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I'm not trying to understand the underlying molecular processes, rather understand it conceptually. This is what it says in my coursebook:

"The imprint, obtained during gametogenesis, is reversible: an allele with paternal imprint will, after transmission through the female germline, be changed into an allele with maternal imprint.

In other words:
Paternal imprinting means that some gene obtained from your father is 'silenced'. These 'silenced tags' remain during your whole life, but are reset during the formation of egg-cells or sperm-cells.
Some genes are always silenced in egg-cells, others in sperm-cells.

There is a continuous activation and deactivation in function of the parent who transmits the gene"

I don't understand how the first paragraph and the last paragraph can both be correct.

If the paternal imprint changes into a maternal imprint after passing through the germline, this implies that the gene is just deactivated in the chromosome that is passed on and we call is paternal or maternal depending on who passes it on.

On the other hand, the last paragraph (and the middle one) imply that, if you receive a gene with maternal imprint from your mother as a man, your body resets the 'silencing' during gametogenesis, realizes a sperm cell is being made and decides not to silence it since it will now be passed on from a father. Only this can explain why it would lead to continuous activation/deactivation or reversibility.

Which of the two is correct?

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Only during the formation of egg-cells or sperm-cells one can leave the maternal or paternal imprint, respectively. So for example a man, will leave its paternal imprint on an allele (during spermatogenesis) that was given by his mother (while the allele was maternally imprinted in the rest of his body).

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  • $\begingroup$ I understand that, but the first line implies constant switching between paternal and maternal imprinting, which implies that the allele is constantly deactivated, since it's always imprinted and that's the definition of imprinting. The last line says there's constant activation/deactivation of the allele, how can this be true if there is a constantly switching imprint as opposed to imprint/no imprint? $\endgroup$ – Joshua Sep 1 '17 at 13:34
  • $\begingroup$ Sorry but I don't understand the confusion. The first sentence is the same as I try to explain. The imprinting changes only during gametogenesis, in other words during sperm or egg formation. Only then the imprint is changed (to paternal or maternal respectively). This is what they mean with reversible. I don't see that it implies constant switching. What word does imply this?? $\endgroup$ – user35628 Sep 1 '17 at 13:54
  • $\begingroup$ "There is a continuous activation and deactivation in function of the parent who transmits the gene" $\endgroup$ – Joshua Sep 1 '17 at 19:29
  • $\begingroup$ Yeah in either father's or mother's gametogenesis, respectively, the allele will be activated or inactivated. Maybe a real life example will help you understand how it works, Prader-Willi and Angelman syndrome... $\endgroup$ – user35628 Sep 1 '17 at 20:54
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    $\begingroup$ I think I understand it now, the gene that's being deactivated isn't the same for paternal imprinting and maternal imprinting. This wasn't explicitly mentioned in the course so I didn't think to make a distinction. Now it makes sense that the imprint of 1 gene disappears so it becomes active, while the imprint of the other appears and it becomes inactive. Which also explains activation/deactivation together with a switching of imprint. Thank you! $\endgroup$ – Joshua Sep 2 '17 at 13:57

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