Genomes From 240 Mammalian Species Help Explain 100 Years Of Evolution And Human Disease

Certain parts of mammalian genomes have remained the same across species and over millions of years. This suggests that these regions are important.

This is a picture of Balto, one of the most famous dogs in the world. In 1925, during an outbreak of diphtheria in Nome, Alaska, Balto helped deliver serum to children. A new study has found that Balto, and other sled dogs of that time, were genetically healthier than modern dogs.

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There are more than 6,000 mammalian species on Earth, each of them different. Over the past 100 million years, mammals have evolved to adapt to their surrounding environment, resulting in diverse features. However, certain parts of the genome have remained the same across species and over millions of years, a large international collaboration of 30 research teams has found. This suggests that these regions are important, and the researchers believe these could hold the key to understanding human disease better.

The findings were recently published in 11 papers in the journal Science. The collaboration, called Zoonomia Project, investigated the genomic basis of shared and specialised traits in mammals.

Why the authors compare the genomes, instead of studying them individually

The reason why the authors compared 240 mammalian genomes is to observe which parts remained unchanged across species during the course of evolution. Since evolution is a natural phenomenon that helps species adapt over time in response to the changing environment, any part of the genome that remains unchanged must be important. 

A genome is the complete set of genetic information in an organism, and provides all of the information the organism requires to function. It consists of two broad parts. One is the genes, which are responsible for manufacture of protein molecules by the organism.

The other part consists of regulatory elements. These regions do not code for proteins, but instruct other genes where, when and how many proteins they must produce. 

The scientists hypothesised that mutations in these regions of the genome may give rise to new diseases, or may be responsible for some unique mammalian features.

Balto, one of the world’s most famous dogs

One of the paper is about the sled dog Balto, who was partly descended from the Siberian Husky, and was one of the most famous dogs in the world.

In 1925, during an outbreak of diphtheria in Nome, Alaska, Balto helped deliver serum to children. The study examined Balto’s genome and compared it with the genomes of other dogs of that time and the present. It found that sled dogs of that time (including Balto) were genetically healthier than modern dogs, while Balto had more genetic diversity than his contemporaries and also modern dogs.

Genetic variants may be responsible for medulloblastoma

The scientists have found some genetic variants that may be responsible for rare and common human diseases, including cancer. They studied a disease called medulloblastoma. It is a type of brain cancer that originates in the cerebellum, and is the most common type of cancerous brain tumour in children. 

In one of the papers, scientists studied patients with medulloblastoma and found mutations in regions of the human genome which are otherwise conserved across all mammalian species. According to the researchers, these mutations may be associated with the disease, or may slow down the treatment of the illness. 

The fact that the regions are conserved across mammalian species, but show mutations in patients with medulloblastoma, supports the hypothesis that the reason these portions are conserved is because they are important.

Therefore, scientists may use this approach in future to identify genetic changes that could be responsible for diseases.

What other studies found

Other papers have described how some parts of the conserved genomic regions are associated with exceptional mammalian traits such as a superior sense of smell, the ability to hibernate in winters and an extraordinary brain size, among others. 

According to one of the studies, mammals started changing and diverging about 65 million years ago. This was even before the Chicxulub impactor, the asteroid that killed dinosaurs, hit Earth. 

Another study found a link between more than 10,000 genetic deletions in human genomes and the function of neurons. 

One paper said that species that have had a small population size historically are at a higher risk of extinction in the present day.