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Re: Broken Colour

Broken colour is indeed a tricky trait to pin down. The original work
by Alan Ensminger  produced BC only in crosses with plicatas after much
trial and error. And everyone since has followed his advice and been
able to produce BC from crosses of BC and plicata.  It is a separate
trait but needs specific conditions in order to be expressed.

First, consider that anthocyanin is a a dominant trait So we only need
one out of four genes to produce anthocyanin in a flower. When we have
no genes to produce anthocyanin, such as four  rra (recessive reduction
of anthocyanin) or four glaciata genes, then we have no anthocyanin. We
can also have  one gene for the dominant reduction of anthocyanin "I"
and it will repress functioning of anthocyanin.

The erratic expression of anthocyanin, that we call Broken Colour, is
actually a particular gene structure called a transposon. This is
sometimes called a jumping gene, but it is not the gene that is
jumping, but a segment of the gene that contains a "stop codon" This is
a DNA coding that stops the production of the biochemical being
produced , in this case the anthocyanin, This gene segment (transposon)
can move from one segment of the gene to another. When in one position
it can stop production of anthocyanin and it the other, it allows the
production. This can occur with the transposon  being in the gene that
produces anthocyanin or it can also be in a control gene such as the
"I" gene. To make maters more complicated is the fact that some
transposons (there are thousands of different ones) are independent and
others operate in pairs, a transposon and a facilitator gene (not
necessarily in same gene or even in the same chromosome). this
facilitator gene produces a chemical which allows transposon to be cut
so it moves to it's alternate location.

Now consider the production of anthocyanin to be like a dam with four
sluices which can be operated independently. If one of the anthocyanin
producing genes has a functioning transposon, then production of
anthocyanin will be sometimes turned on and sometimes turned off. This
will produce spots if turning off and on is rapid, or streaks if
turning off and on is slow. Now consider what  is happening in the
other four sluices. If even one of these is producing anthocyanin, then
the effects of the sluice controlled by the transposon will be less
noticeable or not even noticed.So for a transposon to be effective in
an anthocyanin gene  and to produce broken colour, then the other three
genes should not be producing anthocyanin. That is their suices are
closed to allowing anthocya into flower through.Thus a transposon with
other three anthocyanin genes being rra , will produce a broken colour.

Now, about plicatas and BC. Perhaps you have noted that all BC  with
plicata inheritence has anthocyanin in center areas. (Actually I do
have one with BC in rim area with center clear, but this is an
exception.) Also when one of these BC stop being a BC  you will have a
plicata with rim coloration  The transposon need s to be in either an
anthocyanin gene or an anthocyanin control gene, such as a plicata
gene. Now the question arises, what gene contains the transposon? It
has been suggested that these BC have three plicata genes and a jumping
gene. This does not fit what is known about how this works. It would
appear that one of the plicata genes contains a transposon. This would
work if the plicata  genes present were three glaciata genes and one
plicat gene with a transposon. This does seem to be the situation in
many of these plicata BC cultivars.  It probably isn''t the situation
in all cases. But when the transposon in any of these BC stops working
for a large segment we see a plicata pattern, so it would seem that the
transposon is in a plicata allele.

I'll stop here as this is already probably more then most people wanted
to know.

So to produce a BC you either needs plicat aroute or the rra route.

Of note, Louisa's Song if a Barry Blyth iris and one parent is a white
iris. Barry has a lot of plants with rra genes.

Of note, is  that a plant could have a functioning transposon in an
anthocyanin gene , but not show BC as it has other functioning
anthocyani production genes and the whole plant has anthocynin and the
BC pattern is covered up.

Chuck Chapman

Date: Wed, 24 Dec 2008 13:08:41 EST
From: RAINACRE@aol.com
Subject: Re: [iris] iris DIGEST V1 #746

Broken color has appeared spontaneously in my seedlings two or three
in the past 20 years. I have also worked with a number of broken  color
based on 'Maria Tormena' and 'Brindled Beauty'. Broken color is
independent of plicata. The bc factors seems to be randomly turned on
or off
during cell division and once turned on stays on in all the suceeding
produced from the initial turned on mother cell. Hence the streaks of
colorless or colored areas. A bc can be plicata and broken at the  same
time. In
sections of the flower where the bc is not working, the  plicata effect
seen. I think the idea that BC and plicata are connected may  have come
from the
fact that the first thing hybridizers thought of when  encountering BC
was to
cross it with plicatas because the bc factor looked like  plicata out
control. The broken color factor has the ability to reverse the  effect
of other
anthocyanin pattern factors in the  wedge of tissue in  which the bc
factor is
turned on. Thus a bc factor in a variety with white  standards, and
blue falls
can give white standards streaked with blue and blue  falls streaked
white. Wow, that's bit too much to think about on Christmas  Eve.

As the result of crossing my  bc line with 'Louisa's Song' I will be
introducing a broken color which is over 36" with a large flower and
quite  enough
buds. Introduction 2010 or 2012.

Fred Kerr
Rainbow Acres

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