Formation of chromosomes in endosperm of a plant
This process involves fertilization in plants. When a megaspore mother cell with 26 chromosomes undergoes meiosis, it produces four haploid cells, one of which becomes the egg cell. Meanwhile, a pollen grain with half the chromosome number (13 chromosomes) fertilizes the egg cell, resulting in a diploid zygote with 39 chromosomes. Later, the zygote undergoes mitosis to form a structure called the endosperm, which nourishes the developing plant embryo. This endosperm maintains the diploid chromosome number (39) because it comes from the fusion of a haploid egg cell and a haploid pollen grain during fertilization.