Why do some eggs contain two yolks? What causes double yolks?

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Offline chris

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I was asked today by someone why some eggs are "double yolkers"; embryologically, I suspect that the gene programme that drives the development of the egg tissues plays out in two tissues side by side; these tissues are derived from some founder tissue that, rather like a monozygotic twin, spilts up earlier in the developmental pathway.

But I'd be interested in the insights and wisdom - and accurate answers - of others.

Chris
I never forget a face, but in your case I'll make an exception - Groucho Marx

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Offline CliffordK

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The egg is essentially a single cell.

I was thinking it was like monozygotic twins.  However, I believe the differentiation of the yolks comes prior to fertilization.  Whereas in mammals, at least for monozygotic twins, the separation comes after fertilization.

I would be curious about a comparison of the genetic material between the yolks.

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Offline chris

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The yolks are just a fat-rich energy store. The eggs we eat are unfertilised, as a rule, so the genetics argument ought not come into it - both yolk structures and related tissues should be genetically identical, I would think.

chris
I never forget a face, but in your case I'll make an exception - Groucho Marx

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Offline RD

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« Last Edit: 22/01/2012 22:11:14 by RD »

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Offline CliffordK

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It seems it's dizygotic twins ...
http://www.poultry.allotment.org.uk/Chicken_a/Chicken_Egg_Excess/double-yolk-eggs.ph
That would make a lot of sense.
After meiosis, one would end up with haploid cells, which would be unlikely to divide again until fertilization. 

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Offline chris

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Thank you; that's very helpful. A double ovulation.
I never forget a face, but in your case I'll make an exception - Groucho Marx