How does the female’s unfertilized egg know that the sperm entering it is of the wrong species? Is the sperm just unable to enter the egg?
I realize it may be twisted, but there was a joke on Sealab 2021 about a man having sex with an orangutang and producing offspring. Surely this couldn’t happen, but I can’t exactly figure out why.
I’m pretty sure there has to be a very specific chemical signal transmitted by the sperm that the egg is programmed to recognise. Otherwise evolution would have gone haywire long ago.
I would imagine that when the species is close enough, as in dogs and most cats, cross-breeding is easier, but then again I don’t think you could cross-breed a tiger with a house cat. Don’t know why.
I think the problem isn’t the sperm entering the egg, but the DNA being too different to produce a viable embryo.
Most species have different chromosome numbers. If they don’t match up no baby. If they do match up and they are separate species there will probably be a miscarrage because the embryo doesn’t excrete the proper enzyme to keep the mother’s antibodies away from it. One of the execptions of this is with plants or specifically trees. I know they cross breed all the time.
“Consider the ass”
http://www.geocities.com/moredonkeys/aboutmules.html
“If a group of individuals could potentially breed together in the wild to produce fertile offspring, then they belonged to the same species”
http://www.dhushara.com/book/diversit/extra/enig/senig.htm
“Donkey has 62 chromosomes (31 pairs) and Horse has 64 (32 pairs). Thus mule (and hinny) have 63 chromosomes and meiosis during gamete formation is virtually guaranteed to go wrong.”
http://www.biols.susx.ac.uk/ugteach/cws/evol1/rims.htm
Campbell’s Biology, a textbook I happen to have lying around, lists numerous barriers to cross-breeding. The sperm of one species may not be able to survive in the reproductive tract of another. In many species, there are specific molecules on the gel coating of the egg that only a sperm of the same species can adhere to. As stated above,too, if the two species have different numbers of chromosomes, that can prevent hybridization as well. If the sperm does manage to fertilize the egg, many hybrids fail to complete development because their DNA isn’t close enough to create necessary proteins. Finally, some hybrids manage to live, but are unable to reproduce (such as mules).
Yes yes, exceptions do exist to the rule acid, and if you want a REALLY specific answer you’d have to do it species by species as to why they can’t mate.
Listing just a few examples:
Mismatching of the required sexual organs.
Opposite species refuses to answer to improper mating call/act/dance/etc.
The animal in question is actually asexual.
The sperm is not identified by the mother as such.
And even these topics can be broken down into smaller things such as specific enzymes not being present.
But as in almost all biology, there are always exceptions and exceptions to the exceptions and exceptions to the exceptions to the exceptions. But its all about generizations.
Just an interesting article that relates to this a tid bit:
http://news.bbc.co.uk/2/hi/in_depth/sci_tech/2003/denver_2003/2767671.stm
OK, so what’s preventing a human and an orangutang, as in the example that sparked my query, from producing viable offspring? Chromosome counts, inability to survive in the reproductive tracts, egg’s gel coating?
Big one would be what is delicately termed “pre-zygotic isolating mechanisms”. Meaning that we don’t respond to an orangutang’s sexual signals and they don’t respond to ours. How many times have you looked at an orangutang and said “Check out those sexy cheek and throat pads!” It may very well be possible to create a hybrid zygote. I don’t beleive the experiment has ever been carried out, and if it has been carried out no one is advertising that fact.
Actually it has been carried out… Michael Jackson is a bit more than 1/2 man 1/2 plastic…
How about those species which share 99.9% of DNA? Would a Chimpanzilla ever be possible? Or a Manzilla?
Hmm . . . there WAS Bubbles the Chimp . . . who probably shared Jacko’s bed . . . and the result has been hidden away in Neverland.
Seriously, though, I guess that would not be possible, since Neanderthals weren’t able to mix with H. Sapiens and died out as a result.
As shown by mules and hinnys it is possible. For all we know many more crosses are possible but other factors have prevented it.
In this particular case, no it is not possible. For further discussion see:
http://boards.straightdope.com/sdmb/showthread.php?threadid=64664
http://boards.straightdope.com/sdmb/showthread.php?threadid=77064
Just because some closely related species can cross, doesn’t mean all can.
Also, as your link notes, the Biological Species Concept ( species as a group that can interbreed to produce fertile offspring under natural conditions ), though the most commonly cited, has many detractors and a number of exceptions. For example wolves and coyotes will interbreed to produce fertile offspring in the wild and it is likely the “Red Wolf” was one result of such crosses. They don’t commonly do so, but they can and will. Yet for a number of reasons including overall genetic distance from each other as a group ( while having in comparison far less genetic diversity, even over large geographic areas, within either species ), the restricted geographic nature of hybrid zones, the peculiar behavioral nature of such hybridization events ( almost always female coyotes with male wolves, whose offspring cross back with wolves ), and other reasons, they are still considered distinct species.
Hmm, those threads have pretty much said it ALL on this subject . . .
I was not confining the possiblity to outside the test tube.