[Chlamydomonas] need help for cross experiment

Elizabeth Harris chlamy at duke.edu
Sat Dec 17 08:17:53 EST 2005


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 
mitotic division.

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

Chlamydomonas Center
http://www.chlamy.org/



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