Double-fertilization

Strickberger, M.W. 1968. Genetics. The Macmillan Company. New York, pgs. 42-43.

In higher plants, such as corn, the pollen grain contains one tube nucleus and two generative nuclei. The female embryo sac contains a gametic nucleus, which is haploid (n), and a diploid endosperm nucleus (2n). The fertilization process begins when the pollen grain lands on the stigma and germinates into a long pollen tube. The pollen tube contains two male sperm nuclei (n). Double fertilization occurs when one sperm nuclei fertilizes the haploid embryo nucleus and the second sperm nuclei fertilizes the diploid endosperm nucleus. The result is diploid (2n) embryo tissue and triploid (3n) endosperm tissue in the developing seed.

Expression of the alleles contributed by the male parent on the endosperm tissue is referred to as xenia.

Meiosis leads to 4 haploid microspores in the male and four macrospore mother cells in the female tissue. Each of the 4 haploid microspores develops into a pollen grain. Only one of the four haploid megaspore cells becomes the functional female gametocyte. The functional megaspore cell divides mitotically three times to form eight haploid nuclei.