有什麼理論能說明，如今要讓雞長六隻翅膀是不是可能的？

01-04

讓雞長六隻翅膀在理論上是完全可行的。

下方有大量配圖可能引起不適

自然中如果胚胎髮育異常，是會出現這種現象的，英文polymelia. 答案最後copy了一些動物多肢現象的圖。

人工誘導多肢也是有的，下圖是肢發育的過程，基本上是通過生長因子 FGF推動肢芽向外延伸(outgrowth)，而信號因子Shh促進FGF表達。

生長因子 FGF 在圖中AER（apical ectodermal ridge）的位置起作用。事實上，很多胚胎實驗是以雞作為模式生物的，雞翅的結構見下圖，由於很好辨認各個趾（digit），可以很快而準確地檢測胚胎的肢是否發育正常。

現在有意思的地方來了，有人做了實驗，Niswander et al. (1994)，Cohn MJ et al 1995, 如果把一個浸泡了FGF的緩釋球(beads)植入雞胚胎體內，注意看下圖左第一幅，胚胎右側多出來的一個黑點就是FGF緩釋球誘導形成的一個AER(類似於肢芽前體)，然後形成了一個完整的翅膀。

因此，理論上6個翅膀的雞是可以通過FGF緩釋球誘導出來的。但是這種方法，能不能大規模商業應用，是否收益高於成本，以及有什麼樣的食品健康和倫理風險就超越了這個答案本身了。

AER的詳細解釋

（A feedback loop between the AER and the ZPA. Shh is expressed in the ZPA in the posterior mesoderm of the limb bud. FGF4 is expressed in the posterior AER, while FGF8 is expressed throughout the AER. The continued expression of Shh depends on FGF signalling, while the expression of FGF4 requires Shh signals. Together, the ZPA and AER pattern the anterior–posterior and proximal–distal axes of the vertebrate limb.

From: Limb Development

source:FGF Signalling in Vertebrate Development.Pownall ME, Isaacs HV.

）

多肢現象枚舉

http://psycheskinner.hubpages.com/hub/Duplicate-Limbs

Polymelia: Animals with Duplicate Limbs:

There are many different conditions that can cause animals to be born with extra limbs--a condition called polymelia. Some examples are described below. The main causes of extra limbs is the partial development of a conjoined twin, of a genetic mutation (spontaneous or inherited) that affects fetal development. It can also occur due to the effect injuries, toxins and/or infections during crucial periods of fetal development.

Cattle

There are quite a few examples of cattle that survive in good health with extra legs. The extra limbs often remain small and vestigial, allowing the bull or cow to function in a normal manner.

However they can also be large or comprise of up to seven legs and other body parts. Or cases like this one from 1981 which are more disabling to the calf, as the extra limbs diverge at the "knee" rather than higher in the body, and so impede locomotion and normal body postures.

Polymelia in cattle is sometimes found to be associated withchromosomes having multiple breaks. In other cases is results from an incomplete conjoined twin.

For further examples see: Japan (1985), Brazil (2008), Cambodia (2003) (shown right), United States/Nebraska (2007), India (2010), India (year unknown)

Deer

In 2008 a six-legged fawn was found. The fawn was separated from its mother and rescued when it was found under attack from dogs.

As with many of the examples in cattle, the extra limbs belonged to a partially developed conjoined twin. In general, this condition seems to be especially rare in deer.

Dolphin

This dolphin, caught off the coast of Japan, was documented to have an extra set of fins (2006). This abnormality was though to reflect that dolphins evolved from species that has hind legs. These fins are not really an abnormality, but may be cause by a mutation that activated a feature that was carried by the dolphins evolutionary ancestors, but is not normally expressed in modern dolphin. Fins of ths type are reported to occur occassionally and various species of dolphin and whale.

Frogs

Deformities, including extra limbs, are being seen more often in frogs around the world. Different explanations have been offered for these deformities including the effects of pollution, hormones or climate change. The preferred explanation now is that deformities are produced when parasitic wormsinfect tadpoles.

Dogs

In 2009 a puppy with an extra legwas given surgery to remove the extra limb and avoid the animal being displayed in a modern freak show. The six-legged puppy shown to the right was discovered as a stray in 2005.

For other examples see: Italy (16th century), Ukraine (preserved specimen, 2009), United States(2009)

Cats

A six-legged kitten born in Florida(2006) but infortunately died during surgery to remove the limbs.

Victorian taxidermy also gives us this example of an eight-legged kitten.

Poultry

Poly melia has been observed intermittantly in chickens. A case was described in a slaughterhouse in 1985 and a four-legged chick was hatched in Australia in 2010.

In 2007 a fourlegged duck was hatched in the United Kingdom. However due to an accident"Stumpy" (right) ended up losing one extra leg. Another seemed to break off naturally. Thus Stumpy ultimately ended up living life as a conventioned two-legged duck.

Sheep

In 2002 the shown to the right sheepwas born in the Netherlands with a fifth leg. Polymelia is a defect considered not uncommon in sheep.

Other examples include: New Zealand (2007), Unknown location(2009), Skeleton: Fragonard Museum, Paris (year unknown).

Swine

Duplicate limbs occur very rarely in pigs. One example known from 2008 had two extra hing legs and may be the result of an extremely underdeveloped conjoined or parasitic twin. Other examples include: China (year unknown).

你想讓它飛向銀河系咩？