Meiosis

Where does meiosis occur? 

• In plants, meiosis occurs in specialized reproductive structures called sporangia, which create spores (= sporogenesis)

  • In seed plants, the male sporangia (microsporangia) are called pollen sacs. The pollen sacs create pollen, also called microspores, which each contain a male gametophyte (known as the pollen tube)

  • The female sporangia are more complicated. Inside each ovule, there is a female sporangium (megasporangium) called the nucellus. The nucellus creates megaspores, which each contain a female gametophyte

• In animals, meiosis occurs in the gonads to create sperm or eggs.

• N.B. Please note that meiosis creates spores in plants (sporic meiosis), but meiosis creates gametes in animals (gametic meiosis). In plants, gametes are created by mitosis.

Ploidy

• The number of sets of chromosomes in a cell

Haploid

• A cell with a single set of chromosomes

• e.g., gametes, spores, cells of a leafy moss

Diploid

• A cell having two sets of chromosomes, one from the biological mother & one from the biological father

• e.g., skin cells of a human; leaf cells of an oak; a zygote