外生殖器的演化與發生

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Evolution and Development of External Genitalia

The term “development” 發生 (sometimes translated as 胚胎發育 in Taiwan) is used in embryology 胚胎學.

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Elizabeth Pennisi, Mystery Solved: Where the Penis Comes From. Science, Nov 5, 2014 (in the category "Latest News").
news.sciencemag.org/biology/2014/11/mystery-solved-where-penis-comes
(“In snakes and lizards, the penis arises from what will become—or, in snakes, would have been—the beginnings of the back legs, whereas in mice, some of the cells destined to become the tail take on that task. Penis formation in the chicken involved cells from the would-be tail and the would-be hindlimb, the team reports. What was common to all of these animals was the role of the cloaca 泄殖腔, a cavity destined to become the lower part of the gut. Signals from the cloaca initiate penis formation in each animal”)

My comment:
(a) The news was not published in press when the latest Science magazine was dated Nov 7. Thus I do not have its volume and page number, if it is ever published in print.
(b) The quotation is agreed upon by the two research groups mentioned in this news, which went on to state,

“The two groups agree that the cells that form the penis start out at the outer edge of the embryo and that they are closer to the tail in the mouse and chicken than in the snake. But they don’t agree on whether those first cells are part of the pool of cells destined to become a limb or tail or whether the cells belong to a separate, nearby pool that is already specialized to become the penis. ‘I think they are adjacent populations,’ Cohn says.

(c) The rest of the news can be explained by the two groups of different opinions.

The Harvard group contends, as the news reported:
(i) “But as in real estate, location is everything. The rodent cloaca is back by the tail-to-be and taps some nearby cells for the penis [or clitoris in a female], whereas the snake cloaca is close to where two limbs used to sprout. Hence, the snake [and lizard, both of which form the order of Squamata. See the last posting] gets two penises [officially called hemi-penises--or hemi-clotorises in a female] instead of just one
(ii) and, “When the researchers attached cloacal tissue to other parts of the chick embryo, they saw the buds indicative of penis growth where they should not have otherwise formed. They did not let the chick develop beyond this point.  ‘Wherever you put the cloaca, that determines what cell types you recruit,’ Tschopp explains.

The Harvard observation that penis buds appear everywhere the transplanted cloaca is, underpins its conclusion that “those first [genitalia] cells are part of the pool of cells destined to become a limb or tail.”

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Tschopp P et al, A Relative Shift in Cloacal Location Repositions External Genitalia in Amniote Evolution. Nature, _: _ (online publication Nov 5, 2014).
www.nature.com/nature/journal/vaop/ncurrent/full/nature13819.html

Note:
(a)
(i) The first author Patrick Tschopp is a postdoctoral fellow in the lab of professor Clifford J Tabin.
(ii) The Swiss German surname Tschopp signified “a jacket maker, from Middle High German jop(p)e, juppe ‘jacket’ (schope, schoppe).”

(b) Only a subscriber (individual, or organization such as school) can read the entire article online. (Though informative, the article itself does not say a lot. So you need not read it.) For those you can access the article, legend of Figure 1 explains the plane of micro-computed-tomography (μCT). And “highlighted in [fetus] sketch in white” shows the arc of the fetus of four species in Figure 1, a-d.

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Ana M Herrera & Martin J Cohn, Embryonic Origin and Compartmental Organization of the External Genitalia. Scientific Reports (a Nature publication), _: _ (online publication Nov 5, 2014).
www.nature.com/srep/2014/141105/srep06896/full/srep06896.html

Note:
(a) Ana Maria Herrera Leon (Leon being the married--or husband’s--name) was a PhD student from 2008 to December, 2013 (according to LinkedIn).

(b) If you can access the article (and I have reasons to believe you may), both read Introduction and view Figure 6.
(i) The first sentence of Introduction remarks:

“Congenital defects of the external genitalia occur at a remarkable frequency in humans, with hypospadias (incomplete closure of the urethral tube) affecting ~1:250 live births.”

For hypospadias (Latin, from Greek; hypo- + spadias) 尿道下裂, view only graphics and photos in
en.wikipedia.org/wiki/Hypospadias
(ii) The methodology is, injecting a fluorescent dye into a genital swelling--which the authors sometimes call “external genital progenitor pool”--to monitor its moving toward the center (and fuse with genital swelling from the other side, in all land animals except squamates.
(A) Squamata
en.wikipedia.org/wiki/Squamata
(The Squamata, or the scaled reptiles, are the largest recent order of reptiles, comprising all lizards and snakes)
(B) Squamata (n; from Latin [adjective masculine] squamatus “scaly, having scales”, from [noun feminine] squama “scale”)
en.wiktionary.org/wiki/Squamata