Half Breeds: An Overview of Crossbreeding Species

The following is an article from the book Uncle John's Bathroom Reader Plunges Into the Universe.

The Snortgurgle. (Image credit: Billertl)

What do you get when you cross a goat with a spider? You’re about to find out.

Let’s make this simple.  By and large, you can’t breed one species of animal with another. You can’t just shove a goat and a kangaroo in a room with mood lighting and Barry White albums and expect baby goat-a-roos to hop out a few trimesters later. The reason for this is the reason that there are different sorts of animals in the first place. It’s called speciation, and it occurs when a population of animals, for various reasons, evolve to a point where they can’t interbreed successfully with other related animals (“success” in this case meaning making more of themselves).

They're just snuggling for fun. (Image credit: The Pet Collective)


This can happen when an animal population is cut off from other animals like it and adapts to its new surroundings (“adaptive radiation,” which has nothing to do with plutonium), or when a random mutation spreads through one group of animals, eventually cutting it off genetically from other animals to create a new species (“quantum speciation,” which has nothing to do with quarks and leptons). Once you’re in a new species, that’s pretty much it. Genetically speaking, you stick to your own kind.


The Wolpertinger. (Image credit: Rainer Zenz)

Humans, who are either ignorant of the complexities of the genetic process of speciation or -as is so frequently the case- not willing to let a simple thing like evolution get in the way of their fun, have tried over the millennia to mix and match their animal species to see what they can get out of it. (Usually, two agitated animals that want nothing to do with each other.)


Chihuahua and Great Dane. (Image credit: Elf)

The one reason to do this is to take advantage of a concept called “hybrid vigor” -the idea that the interaction of genes from two different animals will make the resulting animal hardier than either parent. This has been proven to work between different breeds of a single species. Humans have been breeding dogs this way for hundreds of years to accentuate desired traits, giving us a species of animal whose sizes range from a Chihuahua to Great Danes (theoretically, you could breed a Chihuahua with a Great Dane, although, depending on which is the male and which is the female, the process could be either painful or humiliating).


The success of mixing different species of animals are few and far between. The single most successful example of a species crossbreed is the mule, which is what you get when you cross a male donkey or ass (also known as a “jackass’) with a female horse (a mare). Humans have been breeding mules as pack animals for over 3,000 years. Almost all mules are sterile. Incidentally, if a female donkey and a male horse breed, the resulting offspring is called a “hinny.” Hinnies are considered to be less hardy than mules, so there isn’t much call for them.


(Image credit: Andy Carvin)

Another famous crossbreed is a “liger,” which is what you get when you breed a male lion and a female tiger (female lions and male tigers -you get a “tigon”). Ligers and tigons are exclusively created through human meddling, since lions and tigers in the wild don’t share much in common in terms of habitat or behavior (lions live in groups, tigers work alone). Like mules, ligers and tigons are almost always sterile, although there have been cases of females who are able to breed.


The zorse named Eclyse. (Image credit: Flickr user
uri press GmbH)

In the case of mules and hinnies, and ligers and tigons, the crossbreeding takes place within species families. Horses and donkeys belong to the same genetic family of species called Equidae (which also includes zebras, which are sometimes bred with horses to create -wait  for it- “zorses”), while lions and tigers are in the family Felidae, which also includes cheetahs, pumas, leopards, jaguars, and your own domestic housecat (attempting to breed your cat with a lion or tiger is a fine way to get your cat eaten, so don’t do it). There’s been no successful attempt at crossbreeding species outside genetic families. No crossing horses and tigers, or bears and dolphins, or whatever.


That is, not until humans began to master the art of genetic manipulation. Now that humans have begun to crack the DNA code, we’ve started to mix and match genes from one animal species with others, creating genetically engineered animals with genes that span not just genetic families, but across entire animal phyla.


(Image credit: Klearchos Kapoutsis)

For example, in an attempt to generate massive amounts of spider silk that could eventually be used to create superstrong fabrics, scientists have taken genes from orb weaver spiders and placed them into goats, which then produce spider web proteins in their milk, which can in turn then (theoretically) be processed out. The goats look and act like normal goats -no eight-legged goats spinning webs or cocooning the scientists in silk to eat them later (at least not yet)- but they’ve go just a little bit of spider in them.


Scientists have high hopes for the “transgenic” animals. Plans are underway to creat cows or goats that are genetically engineered to produce medicines in their milk. Other transgenic animals are of somewhat more dubious utility, unless you can think of a good reason for putting jellyfish DNA into mice, as a bunch of Caltech researchers did, which made the mice glow green under fluorescent lighting.

Fluorescent mice. (Image credit: Ingrid Moen, Charlotte Jevne, Jian Wang, Karl-Henning Kalland, Martha Chekenya, Lars A Akslen, Linda Sleire, Per Ø Enger, Rolf K Reed, Anne M Øyan and Linda EB Stuhr)


One major difference exists between transgenic animals and their traditionally crossbred brethren. Transgenic animals pass on their genetic traits to their offspring -the CalTech researchers noted that the offspring of the jellymice had the same fluorescent gene as their parents. Given the pace of genetic development, owning your own glow-in-the-dark transgenic pet may not be too far in the future. Just don’t try to crossbreed it with your cat or dog (or your horse). Leave that stuff to the pros.


The article above was reprinted with permission from Uncle John's Bathroom Reader Plunges Into the Universe.

Since 1988, the Bathroom Reader Institute had published a series of popular books containing irresistible bits of trivia and obscure yet fascinating facts.

If you like Neatorama, you'll love the Bathroom Reader Institute's books - go ahead and check 'em out!

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Having posted a few glow-in-the-dark animal experiments, we know the reasons for them. First, because it's an easy way to see if your gene-splicing techniques work. Then, it became a way to mark certain genes in the DNA sequence to pave the way for other, more useful gene-splicing experiments.
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