Liming Luo wrote:
>Now I'm doing Chlamydomonas tetrad analysis. I meet some problems
>which really confuse me. Sometimes my zygotes produce 8 progeny,
>sometimes 4. The weird thing is that in some cases, I get 5 progeny
>from 1 zygote, 3 big and 2 small. It looks like one progeny's
>already divided into 2. Sometimes I get more than 8 progeny from 1
>zygote. I don't know how to explain these phenomena.
>Has anybody met such things before?
Sometimes getting 4 progeny and sometimes 8 is normal, and seems to
depend on the strains involved, the temperature and light
intensity, and the age of the zygotes - zygospores that have been
stored for a couple of weeks usually give a higher proportion of 4's
rather than 8's.
See VanWinkle-Swift (1977) Journal of Phycology 13, 225-231, and The
Chlamydomonas Sourcebook page 167.
I think Forster et al. (1980) Current Genetics 1, 137-153 also
comment on this phenomenon. In their experiments conditions were
selected that produced predominantly 8 progeny, so that the
segregation of chloroplast genes could be followed through the first
Getting 5 progeny rather than 4 is not so common in my experience,
but I think your explanation is correct, that one of them has already
divided again before the zygospore wall is ruptured. If you let all
five progeny grow up, do the two smaller ones form colonies with
identical genotypes? If so, then just ignore one of these and score
the tetrad as if it consisted of four unique cells.
Elizabeth H. Harris