How many chromosomes do Great Apes have? Why do Humans have 23 pairs of chromosomes and Great Apes 24? (With Reasons, Proofs, Comparison, and More)

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How many chromosomes do Great Apes have?

Great Apes are of four types: Gorillas, Bonobos, Orangutans, and Chimpanzees. All great apes have 24 pairs of chromosomes, meaning that they have 48 (2N=48) chromosomes in each and every cell of their body.

Their present chromosomal presence is due to the cause of recombination, natural selection, mutation, susceptibility to disease, and gene flow that have occurred in their ancestors over the timespan of evolution.

Major research studies were conducted on Chimpanzees by a group of researchers that showcased that in Great Apes like Chimps there are millions of single-nucleotide changes, mutations, and chromosomal rearrangement patterns that can only be seen through detailed genetic analysis of DNA fragments.

This also brings light to how humans differ from great apes like Chimpanzees and others. We will learn more about this in detail. So, just keep reading.

How many chromosomes do Lesser Apes have?

Lesser Apes are of two types: Gibbons, and Siamangs. Gibbons have 22 pairs of chromosomes, meaning that they have 44 (2N=44) chromosomes in each and every cell of their body.

And, on the other hand, Siamangs have 25 pairs of chromosomes, meaning that they have 50 (2N=50) chromosomes in their each and every cell.

As seen after detailed genetic analysis conducted on Gibbons that due to their chromosomal patterns and DNA matching, lesser apes like Gibbons genome can be something about 96% similar to human genome.

Their gene analysis also shows that lesser apes like Gibbons are a connecting bridge between Old World Monkeys like Macaques and the great apes like Chimpanzees. And, this has brought light to both genetic and evolutionary studies overall.

There is a unique feature in Gibbons that is called LAVA transposon (a class of genetic elements that can “jump” to different locations within a genome), and this has led to increased mutation rate and so better environment adaptational features in these lesser ape species and sub-species.

So, what the LAVA transposon did in the past, and will be doing anywhere in the near future? Over the course of evolution, LAVA transposon had caused a very rapid rate of chromosomal disorder and rearrangements such as duplications, deletions, or inversions of large DNA fragments, and this will continue in the future too.

This has contributed a lot to their evolutionary developments overall in comparison to their close relatives.

Thus, at present researchers use gibbons as genetic models for their undergoing research focusing on broadening the implications to human diseases related to chromosomal changes like cancer, etc.


Why do Humans have 23 pairs of chromosomes and Great Apes 24?

As proposed by Charles Darwin it is to be noted here that both Humans and Great Apes shared a common ancestor, which was a kind of an ancestral Ape species that used to live somewhere between 8 and 6 million years ago.

But, here it is to be also noted that both humans and great apes like Chimpanzees had evolved differently from that common ancestral Ape, and became two different species. Their DNA, passed from generation to generation, changed too.

Humans have 23 pairs of chromosomes and Great Apes have 24 pairs of chromosomes because of the fact that the two different ancestral chromosomes of our ancestral ape fused at their telomeres potion (i.e. head-to-head fusion) to form a single human chromosome 2.

This head-to-head fusion of two different ape chromosomes to form a single human chromosome 2 is believed to have happened around 0.75 to 4.5 million years ago.

So, here in the case of Great Apes, there was no such fusion. And, as a result of which they evolved by having the same 24 pairs of chromosomes as there were in the ancestral ape.

And, in the case of humans, the fusion of the two different types of ancestral chromosomes of the ancestral ape caused the formation of a single Human Chromosome 2 and thus decreasing one chromosome pair. This led to the presence of only 23 pairs of chromosomes in humans.

This caused a noted genomic difference between humans and chimpanzees (a Great Ape) over the course of evolution.

So, YES, the common ancestor had 24 pairs of chromosomes, and humans carry a fused chromosome that is the Human Chromosome 2, and this chromosome is unique to the human lineage of evolution.

This is also the reason why Humans and Chimpanzees and Bonobos share a surprising 98.8% of their DNA.

Do you know? Chromosome 2 is the second largest of the 46 chromosomes found in human cells consisting of about 243 million base pairs, and making up around 8% of the total DNA present within our cells.


3 Strong Pieces of Evidence: To prove that Humans have 23 pairs of chromosomes and Great Apes have 24 pairs of chromosomes

In order to give a clear-cut possible explanation as of why Humans have 23 pairs of chromosomes and Great Apes have 24 pairs, various researchers have proposed different possible explanations.

