Ploidy and the evolution of endosperm of flowering plants.

In angiosperms, spermatozoa go by pair in each pollen grain and fertilize, in addition to the egg cell, one of its sister cells, called the central cell. This "double fertilization" leads to the embryo on the one hand and to its nutritive tissue, the endosperm, on the other hand. In addition, in most flowering plants, the endosperm is triploid because of a doubled maternal genetic contribution in the central cell. Most of the hypotheses trying to explain these eccentricities rest on the assumption of a male/female conflict over seed resource allocation. We investigate an alternative hypothesis on the basis of the masking of deleterious alleles. Using analytical methods, we show that a doubled maternal contribution and double fertilization tend to be favored in a wide range of conditions when deleterious mutations alter the function of the endosperm. Furthermore, we show that these conditions vary depending on whether these traits are under male or female control, which allows us to describe a new type of male/female conflict.