This gene gives instructions for making a yolk protein that gets chopped up by enzymes in the last stage of egg development, inside a teleost's ovary.

ECONOMIST: Fish genetics

But other contributing factors to their include coastal development, egg poaching, ocean pollution and global warming.

CNN: Turtles in race to beat extinction

The theory is that the protein in sperm which triggers chemical changes in the egg, leading to embryo development, is defective or missing from the sperm of some infertile men.

BBC: Sea squirts aid fertility research

Since the 19th century, biologists have been fascinated by the relationship between ontogeny (the development of an adult from a fertilised egg) and evolution.

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That furnishes the egg with enough water to carry out the reactions of embryo development.

ECONOMIST: Fish genetics