Re: HYB:Pink:out crosses

Linda prompts me to make comments on this thread--a good one, I might add.

First, "pink" is 1) white, or better, "non-blue."  Then 2) it is a yellow
with a difference.  The yellow pigment is expressed as Lycopene, not
alpha-Carotene.

Just which yellow carotenes can appear as Lycopene (producing pink) is
uncertain.  The most common carotenes in bearded irises are alpha- and
beta-Carotene.  Some current published material on carotenoid pigments
suggest that Lycopene is converted to alpha-Carotene by an enzyme affecting
both ends of the molecule, and beta-Carotene results when one end of the
Lycopene molecule is twisted around by the same enzyme involved in forming
alpha-Carotene, the other end a result of the action of a different, but
similar, enzyme.

That says, I think, that pink is not simple.  Pink occurs *before* yellow in
the typical sequence of pigment formation if this research applies to
bearded iris color.  Chuck Chapman has commented before, when this was
discussed, that there is other research that suggests there is an alternate
chemical pathway than the one I'm describing which complicates the matter.

To summarize--pink is yellow that failed to be formed.  The pigment *looks*
pink only when no violet or blue shows.  It is simpler to evaluate a cross
if we forget about "pink" and speak only of tangerine beard color showing,
which occurs whatever else is going on.

Tangerine expressed X non-tangerine will give anywhere from zero to half the
seedlings with tangerine beards depending on the genetic makeup of the other
parent, provided the tetraploid genetics follow the simple ratios, which
often they do not.

If the non-tangerine parent has a Tttt makeup, or in other words, have only
one dose of the normal yellow-conversion enzyme, half the seedlings will be
tttt--red bearded condition, the other half Tttt with yellow beards.

If the non-T (tangerine) parent is TTtt, one out of six of the seedlings
will have tttt tangerine beards, the other 5/6ths will have yellow.

If the non-tangerine parent is TTTt or TTTT, zero tangerine-beardeds will
appear in the first generation in the simple genetic sorting.  See the
possible exception below.

If two non-tangerine parents are crossed, both being Tttt, one in four of
the seedlings will be tangerine bearded, the rest yellow.

If two parents with TTtt makeup are crossed, one in 36 of the seedlings will
have tttt makeup, (I think--).

HOWEVER, tangerine beards may not be inherited in as simple a fashion as
this.

Melba Hamblen expressed the well-informed opinion that Purissima, a non-t
white, was one of the parents of Dr. Loomis' SQ-72, Pikes Peak Pink.
Purissima is not known to give tangerine bearded offspring, and may have the
makeup of TTTt.  Tetraploid genetics can produce some very odd results in
extreme cases, making possible the expression of tttt with a parent with
only one "t" dose in very rare occasions.  *Garden Irises* had an extended
discussion of this, and I believe *TWOI* does also.

If the research is correct in what I have described above about the enzymes
twisting the ends of the Lycopene molecule, we get tangerine beards when the
formation of yellow *fails* due to a defect in the enzyme producing
alpha-carotene, and involved in the formation of beta-Carotene as well.

So how do we account for yellow irises having tangerine beards?  In the
irises that do have this combination, the yellow of the petal and the
"tangerine" of the beard do not look entirely normal, with the beard more
orange than red.  I doubt that a deep red beard on a yellow iris may even be
possible.

Have I confused the issue sufficiently?

Neil Mogensen  z 7  Reg 4 with another tropical deluge in progress (TD
Cindy) in the mountains of western NC

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