The gene mutation contributing to the diminutive size of 'toy' dog breeds existed in wolves 54,000 years ago.

Long before humans began selectively selecting cute canines, it was already present.

 

Some dog breeds, including Pomeranians and Chihuahuas, are small because of a genetic abnormality that first appeared in distant ancestors of dogs long before humans started breeding them. According to the study's authors, the mutation has been traced back to wolves that existed over 50,000 years ago.

 

The mutation in the insulin-like growth factor 1 (IGF1) gene was uncovered by analyzing data from the National Institutes of Health (NIH) Dog Genome Project, a citizen science initiative in which dog owners submit DNA samples of their canine companions for scientific investigation. The existence of this "unique" mutation, which was discovered not in the IGF1 gene but in DNA that controls the expression of this gene, had been hidden from scientists for over a decade.

 

Scientists from England and Germany helped confirm that the mutation was present in 54,000-year-old DNA from fossils of Siberian wolves (Canis lupus campestris) and that it is present in the DNA of all living canid species, including jackals, coyotes, and African hunting dogs.

 

Senior author Elaine Ostrander, a geneticist at the NIH who specializes in dogs, said, "It's as though nature had kept it tucked in her back pocket for tens of thousands of years until it was needed." She said this finding helped bring together previous research on canine domestication and body size.

 

The mutation is out of the ordinary.

 

Genes are segments of DNA that serve as instructions for making particular proteins. A gene is the set of instructions for making a specific protein, and it consists of a specific sequence of four bases called adenine, guanine, cytosine, and thymine. Cells must unzip the double helix of DNA to read the nucleotides of the gene encoding a certain protein. DNA is copied by specialized machinery within the cell to produce RNA, a single-stranded molecule similar to DNA but for one sugar (ribose instead of deoxyribose) and one base (uracil (U) instead of thymine (T)). RNA is subsequently utilized to produce proteins. Transcribing something is what it sounds like.

 

The novel mutation affects the gene expression close to the IGF1 gene, affecting the dog's size. Ostrander told Live Science that there are two variants of this DNA sequence, or allele, one of which contains an extra cytosine base (C), which results in lower body size, and the other has an extra thymine base (T), which results in larger body size. Since each dog receives one copy of the gene from each parent, it is possible for a dog to have two copies of the small allele (CC), one copy of each (CT), or two copies of the large allele (TT).

 

When studying the genetic makeup of several dog breeds, scientists discovered a striking pattern:

* Little dogs tended to have the CC allele.

* Medium-sized dogs had the CT allele.

* Large dogs had the TT allele.

 

Constantly diminishing

 

After discovering the mutation, NIH scientists were curious about the evolutionary history of the alleles it represents in canids, so they looked for it in the genomes of extinct wolves that had already been published.

 

According to Ostrander's interview with Live Science, "we were startled to uncover the mutation and happy to realize that both variations [C and T] were there over 54,000 years ago." However, contrary to what the researchers had hypothesized, she explained that the allele for shorter stature was not more recent than the allele for taller stature.

 

Jackals, coyotes, and African hunting dogs are smaller than domestic dogs because they carry two copies of the small allele for the IGF1 gene (CC). However, she noted that it's highly improbable that little dogs would have naturally developed into their present-day diminutive stature absent the influence of human domestication and selective breeding.

 

For "tens of thousands of years," Ostrander says, "the tiny allele was preserved at a low level" in dogs, only to be "selected on" some time "at or around the time of domestication." She explained that the breeding was done to produce smaller dogs more suited for hunting rabbits and other small game.

 

Researchers estimate that between 7,000 and 9,500 years ago, the first somewhat smaller dog breeds appeared; these dogs were further developed into the exceedingly diminutive variants we see today.

 

Acquiring an Apprehension of Size

 

There are more genes besides IGF1 that influence canine size. At least 20 genes are known to encode for body size. Still, this one has a disproportionate impact: According to Ostrander, this one gene accounts for around 15% of the variation in canine body size across breeds.

 

Ostrander claims that hundreds of genes influence human stature. However, she added, it shouldn't come as a surprise that dogs have fewer body-size-related genes than humans, given that most canine breeds have only been around for a few hundred years.

 

The research team plans to explore even more canine to learn how the genes for canine body size interact to produce the wide range of sizes seen in dog breeds, from miniature Chihuahuas to giant Great Danes body-size genes in the future. Ostrander has indicated that the next stage is to determine how the many proteins generated by these genes interact to produce various sizes and breeds of dogs.

Reference : https://www.livescience.com/small-dog-gene-found-in-ancient-wolves

Image source : https://pixabay.com/id/illustrations/serigala-bulan-pohon-siluet-647528/

# The same gene mutation that led to the tiny stature of 'toy' dog breeds first appeared in wolves 54,000 years ago.

# 54,000 years ago, wolves had a gene mutation that contributes to the small size of modern "toy" dog breeds.