= Double fertilization
{wiki}
In the common <angiosperm> arrangement, one <sperm> fuses with the <ovum> to form a <diploid> <zygote>; another fuses with the central <biological cell>'s two polar <cell nuclei>, initiating <endosperm> with three <chromosome> sets. The <zygote> develops into a <plant embryo>, and the <ovule> develops into a <seed>.<Biology 2e by Mary Ann Clark and others/32.2 Pollination and Fertilization>[Biology 2e, §32.2 Double Fertilization, Figure 32.18]{ref}
For an original counting example, stipulate a <plant> with $2n=14$ <chromosomes> and the common two-polar-nucleus arrangement. Each <haploid> <sperm> and <ovum> contributes $n=7$. The <zygote> therefore has $7+7=14$ <chromosomes>, while the initiating <endosperm> <cell nucleus> has $7+7+7=21$. The maternal <seed coat> remains derived from $2n=14$ <plant tissue>; the whole <seed> has no single uniform <chromosome> count. This is bookkeeping for a stipulated example, not identification of a particular <species>. It follows by counting the <chromosome> sets entering each fusion, rather than assigning one count to everything enclosed by a <seed coat>.
Back to article page