These different possible explanations depend on the below mentioned two mainstream explanations for the discrepancy:

  1. Humans carry a fused chromosome 2, and that the common ape ancestor carried 24 pairs of chromosomes.
  2. Great Apes carry an unknown split chromosome, and that the common ape ancestor carried 23 pairs of chromosomes.

However, after peer-reviewed and peer-research were conducted a noteworthy mutation was noticed on one of the Human Chromosomes (most probably the Human Chromosome 2), and this gave pure evidence as to why Humans have 23 pairs of chromosomes and Great Apes have 24 pairs.

Let’s know the three pieces of evidence that were known after peer-reviewed and peer-research:

Evidence 1: It was seen that after chemically dyeing of the Human Chromosome 2 and after comparing it with that of the Great Apes like Chimpanzee’s chromosomes it was seen that the dye pattern of the Human Chromosome 2 closely matches that of the two separate chromosomes found in Great apes. These two separate chromosomes were: Chimpanzee Chromosome 2, and an extra chromosome that does not match any other human chromosome.

Evidence 2: We all know that a centromere is a constricted central region of a chromosome that separates it into a short arm, and that a chromosome normally has one centromere at which a chromosome’s two identical strands are joined. In Human Chromosome 2 it was noticed that a presumably inactive remaining of a second vestigial centromere is already there.

Evidence 3: Human Chromosome 2 has telomere sequences not only at both ends but also in the middle. Usually, any normal chromosome has telomeres at both ends only, but here it is not the case. These are the additional vestigial telomere sequences placed in the q13 band, far from either end of the chromosome.


Did Neanderthals have 23 chromosome pairs or 24?

Neanderthals (also called Neandertal) were a member of a group of early-staged humans that live something about 2.5 million to 11,700 years ago in the regions of Eurasia from the Atlantic regions of Europe eastward to Central Asia parts, and in the north of present-day Belgium, and in the south towards the Mediterranean and southwest Asia.

Neanderthals had 23 chromosome pairs of chromosomes as they were also species of early humans that are now extinct.

The modern-day humans, great apes, and Neanderthals (those early humans) had that common ancestral ape with 24 pairs of chromosomes.

So, yes, just like in the case of modern-day humans, in the Neanderthals too two different ancestral chromosomes of the ancestral ape fused at their telomeres potion (i.e. head-to-head fusion) to form a single human chromosome 2.

Do You Know? Together with Asian people known as Denisovans, Neanderthals are our closest ancient human relatives.

Both Denisovans and Neanderthals had 23 chromosome pairs of chromosomes, and that the traces of their genetic characteristics remain in our genome.

So, we can also say that Neanderthals were also our close ancestors and they also had that fused Human Chromosome 2 that they got during the course of evolution from that ancestral ape.


Let’s Know More: Comparison of Human and Chimpanzee Chromosome

Human Chromosome

Chromosomes are large strands of DNA that got tightly packaged, coiled, and organized into thread-like structures around proteins called histones that support their structure in each and every body cell. Humans have 23 pairs of chromosomes.

Chromosomes in humans can be divided into two types: 22 pairs of autosomes (body chromosome(s)), and 1 pair of allosome (sex chromosome(s)).

Sex chromosomes or Allosomes are different depending on whether you are male (XY chromosome pairs for male), or female (XX chromosome pairs in female), where X and Y are two different sex chromosomes.

Human chromosomes contain anywhere between 20,000 and 25,000 genes. And that every person has two copies of each gene, one inherited from each parent.

Chimpanzee Chromosome

Chimpanzees have 24 pairs of chromosomes. It is also to be noted that Humans and Chimpanzees share a surprising 98.8% of their DNA, with about 35 million single-nucleotide changes, five million insertion/deletion events, gene duplication, and various chromosomal rearrangements.

The major genomic differences between Human and Chimpanzee chromosomes can be well noticed in the chromosome segment inversions on human chromosomes 1, 4, 5, 9, 12, 15, 16, 17, and 18.

Certain genes such as the Forkhead-box P2 transcription factor which is involved in speech development, other genes that are involved in hearing, smelling, thinking, immune system defense, etc. have evolved a lot and are much more advanced and different in the human lineage.

The results of the Chimpanzee genome project reported that the ape ancestral’s chromosomes 2A and 2B that fused head-to-head to produce the human chromosome 2 showed that no genes were lost from the fused ends of 2A and 2B.

In the site of fusion in the Human chromosome 2, there are approximately 150,000 base pairs of sequence that cannot be not found in chimpanzee chromosomes 2A and 2B.

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