Date: Wed, 18 Nov 1998 11:20:36 -0500 From: "Mellard, David" <dam7@cdc.gov> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg3628$foo@default> Subject: genetics
Hi Carl,
>I have 5 or 6 juvenile plants of S. leucophylla 'typical form' x S.
>leucophylla 'anthofree form' it will be some time before they flower,
>however, I expect the same results as crossing any other albino form with a
>pigmented form. Most of the flowers should be an intermediate of sorts with
>some remaining yellow and other remaining the typical red.
I would expect all the plants in such a mating to be normal pitcher color
and normal flower color but then maybe plant genetics are different from
mammalian genetics in this respect. Here's my reasoning which I throw out
for common debate so that we'll learn a bit from those who are versed in
plant genetics.
Anthocyanin production is coded by a series of alleles (genes) that produce
different enzymes responsible for the conversion of simple carbon molecules
into anthocyanin. In the antho-free lecuo, both alleles (two of the same
genes on corresponding chromosomes) are not capable of coding for a specific
enzyme in the anothcyanin pathway and therefore anthocyanin is not produced.
The normal leuco has two alleles (genes) one of which at least is capable
of producing (that is, codes for) the enzyme. The other allele may or may
not be capable of coding for the enzyme in question.
Therein lies the cruz of knowing what you will get when the two plants are
bred together. If the normal leuco is homozygous (for instance, both
alleles are capable of coding for the enzyme), then the offspring from
mating with a antho-free plant will all be normal leuco with anthocyanin and
hence with red pigment. If the normal leuco is heterozygous (one allele is
capable of coding for the enzyme, the other allele is not capable), then the
offspring from mating with an antho-free plant will be a mix of normal and
antho-free plants. If I remember correctly without actually doing gene
matching, 50% will be antho-free. The mix of antho-free leuco and normal
leuco happens because of the division of the two alleles by both plants as
they produce pollen and ovums (if that's what it's called in plants). When
the two are combined back together upon pollination it's now possible to get
(1) plants with both alleles capable of producing the enzyme for anthocyanin
or (2) plants with both alleles not capable of producing the enzyme for
anthocyanin or (3) plants with one of the alleles capable of producing the
enzyme for anthocyanin. If however, the normal leuco is homozygous with
both genes coding for the enzymes, then all off-spring will be heterozygous
and thus be capable of producing anthocyanin.
One thing I haven't figured out in all this is the influence of modifying
factors, that is, other genes that can influence the color of a pitcher or
flower, and whether or not that comes into play when it comes to anthocyanin
production. My impression is that it is a factor because of the varying
degree of anthocyanin production (that is, the variation in the redness of a
plant) in plants.
David
Atlanta
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