ed at teosinte.agron.missouri.edu
Thu Oct 29 23:38:30 EST 1998
Thank you for contacting MaizeDB for information about the class' observation.
We received from you 3 notes, which I think were all equal. I'm forwarding
this to the Maize Net, as some others may wish to comment.
First, the white seedling probably will not last long, because the energy
supply from digestion and transport of the starch in the kernel will run out.
If the seedling happens to turn green (which some mutants, called 'virescent',
turning green, do), it might begin to carry on photosynthesis and survive. If
you put into a small vial a sugar solution, cut a leaf and insert it in the
solution, the sugar can help maintain the energy required, and plants have
actually been carried to shaky maturity that way. Reproducing the present
seedling is probably too much to hope. Without a series of seedlings, a
controlled experiment cannot be conducted on feeding. Class materials
segregating for white seedlings can be obtained from various sources.
Second, the cause is most likely a recessive mutation, as you have suggested.
Nuclear genes that control chlorophyll production, or other associated
constituents, or assembly of the molecules in the chloroplast, or stability of
the chloroplast, are known (well over 100 could be distinguished so far in
genetic studies). So any one of these could be present in the popcorn source,
carried along as a rare or not-so-rare recessive, and by chance two gametes of
the recessive genotype get together. This is a "population genetics" lesson -
variations occur in nature, and affect traits according to genotypic results.
Repetition of the 600-seed experiment might turn up another, or not, and it
might be the same mutation, or not (a lesson in sampling and in diversity -
but will the information gained be firm?). The recessive, pre-existing in the
population, might also be joined by a new mutation of the same gene and give a
recessive zygote. An alternative cause, much less likely, is a mutation in
the genetic material of the chloroplast itself. There are a few such examples
known, but their occurrence is rare.
I hope this is helpful; good luck with teaching the experimental method.
Possible causes, and reasoning how additional experiments vs. new experiments
may distinguish them....
Geneticist, Agric. Res. Service, U.S. Dept. of Agric., and Prof., Univ. of
tcasal at earthlink.net wrote:
> message originates from 188.8.131.52 909642347
> Submittor's Name: Teresa Casal
> Submittor's Email Address: tcasal at earthlink.net
> Comments Follow:
> I am a science middle school teacher in Miami Florida in search of
>information about an unusual situation with one of our plants. I gave my
>sixth grade students some popcorn seeds to germinate and plant while
>teaching a unit on the scientific method. One of the plants out of a lot
>of approximately 600 popcorn seeds which we have planted has us totally
>baffled. The stalk and the leaves of the seven day seedling are completely
>white.Although I imagine that this is some form of recessive trait, I must
>admit that I am not knowledgable about the possible traits of popcorn
>seedlings. I would like to obtain some information so we can benefit from
>this learning experience. I do not have Internet services in my classroom
>this year, but I have promised my bilingual students that I would ask a
>scientist for them, in order to learn more about what has ocurred with
>this plant, how rare is this occurrence and to gather ideas in how we
>could grow the plant outside. We are wondering if this
> characteristic could be reproduced and how this would be done. Currently
>it is inside a 35 mm film canister in my classroom window. Thank you for
>all the help that you can give us. If you wish to e-mail some web sites or
>information my address is included in this message. My address at school
>is: Teresa Casal (Science teacher)
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> Remote IP address: 184.108.40.206
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