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Slide 1

On eggs and milk

Human beings feed their newborn on maternal milk. Crocodiles lay eggs in which their progeny find everything they need to develop. And platypuses do a bit of both by laying eggs and then offering milk to their offspring. How did the passage from egg-laying to lactation happen? And when? Actually…did animals go from egg-laying to maternal milk? Or from milk to eggs? How do you rummage around a species’ past to find out? So many questions, to which the answers are hidden…in our genes.

tell me a story, gene

To understand how the processes of lactation and laying eggs began, you have to choose genes that are essential to both. Maternal milk contains a protein known as casein, in huge quantities. Consequently, the casein gene will be found in species that produce maternal milk. Eggs, on the other hand, are full of a protein known as vitellogenin. The vitellogenin gene can be found in species that lay eggs. On choosing to study the genes of these two proteins, researchers can compare their fates and, in so doing, try and understand what happened to them over time.

Slide 2

a gene’s fate

If a gene is useful to a species, then it will undergo very little change over time because it has to preserve its function. A gene which is less essential for the survival of a species, however, can accumulate modifications until – in the most extreme example – it becomes useless and dies, so to speak. So, studying the state of both the casein and vitellogenin genes in different species will tell us how events occurred over time, and in which species.

Slide 3

reading a gene

One whole aspect of bioinformatics focuses on understanding a gene’s past. Researchers have compared the casein and vitellogenin genes in different species. And this is what they discovered:

  • the casein gene first appeared about 300 million years ago in the ancestor of mammals,
  • at the same time, the vitellogenin gene was progressively lost in mammals.
Slide 4