Loss of Egg Yolk Genes in Mammals and the Origin of Lactation and Placentation
Author Information
Author(s): Brawand David, Wahli Walter, Kaessmann Henrik
Primary Institution: Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland
Hypothesis
The emergence of lactation and placentation in mammals allowed for the gradual loss of yolk-dependent nourishment during mammalian evolution.
Conclusion
The study shows that the loss of egg yolk genes in mammals is linked to the evolution of lactation and placentation.
Supporting Evidence
- The three ancestral vitellogenin-encoding genes were progressively lost during mammalian evolution.
- Major milk resource genes, caseins, appeared in the common mammalian ancestor ∼200–310 million years ago.
- Monotremes retained a functional vitellogenin gene, consistent with their intermediate reproductive state.
Takeaway
Mammals used to rely on egg yolk for baby nourishment, but over time, they developed milk and placentas, which made the yolk less important.
Methodology
Comparative genomics analyses and evolutionary simulations were used to study the loss of vitellogenin-encoding genes in mammals.
Limitations
The study's estimates of inactivation times are approximate due to uncertainties in the simulation-based dating approach.
Statistical Information
P-Value
p<0.05
Confidence Interval
95% prediction interval of ∼110–240 Mya for VIT3 inactivation
Statistical Significance
p<0.05
Digital Object Identifier (DOI)
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