Chromosomal Pet Peeve

[Bert Gold]

Colleagues

I continue to study very hard for the Genetics Boards exam and find
that I have again stumbled on the difficult issue of how many chomosomes
(and how much DNA) is present when during meiosis.

This is a favorite question of the exam-gods, but I always seem to
over interpret (probably from doing a Ph.D. in spermatogenesis).

At any rate, the issue I would like your help with is this:

How can all the textbooks continue to maintain that the number of
chromosomes during MI of Meiosis and M2 of Meiosis (until completion)
always remains at 2N?  At this point they mostly admit that the
amount of DNA goes up to 4C before leptotene, but how can you
have 4C,2N?  Apparently, the textbook makers think that one tetrad equals
one chromosome?  At any rate, are they really counting centromeres
when they say chromosomes??

If you can't figure out what the hell I'm writing about, you are
welcome to look at Vogel and Motulsky, page 36, or just try to
answer the problems in Thompson and Thompson, page 30, problems
4a and 4b (I think the answers at the end of the book are wrong;
but your opinion is welcomed).

Bert Gold, Ph.D.
UCSF