posted
I googled a bit and found this article about Flora. Apparently the babies' DNAs aren't exact copies of hers, but I don't really understand how they wouldn't be. I skimmed through the Wikipedia article on this phenomenon, but I don't think I have a sufficient background in genetics to get it. Maybe someone else here who's more biology-minded than me could explain?
Posts: 952 | Registered: Jun 2005
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posted
Going off what little I recall about parthenogenesis and this paragraph from the wikiarticle:
quote:Parthenogenesis is distinct from artificial animal cloning, a process where the new organism is identical to the cell donor. Parthenogenesis is truly a reproductive process which creates a new individual or individuals from the naturally varied genetic material contained in the eggs of the mother. A litter of animals resulting from parthenogenesis may contain all genetically unique siblings without any twins or multiple numbers from the same genetic material. Parthenogenic offspring of a parthenogen are, however, all genetically identical to each other and to the mother, as a parthenogen is homozygous.
my understanding is that each parthenogenic offspring of the original non-parthenogenically produced mother only gets one copy of each chromosome, just like a normal offspring would. However, where a normal offspring would get a second set of chromosomes from the father, the parthenogenic offspring gets a duplicate set of the ones they got from Mom.
An example, pretending that there were only 3 pairs of chromosomes (two autosomal pairs, and one sex chromosome pair).
Original female: A1 B1 X A2 B2 X Parthenogenic offspring: A1 B1 X A1 B1 X
OR
A2 B2 X A2 B2 X
OR
A1 B2 X A1 B2 X
OR
A2 B1 X A2 B1 X
Did that clarify things at all?
Posts: 32919 | Registered: Mar 2003
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posted
I concur. I read a fascinating book on parthenogenesis when I was in Jr. HS (okay, I was a geek, and genetics was my strong suit.)
Posts: 21182 | Registered: Sep 2004
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posted
Let me add that "crossing over" a process that occurs 2-3 times per chromosome in Human beings, adds a great deal of genetic variability. The process happens during Prophase I of Meisosis, and it is a common misnomer that the formation of chiasmata occurs *only* after the homologous cromosome synapse. In reality, the first chiasmata forms even before the formation of the synaptonemal complex.
The "crossing over" process enhances genetic variablity by passing on genes from one homoluge to another --> a chromosome coding for Blue eyes, for instance, might be changed to code for Brown eyes.
An interesting point is that recombination (the process of crossing over) occurs are greater and greater percentages when the two genes are further apart on the chromosome. In fact, 2 of the Mendelian traits actually do NOT assort independently! They are on the same chromosome, and because of the chances of Recombination, only act as though Independent assortment applies.
Posts: 3060 | Registered: Nov 2003
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But that doesn't explain how the komodo's babies are not genetically identical to her. Is there room for random mutation in parthenogenesis? Or is there another explanation?
Edit: Phanto posted while I was writing mine. So does the crossing-over thing occur in reptiles as well?
Posts: 952 | Registered: Jun 2005
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quote:But that doesn't explain how the komodo's babies are not genetically identical to her.
Point: it does, actually. If you scrambled your genes from one chromosome to the next, divided them in half, replicated them, and then scrambled them randomly again, the resulting organism would not be genetically identical to you. (Not that that's exactly how it works, but just an illustration.) Let's put it in (very much simpler and simplified) plant genetics terms. If you have a red flower gene and a white flower gene (we'll assume red is dominant and RR makes red, Rr makes pink, and rr makes white) and you have Rr genes in a plant, offspring of that plant fertilized by the same plant can be either genotype RR, Rr, or rr. The phenotype can be red, pink, or white. Just assuming that this one plant self-fertilizes, there can be multiple offspring with different appearances. And that's only one gene of millions. The possible variety is almost infinite. It's quite a process.
quote:a chromosome coding for Blue eyes, for instance, might be changed to code for Brown eyes.
Sorry. It's just that eye color examples make me laugh so much; there are so many genes in play and the whole issue is so rife with incomplete dominance. I usually either go to plant genetics, or use something like chin clefts, because eyes are so complicated...
Posts: 21182 | Registered: Sep 2004
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posted
- Right, the eye color examples are flawed. I kinda regret using it now . - Nell Gwyn: Yes, crossing over should occur in any animal.
The independent assortment, that homologues seperate, is a much greater factor ^^. If you have ten pairs of chromosomes, then just by that factor, you can produce:
2^10 = 1024 results.
Factor in crossing over, and, hopefully, sexually mating with an other animal, and you can get a massive amount of possiblities, about 72 trillion in Humans, not accounting for further randomising factors.
Posts: 3060 | Registered: Nov 2003
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posted
Oh, whoops! I just realized I'd misread rivka's post. Okay, I think I understand it now. Thanks, all! Posts: 952 | Registered: Jun 2005
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Sorry. It's just that eye color examples make me laugh so much; there are so many genes in play and the whole issue is so rife with incomplete dominance. I usually either go to plant genetics, or use something like chin clefts, because eyes are so complicated...
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