Genetic Difference Between Humans and Chimps

The main genetic difference between humans and chimps is that humans have 23 pairs of chromosomes whereas chimps have 24 pairs of chromosomes in their genomes. Two ancestral chromosome pairs fuse at their telomeres to form human chromosome 2 during evolution. 

Humans and chimps are two species that are very closely related to each other. Humans and chimps have 1.2% of non-coding DNA difference in their genomes that are responsible for all the unmatching characteristics of humans and chimps.  

Key Areas Covered 

1. What is the Human Genome
     – Definition, Genetic Facts
2. What is the Chimpanzee Genome
     – Definition, Genetic Facts
3. What are the Genetic Similarities Between Humans and Chimps
     – Outline of Common Features
4. What is the Genetic Difference Between Humans and Chimps
     – Comparison of Key Differences

Key Terms: Chimpanzee Genome, Human Genome, Number of Chromosomes, Size 

What is Human Genome 

The human genome is the collection of human DNA. Human genetics focuses on the nucleotide sequence of the human DNA revealed by the Human Genome Project (HGP) completed on 14th April 2003. Humans are the most developed members of the mammal order primate. Humans, gorillas, chimpanzees, bonobos, and orangutans are close relatives collectively called the great apes. Homo sapiens is the scientific name of humans. The human genome contains over 3 billion base pairs organized into 46 chromosomes: 22 autosomal and two sex chromosomes. <2% of the human genome contains coding DNA transcribed into mRNA. About 20,000 protein-coding genes are present in the human genome. 98% of it is noncoding DNA, which includes genes coded for tRNA and rRNA, pseudogenes, introns, UTR (untranslated regions of mRNA), regulatory DNA, repetitive DNA, and mobile elements. Though chimpanzees are one of the closest relatives of humans, chimpanzee genome contains 24 paired chromosomes. The human chromosome 2 is the result of the fusion of the ends of ancestral chromosome 2A and 2B. Additional 150,000 bp sequence presents at the site of fusion. Shown in figure 1 is the human chromosome 2 and the additional sequence. The additionally linked genes may copy from the p end of the chromosome 9. 

Figure 1: Human Chromosome 2

There are six chromosomal regions in the human genome that had undergone a strong and coordinated selection over the past 250,000 years. Interestingly, at least one allele maker unique to the human lineage is present in each of the above-mentioned regions. FOXP2 gene and CFTR gene are such markers.  

What is Chimpanzee Genome 

Chimpanzee genome is the whole DNA sequence of the chimpanzee. Chimps genetics also focuses on the nucleotide sequence of the chimpanzee genome with respect to the human genome. The chimpanzee genome project started in December 2003, just after the completion of the HGP. 98% of the sequence of the human and chimpanzee genome is similar. Also, the chromosomes of human and chimpanzee are similar. 

Figure 2: Human and Chimp Chromosomes

Apart from that, highlighted below are some other genetic differences between human and chimp genome. 

1. Chromosome segment inversions on human chromosomes 1, 4, 5, 9, 12, 15, 16, 17, and 18 differ from chimps. 
2. Similar DNA sequences are five times incorrectly assembled in the chimpanzee genome. 
3. The genes involved in the speech development such as FOXP2 transcription factor and the genes for the hearing of chimps differ from humans. 
4. Human and chimp homologous proteins differ in an average of 2 amino acids. 
5. Gene duplications or deletions are the major events that bring the difference between human and chimp genomes.  
6. About 600 genes have undergone a strong selection in the human lineage. Many of these genes have an immunological function. 
7. About 50% change is there in a set of 348 transcription factor genes between humans and chimps.  

Furthermore, the gaps of the genomes near the key genes differ from each other in human and chimp genomes. These gaps differentially alter the expression of nearby genes. The insertion or deletion of junk DNA sequences called the retrotransposons create these gaps.  

Genetic Similarities Between Humans and Chimps 

• The size of the human and chimp genome is similar. 
• Genome sequences of humans and chimps are 98.8% similar. 
• Human and chimpanzee chromosomes are very similar. 
• The mean divergence of chromosomes is similar. 
• Further, the mean divergence of nonpolymorphic sites and CpG sites are also similar. 
• The number of nucleotide substitutions is 35 million.  
• Also, the number of insertions and deletions are 5 million. The total amount of insertions and deletions is 90 Mb.  
• Nucleotide divergence of the mitochondrial genomes is similar. 
• Can find 66% gene duplications in both genomes. 
• 29% of the human and chimp orthologous proteins are similar. 

Genetic Difference Between Humans and Chimps 

Definition 

Human Genome: Human genome is the collection of human DNA

Chimp Genome: Chimpanzee genome is the whole DNA sequence of the chimpanzee

Number of Homologous Chromosome Pairs 

Human Genome: 23 

Chimp Genome: 24  

Unique Duplications 

Human Genome: 88 Genes 

Chimp Genome: 94 Genes 

Conclusion 

The human genome contains 46 chromosomes while chimp genome contains 48 chromosomes. The ancestral 2A and 2B chromosomes fuse together to form human chromosome 2. Hence, the main genetic difference between humans and chimps is the number of chromosomes. 

Reference:

1. “Chimpanzee Genome vs. Human Genome.” MetaPrimate.com, Available Here
2. “Chimpanzee Genome Project.” Wikipedia, Wikimedia Foundation, 25 May 2018, Available Here

Image Courtesy:

1. “Chromosome2Insert” By JWSchmidt at the English language Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “Humanchimpchromosomes” By JWSchmidt at the English language Wikipedia (CC BY-SA 3.0) via Commons Wikimedia