Freethought & Rationalism Archive

HumanisTim · 07-31-2002, 05:39 AM

1. I'm not talking about if this would be ethical. But if it would be possible. Would it be possible to alter an embryo's genes or an egg or sperm cells. And reactivate all the recessive genes and cause a person to give birth to a Australopithecus type creature. This feels like a dumb question. But I thought it be worth asking.

2. Are there any combinations of dogs which can not geneticly*sp* cross breed. I don't mean stuff like it not being practical like a great dane and toy poodle. I mean geneticly unable to breed.

3. And last but not least does evolution have anything to do with the disorder of Down's syndrome. and Does Down's syndrome appear anywhere else in the animal kingdom besides humans.

Thanks to anyone who can answer these.

scigirl · 07-31-2002, 06:37 AM

Quote:

Originally posted by Tim Sweitzer:
Would it be possible to alter an embryo's genes or an egg or sperm cells. And reactivate all the recessive genes and cause a person to give birth to a Australopithecus type creature.

It wouldn't be a matter of activating all the 'recessive genes,' it would be a matter of recreating the genes, and their expression patterns, to create said organism. If evolution is correct, I think the answer is "yes." However we have a long way to go to determine what alterations would be necessary to do this.

Quote:

2. Are there any combinations of dogs which can not geneticly*sp* cross breed. I don't mean stuff like it not being practical like a great dane and toy poodle. I mean geneticly unable to breed.

I haven't heard of any. Oolon or someone else may know.

Quote:

3. And last but not least does evolution have anything to do with the disorder of Down's syndrome.

Doubt it - most Down's syndrome people are infertile.

Quote:

and Does Down's syndrome appear anywhere else in the animal kingdom besides humans.

I'm sure it does. Down's syndrome is called a "trisomy" - during meiosis, the pairs of chromosomes fail to divide correctly, leaving one sperm or egg with one copy, and the other with three (trisomy). Most trisomies are fatal, and the woman has a miscarriage. Trisomy of human chromosome 21 appears to be survivable, as do trisomies or monosomies of the sex chromosomes. This happens in animals, although it obviously has different symptoms. <a href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=118404 89&dopt=Abstract" target="_blank">Here's</a> a mouse model of Down's Syndrome, but in this case, the chromosome number 16, not 21:

Quote:

The Ts65Dn mouse, which has segmental trisomy 16, producing dosage imbalance for about half the genes found on human Chr 21, exhibits specific skeletal malformations corresponding directly to the craniofacial dysmorphogenesis in DS. Here we demonstrate that Ts1Cje mice, which are at dosage imbalance for about 3/4 of the genes triplicated in Ts65Dn, demonstrate a very similar pattern of anomalies in the craniofacial skeleton. However, one characteristic of Ts65Dn mice, a broadening of the cranial vault contributing to brachycephaly, is not seen in Ts1Cje mice.

scigirl

nogods4me · 07-31-2002, 06:41 AM

a variation on the original question might be: Is it possible to reactivate, or repair the gene we have that used to produce vitamin C? Could we give injections to expectant mothers that would be able to restore funcionality to that gene? no more scurvy.

Oolon Colluphid · 07-31-2002, 07:32 AM

Ref the dogs, I�ve not heard of anything except the physical practicalities of great danes x chihuahuas etc. But that could be enough. There�s two things to bear in mind.

1) Closely related species (as sufficiently diverse dogs would be) can and do interbreed. Mallards and pintails, lions and tigers, llamas, camels and vicunas, and a range of butterflies (I�ll check which if you like) spring to mind; Mr Darwin can doubtless suggest plant species. And there�s ring species such as Ensatina salamanders and Larus gulls, which interbreed all round the geographical ring, till it meets, where they don�t. Whether or not the offspring are fertile is almost beside the point, and brings me to...

2) Morphological difference (eg here, size of genitalia) is just one of a host of reproductive barriers between species. If we go (for simplicity) with the Biological Species Concept, then a species is simply a bunch of organisms that can interbreed among themselves, but not with anything else. Speciation is therefore the evolution of reproductive barriers, of isolating mechanisms. There�s barriers both before and after mating.

Pre-mating ones include variations in courtship rituals, scents and calls, size or shape of genitals, and timing of reproductive cycles. Post-mating ones are things like hybrid inviability (embryo doesn�t develop properly), or hybrids (and remember, we�re all hybrids -- of our parents� genes) which develop to healthy adulthood, but which may have any degree of infertility, such as horse x donkey making sterile mules and hinnies.

So we find in nature a full range of situations, from fully interbreeding, to don�t �want� to interbreed but could, to production of healthy but sterile offspring, to don�t interbreed and nothing comes of it even if they do. And several of the steps have been observed to evolve (by �microevolution�, of course

).

Being genetically incompatible, which Tim asks about, is almost irrelevant: mere courtship rituals keep mallards and pintails separate in the wild, but fertile offspring can be produced in zoos. Northern and southern leopard frogs happily interbreed, but the embryo fails to develop correctly, and it seems it�s just a case of each half of the genetic recipe requiring different 'cooking' temperatures. That�s a genetic incompatibility, but it�s based on only a small difference, and an environmental not a genetic one at that. Speciation is all a matter of degree of isolation -- which is what evolution predicts -- and isolation can take many forms.

