2 Punten in dit topic.
Naar aanleiding van het topic 16 jarige baby mist ouderdomsgen
ging ik op zoek naar diersoorten die dezelfde genen delen, dezelfde mutaties ondergaan hebben en verschillende effecten daar van ondervonden hebben.
1. Ik vond hier geen artikelen over, als iemand er wel heeft zou ik die graag zien for interest sake.
2. Tijdens het zoeken kwam ik het volgende artikel tegen.
http://www.scientificamer(...)-breeds-same-speciesquote:Full question: How come some similar animals are different species, while with domestic dogs, wildly dissimilar types are considered different breeds?
-- Z. Kornberg, Jerusalem
Michael Bruford, a professor of biological sciences at Cardiff University in Wales, explains the thought process behind this seeming double standard.
Scientists have been distinguishing between species on the basis of how they look, behave or live since recorded history began. However, two famous scientists stand out in terms of how we perceive species differences today: Carl Linnaeus, an 18th-century Swedish naturalist, and Charles Darwin. Linnaeus was the first person to formulate a single approach for describing species in a hierarchical manner according to their similarity, using his binomial nomenclature of genus followed by species (Homo sapiens, for instance). Darwin was among the first people, and certainly the most celebrated among them, to develop a credible theory on how species evolve (via natural selection). Both of these scientists' insights underpin most of what modern science utilizes when studying species and speciation.
Currently species are still primarily distinguished by their appearance, but it is becoming very clear that looks don't always tell us all we need to know about whether two organisms are different. Many so-called cryptic species exist that, to the untrained eye, look very similar or even identical to another organism--commonly found, for example, in nocturnal mammals such as bats and bush babies. If the two mated, however, they may never be able to produce viable offspring; this, in fact, is the primary criterion for dividing similar organisms into different species. Because of these red herrings--and also because the process of describing species is very long and labor-intensive--scientists are increasingly turning to DNA to assist them in identifying and describing species.
Indeed, there is an endeavor under way at the moment called the Barcode of Life project, which aims to sequence all living organisms for a single gene that is common to them all, to produce a species "bar code." The key is that the sequence must vary greatly among species but not vary much within species. Such a bar code can then be used to identify organisms which may not be easily identified (such as tracing back what primate was the source of mysterious smoked meat in the rainforest) and even to distinguish organisms such as microbes that we cannot see or culture in the laboratory. There has been much debate among scientists about which DNA sequence is best for this purpose, and it is likely that a different sequence will work for each different kingdom of organisms. Currently a small gene found in the mitochondrial DNA of our cells--the cytochrome oxidase subunit 1 gene--is most commonly used in identifying members of the kingdom Animalia; a huge database is already in place for many of the world's animals using this gene.
Domestic animals fascinated Darwin and continue to enthrall those of us who own pets. It is certainly curious how domestic dogs, which we know--because DNA bar coding has told us!--were raised by man from a wild gray wolf (Canis lupus) ancestor, can take on such a dramatic variety of forms. But among dogs, which are well known for their hybrid (or mongrel) varieties, different breeds can mate and have viable offspring, so they are all found under the umbrella of a single species, Canis familiaris.
Dogs are highly unusual in their variation, from the Chihuahua to the Great Dane. (Recently, body size was found to be largely explained by differences in a single gene among dog breeds.) Darwin realized that man can force selection by picking particular individuals for breeding who show a particular characteristic that we want to see in our pets. So humans can accelerate the process of selection dramatically by exploiting the diversity naturally found in domestic forms and homing in on a form that is desirable. Natural selection usually acts more slowly, relying on what Darwin described as "descent with modification"--the chance arrival of new forms through DNA mutation. Hierop kwamen een aantal antwoorden.quote:As a biologist I am a tiny bit disappointed in this response.
The article is correct in stating that animals are generally considered different species if they cannot produce viable offspring. More precisely, animals are different species if there is no possibility of their genes being mixed in future generations.
A great dane cannot mate successfully with a chihuahua: it is simply not physically possible. However, Great Danes can interbreed with, say, Border Collies, who can interbreed with Shelties, who can interbreed with Chihuahuas. Consequently, their genes might still be combined in future generations of dogs. So Great Danes and Chihuahuas are not currently separate species. However, they would become separate species if all the medium-sized dogs died out.
This situation, where two groups cannot interbreed directly, but other groups can interbreed with both of them, also occurs in nature. The entire mess is then called a "ring species", and it is one of many natural examples of the speciation process occurring before our eyes. The fact that we have induced the same effect in a domestic animal is really rather thrilling, especially since we have good records of the history of many breeds.
What I am really curious about is, how do creationists deal with the existence of dogs? Do they think chihuahuas and great danes are different species, separately created? Or do they think chihuahuas and great danes can interbreed?
Or do they just... not think? quote:This may be a dumb question, but if the criteria of whether or not dogs are part of different "breeds" instead of "species" is based on if they can create viable offspring, then why are wolves considered a different species? Can't wolves and dogs interbred? quote:Well kids, this is a very wrong answer. Domestic dogs of many varieties interbreed well with wolves, and the results are fertile and breed true. Lots of the USMC dogs are wolf/shepherd hybrids. They're crossbred with other working dog varieties, too, including dobermans, rottweilers, and weimeraners. To be honest, most people can't tell the wolf from the shepherd by looking, and the hybrids are just big smart dogs that get sick a little less than the purebred "dog". Personality wise, some would rather bite you than smell you, and others are just big teddy bears. I think there's some kind of genetic behavior trait that's 50/50 in the crossing.
As for a chihuahua not able to breed with a great dane, that's just wrong too. True, a dane sire with a chihuahua bitch is going to have problems as the pups will grow too big for natural delivery. But I've seen male chihuahuas mount some pretty big females (heck, I saw a little ratdog humping a camel once, although I don't think the camel noticed, and I'm pretty sure there were no offspring), and you could always fall back to AI. The thing is, the breeding would be likely to take, and you'd have some pretty strange puppies -- probably stupid and as mean as hell from what I know about chihuahuas, but you can never tell.
Dingoes are considered another species too, but they breed with dogs and wolves just fine, though the pups bark funny. And in the southwest US, coydogs (coyote/dog hybrids) show up from time to time, and they are fertile even though coyotes have major reproductive differences from dogs. And they're 50/50 on crazy, too.
Nope, the reason different breeds of dogs are considered the same species and wolves are something else is partly historical and partly political. After all, if we recognized the physiologically distinct chihuahua and great dane as different species, we'd have to recognize asian, negro, and caucasians as different species, and that's something that Political Correctness cannot countenance. Which is a shame, since we know the different human breeds have very different medical, dietary, and social issues to contend with, but science is "racist" if it tackles the problem that way.
And if we went the other way and claimed wolves and dogs to be the same species, then we'd have to deal with the issue that we smart humans didn't succeed in making the wolf into a new species after all.
We are not as smart as we think we are. Ik vind dit een interessant antwoord.
Zou graag jullie mening hierover horen.
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