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Interesting talk about genetic similarity: There are only ten earthworms between you and the pig?

“You are really a pig” is often used as a ridicule among friends. In recent years, it has been proved by more and more scientific researches that it may really make sense. Scientists compared pig genomes with human genomes for similarity and found that they have extremely high similarities. In other words, humans and pigs do “share” a lot of genes. The similarities and differences between biological genomes constitute a diverse biological world. The incomprehensible DNA code is like a heavenly book, letting the fate of a species be doomed from birth.

In the animal and plant kingdom, there are many species that are similar to human genomes. Among them are close relatives of primates, such as chimpanzees, as well as species that are completely alien to humans, such as yeast and bananas. Which species’ genomes are more similar to the human genome? What is the reason for this similarity? What is the use of studying genetic similarity between different species?

Those species “similar” to humans

chimpanzee

Chimpanzees are currently the most similar animals to the human genome. Studies have shown that the similarity between the chimpanzee genome and the human genome is 98.6% to 99%. From the perspective of morphological characteristics and reproductive processes, chimpanzees are very close to humans, and it is not surprising that the genomes have high similarities. Evolutionary genomics studies have shown that the ancestors of humans and chimpanzees separated between 5 million and 6 million years ago, and each evolved into their current form.

The genomes of other primates are also very similar to the human genome. For example, the similarity between gorillas and humans is 98%, and that of red gorillas is 97%. In addition, various monkeys and even lemurs have “shared” more than 90% of their genes with people.

Cat

Current research shows that the genomes of cats and humans are as similar as 90%. This also reflects that the wisdom of cats may exceed our inherent impression of them. The domestication of cats by humans occurred about 10,000 years ago, and it may be that cats actively committed themselves to this symbiotic relationship. Evidence shows that wild cats at that time used voles hunting as a bargaining chip to approach humans, so as to obtain a little extra protein and food.

Cows

Yes, you are not mistaken. Our genome is about 80% similar to that of cows. This data is even higher than that of rodents that share a closer common ancestor with us. The explanation given by the scientists is that the smaller size of rodents gives birth to a shorter reproductive cycle and stronger reproductive ability, which greatly accelerates the evolutionary ability of the population and the process of gene mutation.

Mouse

If you only compare protein-coding genes, 85% of the genes in mice are similar to humans, but when comparing the non-coding RNAs of humans and mice, only 50% are similar. Scientists estimate that the ancestors of mice and humans separated about 80 million years ago and evolved separately. As the most commonly used model animal in scientific research, the high similarity to the human genome is a very important reason for the mouse.

Drosophila

Fruit flies, which seem to be very different from the human body and have completely different appearance characteristics, are 60% similar to the human genome. Many people may not believe it, but the results of the genome comparison do prove that more than half of the genes in humans are similar to those of fruit flies.

Chickens

The way chickens reproduce is completely different from that of mammals. Although there are huge differences in breeding offspring, the results of genome comparison show that chickens still have 60% genes similar to humans.

banana

The only plant in the inventory appeared, and it was bananas! A creature that is not even an animal has 50% genetic similarity with humans. Although unbelievable, from a biological point of view, there is indeed a reasonable explanation, which we will introduce in detail later.

yeast

Yeast is a single-celled fungus. Because it is often used in biological experiments, someone compared its genome with that of humans and found that this single-celled organism still has 26% genes similar to humans. Why are there no other common animals in the inventory

Many common animals are absent from the inventory, which does not mean that there are only these 8 species in nature that are similar to the human genome. The reason why these 8 organisms are listed is that humans have already sequenced their genomes, and some scientists have completed the comparison work.

Whole-genome sequencing is time-consuming, labor-intensive, and expensive, so most of the organisms that have completed whole-genome sequencing are scientifically valuable and economically valuable organisms. For example, the Australian koala just completed the whole genome sequencing in 2018. The koala brings direct economic benefits of 1 billion U.S. dollars to Australia every year, and it is loved by the people of the world. It is not too much to think of having its own genetic map.

There must be many species that are very similar to the human genome in nature, but because the whole genome has not been sequenced, there is no way to compare the similarity, and the specific similarity data is not known to humans.

What is the standard for similarity comparison

The genomic similarity mentioned above mostly refers to the similarity of genes encoding proteins. However, in human chromosomes, coding genes only account for 1.5%-2% of the entire DNA sequence, that is to say, the other 98% regions are not used for similarity comparison.

Why can it be said that two species are similar in comparison with so few intervals? This is because most of the genes that function in organisms are these coding genes, and other non-coding regions are considered “junk regions.” Therefore, just by comparing the gene sequences of these proteins, the similarity between different species can be judged.

However, as scientists have deepened their understanding of chromosomes, it has been discovered in recent years that these “junk regions” will also indirectly affect the physiological activities of cells by transcribing non-coding RNA or folding chromosomes. Therefore, the current comparison results are not accurate enough. I believe that as we continue to interpret the laws of life, more scientific results will be obtained.

Why are bananas 50% similar

Why do creatures such as bananas, fruit flies, chickens, and yeast, which are so different from humans, still have greater similarities?

First, we explain this problem from the perspective of the basic composition of the organism. Whether it is yeast, bananas, fruit flies or chickens, they are all eukaryotes, and eukaryotes are made up of eukaryotic cells. All eukaryotic cells have the following characteristics: have a nucleus composed of chromosomes, nucleoli, nucleus fluid, double nuclear membrane, etc.; have endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria and other organelles; have developed Cytoskeleton system: the transcription method is basically the same; etc.

Although the appearance of these different species is very different, the basic structure is similar from the cellular level. Since the formation of these basic structures is determined by genes, it is not difficult to understand why plants and microorganisms still have a certain similarity with the human genome.

Secondly, it can also be explained from the perspective of biological evolution. Whether it is animals, plants or microorganisms, they all evolved from a common ancestor. Therefore, some genetic characteristics of the common ancestor are more or less left between different organisms.

As each species evolves in different directions, the differences between genes are getting bigger and bigger. This is why among the above-mentioned organisms, chimpanzees have the highest similarity with the human genome, while yeast has the lowest similarity with the human genome.

What is the significance of cross-species gene comparison

As more and more species complete genome sequencing, we will discover more plants and animals that are similar to the human genome. In fact, the entertainment effect of comparing very different species exceeds the practical significance. However, it is the most powerful research method of evolutionary genomics to conduct similar genetic comparison studies on species with relatively close genetic relationships from an evolutionary perspective.

Through gene comparison, it is possible to clarify the genetic relationship of different closely related organisms, determine the approximate period of their interspecies differentiation, grasp the context of species evolution, and so on.

Although the existing creatures on the earth have gone through hundreds of millions of years of evolution, they can all be traced back to a common ancestor. From this perspective, it is not worth fussing about having 50% of the common genes with bananas.

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