When it is necessary to learn some physiological characteristics of human health conditions, scientists and researchers address genetic studies and focus on the peculiarities of the human genome. A number of nucleic acid sequences are encoded as deoxyribonucleic acid (DNA) to store the hereditary material. Almost every cell in the human body is coded by the same DNA and located in the cell nucleus (Menon 170). There are four chemical bases where DNA information may be found, namely thymine (T), cytosine (C), adenine (A), and guanine (G) (Minchin and Lodge 434). Every element in the system contains certain associations between genetic variation, explaining the idea of the evolutionary process and the relationships between humans and other representatives of the primates group like chimpanzees. Despite a number of evident similarities between primates, this paper will examine some meaningful differences between human and chimpanzee DNA, including the number of chromosomes in a karyotype, molecular and cellular phenotypes, and mutation speed.
During the last several decades, scientists developed their studies to identify the similarities and differences between humans and chimpanzees. On the one hand, most people believed that the chosen species should have different genetic makeups due to their transposable elements (TEs) and the possibility of moving from one genome location to another (Suntsova and Buzdin 4). On the other hand, researchers revealed that human and chimpanzee genes are nearly identical after their genomes were sequenced and studied. At the beginning of the 2000s, scientists found that the difference between human DNA and chimpanzee DNA in terms of single-nucleotide alterations was 1.23%, while larger deletions and insertions introduced a 3%-difference (Consortium, qtd. in Suntsova and Buzdin 2). Looking at the cladogram of primate species, homo sapience (humans) and pan troglodytes (chimpanzees) share similar characteristics of assembly quality, DNA methylation, gene expression, and proteomics (Kuderna et al. 66). Therefore, when people say that human and chimpanzee DNAs are 99% identical, this statement should be considered true. Humans and chimpanzees are the closest relatives in the animal kingdom, and their physiological and behavioral similarities and differences should be discussed from the DNA composition.
Talking about DNAs in chimpanzees and humans, one should admit the importance of understanding karyotype differences in both species. A karyotype is a complete and constant set of chromosomes, including their number, size, and shape, under natural selection control (Ibragimov 9). Analysis of karyotypes plays an important role in identifying structural changes like insertions, deletions, translocations, duplications, or inversions (Ibragimov 9; Suntsova and Buzdin 2). Even though the karyotypes of the chosen species are similar in most cases, the difference lies in their numbers: 46 chromosomes in humans and 48 chromosomes in chimpanzees and other primates (Suntsova and Buzdin 2). Ibragimov underlines that the origins of such biological consequences remain poorly studied and are usually related to the gene-centric evolution peculiarities (9). Major differences are observed in chromosome 2 (fusion of ancestral chromosomes 2a and 2b in chimpanzees) and pericentric inversions in chromosomes 1, 4, 5, 9, 12, 15-18 (Suntsova and Buzdin 2). Y chromosomes are not equal in size: the human Y chromosome is bigger than the chimpanzee Y chromosome (Cechova et al. 26273). These chromosomes are responsible for making males, which explains a critical number of male genes.
At the same time, there is an ambiguous argument that the changes in chromosome 2 in humans and chimpanzees should not be explained as a fusion outcome. Because humans evolved from apes about 3-5 million years ago, it is hard to understand why chromosome fusion provoked those great differences in such a relatively short period from the evolutionary perspective (Tomkins 222). Some researchers define the fusion site as degenerated because of the perfect telomere arrays (TTAGGG) with no evident corruption (Tomkins 222). Such fusions cannot remain normally healthy, and some mechanical failures in genomic integrity should be noticed. The opponents of the fusion idea used the small size of the site (798 DNA letters) and the inconsistency of telomere sequences. If the length of telomere sequences is about 5,000-15,000, the fused telomere signature should be about 10,000-30,000, but not 798 (Tomkins 222). Another controversy is related to the DDX11L2 gene and its intron-exon boundaries. Fusion sequence cannot be inside a functional gene where various cellular processes occur. Therefore, the formation of new genes due to fusion is questionable and a real threat to the fact that humans evolved from apes.
Scientists pay attention to the DNA regions that are non-coding and called junk DNA. In most cases, DNA sequences encode proteins and share the instructions for the organism to develop and store all the necessary information about hereditary and evolution (Singh and Sophiarani 422). However, the number of DNA in each cell varies, and it is hard to follow each genetic sequence, which results in the production of non-coding ribonucleic acid (RNA) components or the creation of junk or non-functional DNA. In human genomes, as well as in most primate genomes, about 98% are non-coding (Lee et al. 892). Susumu Ohno was the first scientist who noticed that some DNA did not have the necessary adaptive benefit for the organism and offered the term “junk DNA” to cover this observation (Fagundes et al.). This type of DNA controls the expression of genes and may explain differences in human and chimpanzee brains outside the protein-coding genes. Junk DNA’s usefulness is in understanding the human brain evolution through the complexity of genetic mechanisms and neurons’ genes. Its purpose is to ensure that chromosomes are properly formed in the cell’s nucleus for survival.
Talking about the differences between human and chimpanzee DNA, the genealogy of both species should be examined. Mitochondrial DNA (mtDNA) is a chromosome in the cellular organelle, mitochondria, and its sequence defines the haplotype, a unique combination of genomic variants – polymorphisms (Amorim et al.). A human haplogroup is a group of individuals who share common genetic characteristics inherited from a common ancestor. Applying the knowledge about a particular haplogroup, a person can trace ancestry, find a place in a human family tree, and establish a connection. DNA similarities in humans and chimpanzees prove that these species have a single ancestor who might live 3-6 million years ago. The differences in their DNAs prove changes within generations and the possibility of mutation that occurred at a specific time. Maternal and paternal haplogroups exist and are determined by DNA polymorphisms. The short tandem repeats (STRs) are in the Y chromosome to trace male lines, and the single nucleotide polymorphisms (SNPs) are found in the Y chromosome and mtDNA to trace male and female lines (Mahal and Matsoukas). Thus, human haplogroups may tell a picture of the true human genealogy to some extent.
The speed of corruption of mutation in human and chimpanzee DNA is another diversity for consideration. Mutations and DNA changes happen in any population, are the location of these shifts is random. DNA mutation is a DNA sequence change when one genome segment is replaced with its reverse complement (Potapova et al. 1). In human and chimpanzee DNA, specific mutations are in the genes involved in sialic acid metabolism, namely ST6GAL1, ST6GALNAC3, ST6GALNAC4, ST8SIA2, and HF1 (Suntsova and Buzdin 3). Male mutations and corruption are highly reported, while female cell division is not as quick and evident, which promotes the concept of a stronger male mutation bias (Cechova et al. 26276). It means that males pass more mutations to their next generations, and female rates continue to decrease. However, male chimpanzee DNA is characterized by faster mutation rates compared to humans because of faster cell division produced in sperm. One of the possible ways to compare the differences in mutation rates is to observe progeny species and consider the impact of radiation, chemicals, and other environmental factors that might corrupt DNAs.
In general, human and chimpanzee DNAs have their specific similarities and differences, which explains the connection between the species. One of the most evident facts is that the chosen DNAs are almost identical, explaining the use of chimpanzees and other animals from this class for human research. At this moment, scientists accept the statement that about 99% of human DNA is similar to chimpanzees. However, some chromosome differences cannot be ignored, and the discussions about the fusion of chromosome 2 emerge in genetics and biological studies. Each DNA has its purpose, but DNA compatibility in the chosen species is evident.
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