Distinction between the genome of Humans and Primate

 

The striking similarity between the genomes of humans and African great apes could justify their categorization as a single genus given the many similarities between the biology, life history, and behavior of humans and great apes. Many other notable discrepancies demand an explanation. It is now possible to inquire as to which genes are responsible for those variations thanks to the whole-genome sequencing of the human genome. The chimpanzee genome might be used for comparison, and the genomes of the other primates could be used for confirmation.

The closest living relatives of humans are chimpanzees. About 6.7 to 5.5 million years ago, the ancestors of humans and chimpanzees split apart. It is still quite interesting to study the genetic features that set humans apart from primates. Human and chimpanzee genomes underwent a variety of modifications following the division of their ancestral lineages, including single nucleotide substitutions, deletions and duplications of DNA segments of various sizes, the insertion of transposable elements, and chromosomal rearrangements. Finding the genetic components that set humans apart from chimpanzees and encode characteristics of human physiological and behavioral identities is still of significant interest [1,3]. Calculating the precise percentage of differences between the genomes of humans and chimpanzees is complicated.

Early studies estimated that the human and primate genomes diverged by about 1% [4]. This estimate didn’t consider the non-coding region of DNA and was based on a comparison of protein-coding sequences. However, until 2005, when almost all the sequencing data of both the human [5] and primate (Pan troglodytes) [6] genomes were available, the notion of 99% similarity of genomes prevailed. It was discovered that while longer deletions and insertions cover about 3% of our genome, single nucleotide changes specific to humans make up only 1.23% of our DNA. Furthermore, differential chromosomal inversions and translocations, which can involve entire chromosomes or several mega-base-long areas, account for a significantly larger percentage.

Chimpanzees have 48 chromosomes, compared to the 46 chromosomes that make up the human karyotype [7]. Both karyotypes are remarkably similar in general. There is a significant distinction between human chromosome 2, which was formed due to the combination of two ancestral acrocentric chromosomes similar to chromosomes 2a and 2b in chimpanzees. Additionally, nine other chromosomes contained large pericentric inversions [7]. The human chromosomes 1 and 18 are thought to include two of the nine, and the chimpanzee chromosomes 4, 5, 9, 12, 15, 16, and 17 are thought to contain the remaining seven [8,9]. The chromosomal structure of pericentric, paracentric, intercalary, and Y-type heterochromatin also differs greatly among species; for example, primates have a large extratelomeric heterochromatin area on chromosome 18 [7]. Moreover, a majority of chimpanzee chromosomes contain segments of subterminal constitutive heterochromatin (C-band) referred to as subterminal constitutive heterochromatin blocks (SCBs). These SCBs are not found in human chromosomes. While they are observed in larger African primates, they are absent in humans. The composition of SCBs mainly consists of repetitions of subterminal satellite sequences (StSat). The presence of these SCBs affects the behavior of chimpanzee chromosomes during meiosis, attributed to persistent subtelomeric connections between both homologous and non-homologous chromosomes. This leads to heightened chromatin variability in subtelomeric regions of chimpanzee chromosomes, driven by processes like homologous and ectopic recombination [11].

The dissimilarities observed between human and great ape genomes include variations in chromosomes, repetitive DNA sequences, transposable elements, retroviruses, genetic polymorphisms, gene inactivation events, sequence differences, gene duplications, single nucleotide variations, gene expression disparities, and mRNA splicing variations. Among these differences, the mutation in cytidine 5′-monophosphate (CMP)-sialic hydroxylase stands out as the only one known to result in a comprehensive biochemical and structural distinction between humans and great apes. However, further investigation is warranted to explore the functional implications of other identified genetic dissimilarities.

It’s widely agreed upon that both gene regulation changes and modifications in protein-coding sequences may have greatly influenced the physical differences between humans and chimpanzees. In this regard, sophisticated bioinformatic methods that integrate different OMICS data analyses are becoming crucial for identifying genetic components that contribute to human evolution. Additionally, having appropriate experimental models to confirm the suspected species-specific genomic changes is of utmost importance.

 By: Rubasha

References:

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