More Life Cycles

This is an extension of the Playing Card Meiosis module.

If you’ve got a multicellular stage in there, just remember that the cells are dividing with mitosis.  This gives us a variety of life cycles:

The “Animal” life cycle (diplontic) – the major body plan is diploid.

The "diplontic" life cycle is also known as the “gametic” cycle.  From Menchi http://upload.wikimedia.org/wikipedia/commons/2/23/Gametic_meiosis.png

The “Fungal / Protist” life cycle (haplontic) – the major body plan is haploid.

The "haplontic" life cycle is also known as the “zygotic” cycle.  From Menchi http://upload.wikimedia.org/wikipedia/commons/7/7f/Zygotic_meiosis.png

The “Plant” life cycle (haplodiplontic) – the major body plan alternates haploid and diploid.

The "alternation of generations” or
the “sporic” cycle.  From Menchi http://upload.wikimedia.org/wikipedia/commons/8/86/Sporic_meiosis.png

Note that these are not comprehensive!  Part of the reason for life’s diversity is that nature has supported many different ways to address the same survival challenges.  Having a multicellular haploid stage can be viewed as a chance to weed out “bad alleles”:  it’s only in diploid organisms that dominant and recessive traits have meaning.  Diploid organisms, like human beings, can and do mask lethal or unhealthy alleles.  This is what happens when two healthy parents give birth to a child with Tay Sach’s disease or cystic fibrosis.

If you want to see a cool “solution” based on life cycles, check out the Hymenopertera! Sex is not determined by an X or Y chromosome.  Instead, females are diploid and males are haploid!

MISCONCEPTION: ONLY DIPLOID CELLS DIVIDE BY MITOSIS.Corrected Statement: All eukaryotic cells are potentially capable of mitotic division.
Explanation: Many students try to group things based on simple characteristics. Being diploid or haploid doesn’t affect the necessity for cell division. Since most biology books communicate human cell features, one might think that haploid cells don’t divide through mitosis—and they don’t, in humans! But there are many organisms that are multicellular haploids—bee drones (males), for example, are haploid. They form by mitotic divisions of an unfertilized ovum from the queen bee. The males also form sperm, of course—but since they’re already haploid, the sperm are not formed through meiosis in the male! (From Science³; Rawle et al. 2014)