The aura can be in the form of prismatic colors, flashes of light, and sometimes stars. They usually last about 20 minutes and then go away. If these flashes or lines of light occur without a headache, it is called an ophthalmic migraine, or a migraine without a headache.
In gymnosperms and flowering plants, the megaspore is produced inside the nucellus of the ovule. During megasporogenesis, a diploid precursor cell, the megasporocyte or megaspore mother cell, undergoes meiosis to produce initially four haploid cells (the megaspores).
meiotic recombination; mitotic recombination; MEIOSIS is essential to maintaining the proper complement of chromosomes in sexually reproducing organisms. By following one round of DNA replication with two rounds of cellular division, meiosis effectively halves the chromosome content of participating cells. Prior to the first meiotic division, homologous chromosomes pair and, in many organisms, undergo recombination. Both crossovers, characterized by the reciprocal exchange of flanking markers, and noncrossovers, in which flanking DNA remains unchanged, result from these recombination events.