So with dogs, my humble layman�s opinion is that big and little dogs are potentially separate species. There�s both pre- and post-mating barriers (genitals don�t fit, and the severe difficulties of birthing pups from a big male dog / little female dog cross. If medium-sized dogs were wiped out, they would de facto be separate species. But since there can be gene flow via the medium-sized dogs, I guess they�re still one species. It�s more like the ring species situation, with it unclear whether they�re one species or two.

Hope that helps.

Cheers, Oolon

[ July 31, 2002: Message edited by: Oolon Colluphid ]

theyeti · 07-31-2002, 07:56 AM

Quote:

Originally posted by nogods4me:
a variation on the original question might be: Is it possible to reactivate, or repair the gene we have that used to produce vitamin C? Could we give injections to expectant mothers that would be able to restore funcionality to that gene? no more scurvy.

Theoretically, yes. But it would require replacing the broken gene with a new one, and so it wouldn't be a matter or "repair" so much as "replacement". In other words, the presence of the broken gene would make no difference -- the new gene would be inserted somewhere more or less at random. However, it's likely that the functional gene has to be regulated in some way, so we would also have to include regulatory elements with the gene therapy, which is probably beyond current technology. Why someone would want to do it is beyond me -- it's much cheaper and easier to give people vit. C suplements. The only people who get scurvy are much too poor to afford advanced gene therapy.

theyeti

Dr Rick · 07-31-2002, 08:36 AM

All domestic dogs, wolves, coyotes, and jackals can mate with each others (barring size constraints) to produce viable and fertile offspring, but not with foxes because foxes have different numbers of chromosomes than the others.

Rick

Oolon Colluphid · 07-31-2002, 08:52 AM

Quote:

Originally posted by rbochnermd:
All domestic dogs, wolves, coyotes, and jackals can mate with each others (barring size constraints) to produce viable and fertile offspring, but not with foxes because foxes have different numbers of chromosomes than the others.

Rick

Interesting... I didn't realise about jackals. I wonder about African hunting dogs...? And whether domestic cats could reproduce with things like sand cats (Felis margarita, see <a href="http://www.marwell.org.uk/n2002-07-11a.htm" target="_blank">http://www.marwell.org.uk/n2002-07-11a.htm</a> )...?

Oolon

hyzer · 07-31-2002, 08:53 AM

“Would it be possible to alter an embryo's genes or an egg or sperm cells? And reactivate all the recessive genes and cause a person to give birth to a Australopithecus type creature.”

I once posted (on II if I remember correctly) that this very scenario would make a great work of fiction (ala Jurassic Park) – scientist discovers DNA altering breeding method by each new generation is actually a step backwards into the evolutionary history of that species, scientist breeds proto-bacteria, then proto-mice, perfects the method in which each step is bigger and bigger, further into the past, goes mad when the human experiments succeed . . . (but fundamentalists protest that the resulting creatures “don’t prove evolution” ).

Late_Cretaceous · 07-31-2002, 09:26 AM

" except the physical practicalities of great danes x chihuahuas etc"

It sure does not stop them from trying. I once saw a tiny male dog (breed=?) trying desperatly to mate with a large female German Shepard. She was actually trying hard to accomodate him, but try as he might he just could not mount her. Finally, he gave up in frustration, lay on his side and blew his load.

SO, I think you are correct to say that size is a reproductive barrier that could potentially get bigger with generations until they become separate species. I suppose this could happen if a population of island dwarfs of some animal were reintorduced to the mainland.

[ July 31, 2002: Message edited by: Late_Cretaceous ]

Late_Cretaceous · 07-31-2002, 09:31 AM

WOuld mitochondria from distantly related species work in each other's cells? If you could kill the mitochondira in all the cells of a human, then replace them with mitochondira from a shark, would it work (assuming the technology to do it worked of course)?

07-31-2002, 05:39 AM	#1
HumanisTim Regular Member Join Date: Feb 2002 Location: Reading,PA Posts: 233	Couple of Questions 1. I'm not talking about if this would be ethical. But if it would be possible. Would it be possible to alter an embryo's genes or an egg or sperm cells. And reactivate all the recessive genes and cause a person to give birth to a Australopithecus type creature. This feels like a dumb question. But I thought it be worth asking. 2. Are there any combinations of dogs which can not geneticlysp cross breed. I don't mean stuff like it not being practical like a great dane and toy poodle. I mean geneticly unable to breed. 3. And last but not least does evolution have anything to do with the disorder of Down's syndrome. and Does Down's syndrome appear anywhere else in the animal kingdom besides humans. Thanks to anyone who can answer these.

