin's original meaning, is "survival of the fittest", the subject of natural selection is obviously the individual, and most of the time the population does not matter whether it lives or dies, it usually only gradually evolves into one or several new populations (of course, some populations also die out); Only individuals have a clear winner or elimination. In short, individuals live and die, and populations evolve.