Re: genetics model for meiosis

Normally, this question would fall under the "homework" catergory, but I think it offers a great opportunity to explain some basic concepts in genetics, so I wanted to answer it. Actually, you really only need one deck, if you divide the deck into the major suits (hearts and spades) and minor suits(clubs and diamonds). First, let's go through the basics. Cells grow and divide through the Cell Cycle which consists of a growth phase (G1), followed by a DNA synthesis phase (S), in which the chromosomes are replicated, followed by another growth phase (G2), and ending in cell division through mitosis (M). Gametes (sperm and eggs) are produced in much the same way: however, they undergo meiosis instead of mitosis during M-phase. Most somatic (body) cells are defined as diploid (2N) because they contain two versions of each chromosome - one from each parent. Gametes have half as many chromosomes (N) so they are defined as haploid.

Now for the cards: let's separate out the major suits (hearts and spades), and define this half of the deck as a single diploid genome, in which the card's suit determines its parental lineage, e.g. hearts are maternal and spades are paternal. Thus, 2N = 26 cards (chromosomes) and N = 13 cards (all one suit). This half of the deck represents the genome of a cell in G1, as well that of a cell that has exited the cell cycle to G0. As the cell goes through S-phase, the genome is copied, so we'll use the minor suits as the copies, i.e. the diamonds are copies of the hearts and the clubs are copies of the spades. This gives us 52 cards, or 4N: the chromosome complement of a normal cell in G2.

Mitosis: Simply separate the deck into two piles, such that each pile gets one red card and one black card for each face value. This returns the card number of each daughter pile to 26 (2N). It doesn't matter that some cards are majors and some are minors, since the minor cards are exact copies of the majors. Since the cell can't distinguish between the two copies of each chromosome, it can't segregate them into originals versus copies during mitosis. If you wanted to be more elaborate, you could paperclip the minor suit cards to their corresponding major suit cards (e.g. put the 4 of diamonds with the 4 of hearts, and the King of clubs with the King of spades) as part of replication, just as the cell does with its chromosomes. Then for mitosis, you line up the paperclipped pairs and then pull them apart, placing each card from the pair into one of the two daughter piles (this, again, is how the cell does it). Either way, you should end up with two 2N half decks each with a full complement of cards, i.e. one red and one black card for each face value.

Meiosis: Meiosis is actually divided into two rounds of division: Meiosis I and Meiosis II. To start the process, let's use the paperclipped pairs from the mitosis variation described above. Now for Meiosis I, simply shuffle the paperclipped pairs and deal them into two pile such that each pile gets only one pair per face value, e.g. the red Queens and the black Queens go into different piles. One key to Meiosis I is that it is random, so that each pile should be a mix of red and black pairs. For Meiosis II, just perform mitosis (as above) on each pile, i.e. pull apart the paperclipped pairs and place each in a separate pile. This should give you 4 piles, each with 13 cards (N), or a haploid genome. It is worth noting that each of these haploid piles should contain cards from all four suits, and thus be different from each of the other three piles: this is particularly true if there has been sufficient mutation or recombination prior to meiosis to make the synthesized chromosomes slightly different from the template chromosomes, i.e. if the 2 of diamonds is not quite the same as the 2 of hearts. Thus each gamete gets half of the genome, but it's always a different half.

Now that we've got the deck divided into 4 piles of 13 cards each, who's up for bridge?