Remember corny kids' jokes like these?
What do you get when you cross a turtle and a porcupine?
Answer: A slow poke.
What do you get when you cross a fish with an elephant?
Answer: Swimming trunks.
Well, when we were kids, thinking that people could actually cross one animal with another very different animal seemed totally preposterous. In today's world, however, genetic engineers are doing just that.
For example, you probably never thought scientists could cross spiders with goats, but now it's being done.
Researchers found a way to put spider genes in Nigerian dwarf goats. Milk collected from these genetically altered farm animals contains spider silk protein that can be collected, purified and spun into synthetic spider silk fibers.
Real spider silk, the kind spiders use to weave their webs, is stronger than Kevlar, which is used in bullet-proof vests, stretches better than nylon and, weight for weight, is five times stronger than steel.
The artificial silk refined from the goat milk mimics these properties and is being touted for use in automotive and aerospace components, high-tensile-strength medical sutures, artificial tendons, lighter body armor for law enforcement and military, and even get this biodegradable fishing line.
How about a pig crossed with a rodent? It's been done.
The resulting animals, dubbed "enviropigs," have a gene made from the E. coli bacterium along with mouse DNA. The extra gene helps the pigs produce an enzyme in their saliva that sharply reduces the pollutant phosphorous in their manure.
Scientists in Japan have even inserted genetic material from spinach into pigs, which they say will produce healthier pork with less fat.
For years, mammals were the subjects of most bioengineering projects. Now fish have become the focus for many scientists.
Have you heard about the GloFish, the world's first genetically engineered pet? Scientists took the zebra fish, a popular aquarium fish, and made it glow in eerie colors (Starfire Red, Electric Green or Sunburst Orange) by injecting jellyfish or sea anemone genes into zebra fish eggs.
These "transgenic" fish fluoresce under a traditional white aquarium light during the day and under a black light at night.
The researchers who created GloFish wanted to produce a fish that could help fight water pollution. To do this, they added a "switch" they hoped would cause the zebra fish to glow in the presence of environmental toxins.
A non-fluorescing fish would signal the water is safe, while a fluorescing fish would signal trouble. Although these fish are currently unavailable, scientists hope to complete this work soon.
Glowing mice, insects and rabbits also have been created in laboratories. Other glowing fish may soon be available, such as carp and goldfish.
Scientists also have been tinkering with some of the fishes we enjoy catching on hook and line, primarily those species raised in aquaculture operations for food.
For example, genes from the ocean pout, an ugly bottom-dwelling fish that resembles an eel, have been transplanted into Atlantic salmon. The pout gene allows the salmon to produce growth hormones year-round, instead of just during warm months, so it grows five times as fast as a normal farm-raised salmon.
These transgenic salmon reach marketable size much faster and do so with 10 to 25 percent less food. It's like tuning up your car. Instead of 10 miles per gallon, in the early stages, it gets 40 miles per gallon.
Similar results were obtained by modifying the growth hormone gene in coho salmon using genes derived from sockeye salmon. The transgenic coho grew on average 11 times faster than unmodified fish, and the largest fish grew 37 times faster.
Making fish more disease resistant is another aim of bioengineers. To do this, U.S. scientists transferred silk moth genes to channel catfish. These genes function as built-in fungicides and bactericides. Chinese researchers placed a human interferon gene into grass carp for the same reason. That's right: a human-fish cross!
Another coming attraction is goldfish that are more cold-resistant due to the insertion of antifreeze protein genes from Arctic fish such as the winter flounder. If this works, those expensive koi in your garden pool won't turn belly-up this winter, even if the pond freezes over. And if you use goldfish for fish bait, you'll probably be able to keep them fresh and alive on ice.
Other fish that have been genetically engineered include largemouth bass, northern pike, rainbow trout, sea bream, striped bass, tilapia and walleye. There seems no end to the possibilities.
Not surprisingly, however, many people are concerned that transgenic fish may be unsafe for people and the environment. Scientists are sharply divided in their views.
Some experts regard such fish as the potential answer to the depletion of the world's fisheries and a practical way to increase protein intake for many malnourished people.
Increasing production of farm-raised fish, they say, could relieve the strain on wild populations pressured by overharvest. They believe that even if some fertile bioengineered fish manage to escape to oceans or freshwater bodies, the fish will not pose a severe ecological hazard.
Others believe genetically modified fish could permanently eliminate many species of wild fish by diluting the wild gene pool. Whole ecological systems could be at risk if transgenic fish prey on and outcompete native species, as many introduced exotic fish have done.
No doubt, this debate will rage for decades. And while it does, some amazing things that could happen probably won't happen. Nevertheless, it's interesting to speculate on possibilities.
Could we, for example, create strains of bioengineered fish that grow to enormous sizes? Would it be possible to splice striped bass genes with largemouth DNA to produce a 50-pound bucketmouth?
Could a whale shark be crossed with a flathead to grow a catfish that weighs a ton or more?
Will bluegills the size of hub caps and brook trout as big as king salmon swim the lakes and rivers of the future?
If we took the antifreeze genes from winter flounder and put them in Brazilian peacock bass, the peacocks would be cold hardy. Then we could stock our ponds with them and enjoy those explosive strikes year-round without traveling to Florida or South America.
Maybe we could make prettier fish, too. I'd like to see a zebra bass with beautiful black-and-white stripes or perhaps a jaguar bass with spots. We could give ugly fish like bowfins and sturgeon a makeover by crossing them with multi-colored butterflies or songbirds.
Speaking of birds, I wonder if it would be possible to cross game fish with our feathered friends to create new kinds of flying fish. Imagine an eagle-marlin hybrid. When it jumped, it would soar away with your ballyhoo, compounding the thrills of the fight.
And consider the possibilities of crossing parrots and sport fish. Could we create talking fish? What would they say?
"Polly want a crankbait."
I'd like to see a walleye implanted with genes from a Holstein milk cow so the fillets would be full of butter and ready to sauté for a shore lunch.
Glow-in-the-dark fish would be neat, too. If we can use jellyfish genes to make GloFish, why not use them to light up our lakes with GloBream or GloCrappie? Better yet, how 'bout some GloMinnows we could use for night fishing?
Of course, we'd have to be careful with these experiments or we'd wind up like the folks in the 2004 movie "Frankenfish." This story pits a pack of huge, mutant, flesh-eating fish against the human inhabitants of a bayou town.
A genetic-engineering experiment gone horribly awry, these monsters are the result of a cross between a fish and a snake, and can travel on land as well as swim. They have a taste for blood, leaving a trail of gruesome corpses up and down the river.
I wonder what it would be like to hook one of those.