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Re: sex ratios
Hello,
For a 8-grade science project <Sam> did a remarkably good job and, at
least in my opinion, should have placed. (But, on the other hand, one
does not know what the other kids did to place higher!)
Sex ratios, like the weather, are much talked about, but I have not read
either an explanation of the causes, nor a way to control it. While the
type of experiments done by Sam are interesting and somewhat useful,
they do not ask a cardinal question (or at least I am not aware of an
answer to it):
Are killie eggs *differentiated* as to gender at the time they are laid,
i.e. do they show a different chromosomal picture in "male and female
eggs", corresponding to the X- and Y-chromosomes in mammals?
If "yes", then incubating or raising the fry under different conditions
(pH, salinity, temperature, etc) can only enhance the survival of one
gender over the other, NOT "create" it.
If the answer is "no" -- all eggs are identical in that respect -- then
we should continue the quest WHEN do they differentiate and how is it
accomplished/influenced.
I realize, that one most probably can not answer this question in a high
school science project, but how about in a MS thesis or a PhD
dissertation?
In any case, Sam should receive a deserved "WELL DONE!"
Best,
George S
>At the beginning of the year, I did my grade 8 science project on the
>affect of pH on the sex of N. foerschi. I hatched a batch of about 40
>fry in normal tap water (approx. pH: 7.2, total hardness: 90 ppm).
>After a week, I separated half the fishes into water w/ a pH of 6.4 nd
>the other half into water w/ a pH of 8.4. (used sodium phosphate to
>lower pH and baking soda to raise it). The water in the lower pH tank
>had pH: 6.4, total hardness: 90 ppm. The water in the higher pH tank
>had pH: 8.4, total hardness: 90 ppm. I tested the water in the tanks
>every 4 days, and tried to keep the chemistry in the tanks from changing
>throughout the experiment. I "controlled" as many variables as I could
>think of, and everything I did to one tank of fishes was done to the
>other. After about 8 weeks, I counted 1 male : 19 females in the tank
>w/ the 8.4 pH. In the 6.4 pH tank, I counted 5 males : 14 females. If
>you take the results at face value, it means that the 8.4 pH produced a
>sex ratio of 1 male to 19 females, and the 6.4 pH produced a sex ratio
>of 1 male to about 3 females. Incidently, the males raised in the 6.4
>pH showed better colouring and more vigour. Just wanted to tell my
>experiences w/ the whole sex ratio thing.
>
>Anyways, hopefully the thing gets through. You know, first time posting
>and everything. BTW: I missed 3rd place at the science fair by .5%, nuts.
>
>Sam
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