07-31-2002, 07:32 AM	#4
Oolon Colluphid Contributor Join Date: Sep 2000 Location: Alibi: ego ipse hinc extermino Posts: 12,591	Ref the dogs, I�ve not heard of anything except the physical practicalities of great danes x chihuahuas etc. But that could be enough. There�s two things to bear in mind. 1) Closely related species (as sufficiently diverse dogs would be) can and do interbreed. Mallards and pintails, lions and tigers, llamas, camels and vicunas, and a range of butterflies (I�ll check which if you like) spring to mind; Mr Darwin can doubtless suggest plant species. And there�s ring species such as Ensatina salamanders and Larus gulls, which interbreed all round the geographical ring, till it meets, where they don�t. Whether or not the offspring are fertile is almost beside the point, and brings me to... 2) Morphological difference (eg here, size of genitalia) is just one of a host of reproductive barriers between species. If we go (for simplicity) with the Biological Species Concept, then a species is simply a bunch of organisms that can interbreed among themselves, but not with anything else. Speciation is therefore the evolution of reproductive barriers, of isolating mechanisms. There�s barriers both before and after mating. Pre-mating ones include variations in courtship rituals, scents and calls, size or shape of genitals, and timing of reproductive cycles. Post-mating ones are things like hybrid inviability (embryo doesn�t develop properly), or hybrids (and remember, we�re all hybrids -- of our parents� genes) which develop to healthy adulthood, but which may have any degree of infertility, such as horse x donkey making sterile mules and hinnies. So we find in nature a full range of situations, from fully interbreeding, to don�t �want� to interbreed but could, to production of healthy but sterile offspring, to don�t interbreed and nothing comes of it even if they do. And several of the steps have been observed to evolve (by �microevolution�, of course ). Being genetically incompatible, which Tim asks about, is almost irrelevant: mere courtship rituals keep mallards and pintails separate in the wild, but fertile offspring can be produced in zoos. Northern and southern leopard frogs happily interbreed, but the embryo fails to develop correctly, and it seems it�s just a case of each half of the genetic recipe requiring different 'cooking' temperatures. That�s a genetic incompatibility, but it�s based on only a small difference, and an environmental not a genetic one at that. Speciation is all a matter of degree of isolation -- which is what evolution predicts -- and isolation can take many forms. So with dogs, my humble layman�s opinion is that big and little dogs are potentially separate species. There�s both pre- and post-mating barriers (genitals don�t fit, and the severe difficulties of birthing pups from a big male dog / little female dog cross. If medium-sized dogs were wiped out, they would de facto be separate species. But since there can be gene flow via the medium-sized dogs, I guess they�re still one species. It�s more like the ring species situation, with it unclear whether they�re one species or two. Hope that helps. Cheers, Oolon [ July 31, 2002: Message edited by: Oolon Colluphid ]</p>

07-31-2002, 09:26 AM	#9
Late_Cretaceous Veteran Member Join Date: Oct 2001 Location: Alberta Posts: 1,049	" except the physical practicalities of great danes x chihuahuas etc" It sure does not stop them from trying. I once saw a tiny male dog (breed=?) trying desperatly to mate with a large female German Shepard. She was actually trying hard to accomodate him, but try as he might he just could not mount her. Finally, he gave up in frustration, lay on his side and blew his load. SO, I think you are correct to say that size is a reproductive barrier that could potentially get bigger with generations until they become separate species. I suppose this could happen if a population of island dwarfs of some animal were reintorduced to the mainland. [ July 31, 2002: Message edited by: Late_Cretaceous ]</p>

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07-31-2002, 06:41 AM	#3
nogods4me Contributor Join Date: Jun 2001 Location: Baltimore, MD USA Posts: 17,432	a variation on the original question might be: Is it possible to reactivate, or repair the gene we have that used to produce vitamin C? Could we give injections to expectant mothers that would be able to restore funcionality to that gene? no more scurvy.

07-31-2002, 08:36 AM	#6
Dr Rick Veteran Member Join Date: Jul 2000 Location: USA Posts: 5,393	All domestic dogs, wolves, coyotes, and jackals can mate with each others (barring size constraints) to produce viable and fertile offspring, but not with foxes because foxes have different numbers of chromosomes than the others. Rick

07-31-2002, 08:53 AM	#8
hyzer Veteran Member Join Date: Jan 2001 Location: philadelphia Posts: 1,844	“Would it be possible to alter an embryo's genes or an egg or sperm cells? And reactivate all the recessive genes and cause a person to give birth to a Australopithecus type creature.” I once posted (on II if I remember correctly) that this very scenario would make a great work of fiction (ala Jurassic Park) – scientist discovers DNA altering breeding method by each new generation is actually a step backwards into the evolutionary history of that species, scientist breeds proto-bacteria, then proto-mice, perfects the method in which each step is bigger and bigger, further into the past, goes mad when the human experiments succeed . . . (but fundamentalists protest that the resulting creatures “don’t prove evolution” ).

07-31-2002, 09:31 AM	#10
Late_Cretaceous Veteran Member Join Date: Oct 2001 Location: Alberta Posts: 1,049	WOuld mitochondria from distantly related species work in each other's cells? If you could kill the mitochondira in all the cells of a human, then replace them with mitochondira from a shark, would it work (assuming the technology to do it worked of course)?

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