An ascospore is a spore contained in an ascus or that was produced inside an ascus. This kind of spore is specific to fungi classified as ascomycetes (Ascomycota).
Typically, a single ascus will contain eight ascospores. The eight spores are produced by a combination of a meiotic division followed by a mitotic division. The meiosis division turns the original diploid zygote nucleus into four haploid ones. That is, the single original cell from which the whole process begins contains two complete sets of chromosomes. In preparation for meiosis, all the DNA of both sets is duplicated, to make a total of four sets. The nucleus that contains the four sets divides in two stages, separating into four new nuclei – each of which has one complete set of chromosomes. Following this process, each of the four new nuclei duplicates its DNA and undergoes a division by mitosis. As a result, the ascus will contain four pairs of spores.
The Fungi Saccharomyces produces ascospores when grown on V-8 medium, acetate ascospor agar, or Gorodkowa medium. These ascospores are globose and located in asci. Each ascus contains one to four ascospores. The asci do not rupture at maturity. Ascospores are stained with Kinyoun stain and ascospore stain. When stained with Gram stain, ascospores are gram-negative while vegetative cells are gram-positive.
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