Egg yolk gene loss was mammals' gain

Mammals lost their egg yolk genes after acquiring genes for milk proteins, according to a linkurl:study;http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0060063/ published yesterday in PLoS Biology. The results pinpoint an important step in how mammals evolved, the authors say. Lactation is "what makes us mammals, basically," said linkurl:Henrik Kaessmann,;http://www.unil.ch/cig/page7858_en.html/ who led the study. "Using egg yolk genes as markers, we foun

Elie Dolgin
Mar 17, 2008
Mammals lost their egg yolk genes after acquiring genes for milk proteins, according to a linkurl:study;http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0060063/ published yesterday in PLoS Biology. The results pinpoint an important step in how mammals evolved, the authors say. Lactation is "what makes us mammals, basically," said linkurl:Henrik Kaessmann,;http://www.unil.ch/cig/page7858_en.html/ who led the study. "Using egg yolk genes as markers, we found a unique way to put a timeframe on how key transitions in mammals occurred." There are three types of mammals: true placental mammals, linkurl:marsupials;http://www.the-scientist.com/news/home/53187/ and monotremes. Though each type nourishes its young in a different way, they all use milk to some extent, and their eggs have far less yolk than their reptilian and bird-like ancestors. But in the evolution of mammals, there's a longstanding "chicken and egg" question, or rather, a milk and egg question: What came first in the mammalian lineage — genes involved in lactation, or the loss of genes...
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