The meristem in at least one of the lateral buds of a corn plant develops into an ear. This meristem includes 500-1000 lateral meristems with mother cells with diploid sets of chromosomes, 10 chromosomes from each of that plant’s parents. Meiosis occurs in this diploid cell, resulting in 4 haploid cells, each cell having only a single set of 10 chromosomes consisting of a random mix of the two parent’s chromosomes. Three of the 4 haploid cells degenerate, leaving a single megaspore. This megaspore nucleus undergoes mitosis three times, resulting in 8 cells within the megaspore structure now called the embryo sac. One cell at the bottom of the embryo sac becomes the egg cell while two of the haploid cells fuse in the center of the embryo sac.
The embryo sac (ovule) is enclosed in an ovary, at part of the female part of the parent plant. Part of this female flower is the silk., extending from a single ovary and attached to its ovule. The male flower also produces pollen via meiosis followed by a single mitosis, resulting in two haploid nuclei. A pollen grain adhering to the silk, germinates and extends down the silk to the ovule. Upon entrance of the ovule, one nucleus fuses with the haploid egg cell forming a diploid nucleus to become the seed embryo. The other pollen haploid nucleus fuses with the two ovule nuclei in the center of the ovule resulting in a triploid nucleus, having two sets of chromosomes from the female parent and one from the male. This triploid nucleus undergoes mitosis to become the endosperm of the seed.
Whereas the inheritance of the embryo, and its resulting mature plant, is determined equally by the genetics of the male and female parents, characteristics of the endosperm is slanted towards the genetics of the female parent. If the female parent has the recessive Y1 gene, and thus a white endosperm, but the pollen is from a parent with dominant gene and thus has yellow endosperm pigment, the resulting endosperm will be lemon white in color. The female genetics has the major affect on endosperm function in the maize seed because it contributes two of the three sets of chromosomes in endosperm cells.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.