Humans are great apes and belong to the same order as human primates as chimpanzees and gorillas. Although there are many similarities between humans and chimpanzees and gorillas in morphology, habits, physiology and behavior, the number of chromosomes in humans and chimpanzees is different, with humans having only 23 pairs of chromosomes, while human primates such as chimpanzees and gorillas have 24 pairs of chromosomes. This discrepancy has been a long-standing concern for evolutionary biologists, geneticists, anthropologists, and life science researchers, with hypotheses and theories emerging. This article explores these issues for you.
Preliminary chromosomal geometry in humans and chimpanzees
In general, chromosomes are cellular organs in an organism responsible for carrying genetic material, and a chromosome needs to divide into two true chromosomes when germ cells divide, and these two chromosomes are passed on to the maternal and paternal lines of offspring, respectively. The nucleus contains a group of chromosomes that can be classified and numbered according to characteristics such as location, size, morphology, and color, and in fields such as oncology, genetics, and life sciences, chromosomes are often used for biological classification, disease diagnosis, and genetic analysis.
In general, the number of chromosomes in a species is a major genetic trait and an important point of change in the evolution of the species. In primates, changes in the number of chromosomes play a crucial role in the evolution and differentiation of species. According to scientific studies, the variation in the number of chromosomes in primates is quite complex, and it is not reliable to determine the evolutionary history of primates solely by changes in the number of chromosomes. In fact, changes in the number of chromosomes involve the fusion, division and evolution of chromosomes, so they are no less complex than the species itself.
Second, the differentiation of chromosomes in humans and chimpanzees
Chimpanzees and humans evolved to diverge about 6 million years ago, and the number of chromosomes in early primates changed as a result. In the preliminary geometry of human chromosomes, 23 pairs of chromosomes can be divided into two groups, 22 pairs of autosomes and 1 pair of sex chromosomes, of which the X chromosome and Y chromosome are inherited from the maternal and paternal lines respectively, the X chromosome is the sex chromosome carried by most women and the Y chromosome is the sex chromosome unique to males. Unlike humans, chimpanzees have 24 pairs of chromosomes, of which 23 are regular chromosomes and one pair is sex chromosomes.
According to many evolutionary biologists and geneticists, this difference in the number of chromosomes is likely due to the fusion of two chromosomes of the human chromosome. According to these views, a more popular influencing factor is the joint fusion theory.
Third, what is the joint fusion theory?
Junction fusion theory suggests that human chromosomes 2 and 3 were fused from two different chromosomes in early great apes. This event occurred in the course of early humans and human ancestors, and there are many reasons for the convergence. Some favorable factors include accelerators and translocations of repetitive sequences, all of which can lead to chromosomal stringing and eventually fusion.
Building on the junction fusion theory, some researchers believe that the same fusion event occurred in the evolutionary history of other species of great apes, such as changes in the chromosomal hierarchy, number, and distribution of chimpanzees or orangutans. Therefore, the linker fusion theory is a good explanation for the fact of the number of chromosomes in human cells and is not enough to explain the argument.
Of course, there are other hypotheses that are also controversial, such as the joint splitting theory and the rich text deletion theory. Junction splitting refers to the chromosome exchange event that occurred during the evolution of early ape chromosomes, that is, parts of the two pairs of chromosomes were broken and reconnected, forming new chromosomes and changes in the number of chromosomes. The rich text deletion theory believes that the rich text (that is, the repeat sequence) in the human DNA sequence is broken by chromosomes during the duplication process, and the chromosome fragments are rearranged into new chromosomes, resulting in a decrease in the number of human chromosomes.
However, the joint fusion theory is still widely accepted explanation. For the study of human evolutionary history, various technical means, such as chromosome band analysis, DNA sequence comparison, genetic map construction, etc., various new evidence and explanations can continue to strengthen and support this hypothesis. For example, using the knockout of the ERT (a port-supporting enzyme) gene, in vitro culture of human and gorilla cells found that changes in chromosome port length and different rates of shortening evolution likely explain the difference in the number of chromosomes in humans and gorillas.
epilogue
In summary, the number of chromosomes in humans is different from that of most primates such as chimpanzees, and this difference is mainly due to the chromosomal fusion process in early apes. The articulation theory is now widely accepted that human chromosomes 2 and 3 were caused by the fusion of two different chromosomes in early apes and had a profound impact on human genetic variation and evolutionary history. Evolutionary biologists and life science researchers continue to explore this question, looking for more accurate evidence and explanations to further our understanding of human evolutionary history.