Loss of egg yolk genes in mammals and the origin of lactation and placentation

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The emergence of alternative nourishment resources (lactation and placentation) during mammalian evolution set the stage for mammals progressive loss of egg yolk nourishment (as a consequence of the loss of egg yolk genes). Credit: Image: Rasmus Kaes ...
The emergence of alternative nourishment resources (lactation and placentation) during mammalian evolution set the stage for mammals' progressive loss of egg yolk nourishment (as a consequence of the loss of egg yolk genes). Credit: Image: Rasmus Kaessmann

If you are reading this, you did not start your life by hatching from an egg. This is one of the many traits that you share with our mammalian relatives. A new paper in this week’s PLoS Biology explores the genetic changes that led mammals to feed their young via the placenta and with milk, rather then via the egg, and finds that these changes occurred fairly gradually in our evolutionary history. The paper shows that milk-protein genes arose in a common ancestor of all existing mammalian lineages and preceded the loss of the genes that encoded egg proteins.


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