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Re: HYB: color genes made easy (orig post 7/17/97)


Thanks so much for finding this for us, Linda.  I've printed it out 
and will study it along with other input.  I wouldn't hold my breath 
until I understand it, but I'm very grateful to have it.  With each 
study, I get a little closer.

Patricia Brooks, Iris Addict


--- In iris-talk@egroups.com, Linda Mann <lmann@i...> wrote:
> Turns out Tom Little's post wasn't about Punnett's square after 
all -
> sorry for the confusion.  Took some serious searching even when I 
knew
> what I was looking for and I had to go to my printed copy to find 
it, so
> figure it's worth posting again.  Here is the original post:
> 
> 1. GENES THAT DETERMINE IRIS COLOR
> 
> Beware: I've made a few simplifications for the sake of 
conciseness. And
> 
> only genes found in TBs are considered.
> 
> 1a. Genes Affecting the Blue and Purple (Anthocyanidin) Pigments:
> 
> V (dominant), allows the flower to produce purple pigments
> v (its recessive), no purple pigment produced
> 
> I (dominant), inhibits the expression of purple pigments everywhere 
in
> the
> flower
> i (its recessive), lets the purple be expressed
> 
> I-s (dominant), inhibits or reduces the expression of purple 
pigments in
> 
> the standards
> i-s (its recessive), lets the purple be expressed everywhere
> 
> PL (dominant), lets the purple be expressed everywhere
> pl (recessive to PL, dominant to pl-a), lets the purple be expressed
> only
> along veins and petal edges (plicata)
> pl-lu (recessive to PL, dominant to pl-a), lets purple be expressed 
only
> 
> between veins, leaving clear veins, styles, and hafts (luminata)
> pl-a (recessive to PL, pl, and pl-lu) prevents the expression of 
purple
> 
> 1b. Genes Affecting the Yellow and Pink (Carotenoid) Pigments:
> 
> Y (dominant), allows the flower to produce yellow pigments
> y (its recessive), no yellow pigment produced
> 
> [Note--the situation with yellow is more complicated than this. 
There
> are
> probably several genes involved; simple dominant/recessive model 
may not
> 
> always work.]
> 
> H (I just made this symbol up), causes the yellow pigment in the 
falls
> to
> be distributed in a "halo". I don't know if this is dominant or not.
> Some
> breeders may want to chime in.
> 
> A (I made this one up too), allows yellow pigment to be distributed
> throughout the flower
> a (its recessive), causes yellow pigment to be eliminated or 
reduced in
> the
> standards.
> 
> T (dominant), keeps pigment in its yellow form
> t (its recessive), changes yellow pigment to pink
> 
> 2. GUESSING YOUR IRISES' GENES
> 
> Here are some rules to help you guess which of these genes a given 
iris
> may
> have. You'll need to view this using a fixed-spaced font. An "x" 
means
> at
> least one copy of the gene is probably present, a "o" means none of
> these
> genes can be present. (Since TB irises are tetraploids, there is a 
total
> of
> four of each type of gene.)
> [for these tables, to get them to line up right, try using courier 
or
> other fonts - lm]
>                                    V   I   I-s Y   A   H   T   PL  
pl
> pl-lu
> 2a. Selfs:
>     blue or violet                 x   o   o   o               x
>     red, brown, or black           x   o   o   x   x   o   x   x
>     yellow                             x       x   x   o   x
>     pink or orange                     x       x   x   o   o
>     white                              x       o
> 
> 2b. Bicolors:
>     purple or blue amoena          x   o   x   o               x
>     yellow amoena                      x       x   o       x
>     pink or orange amoena              x       x   o       o
>     variegata                      x   o   x   x   x       x   x
> 
> 2c. Plicatas
>     blue or violet on white ground x   o   o   o               
o       o
> 
>     red or brown on yellow ground  x   o   o   x   x       x   
o       o
> 
>     violet on pink/orange ground   x   o   o   x   x       o   
o       o
> 
>     no plicata markings on standards (various ground colors)--same 
as
> above,
>         but at least one I-s
>     luminata (various ground)      x   o   o                   o   o
> 
> 2d. Halos
>     yellow stadards, falls white w/yellow halo (e.g., Debby Rairdon)
>                                        x       x       x   x
>     pink standards, falls white w/pink halo (e.g., Queen of Hearts)
>                                        x       x       x   o
>     brown standards, falls violet w/brown halo (e.g., Brown Lasso)
>                                    x   o   o   x       x   x
> 
> If you study the chart for awhile, you'll find you get the "feel" 
of it,
> 
> and can guess the genes of color combinations not on the chart. For
> example, 'Broadway' has clear yellow standards, and white falls with
> red-brown plicata markings. It must have V (because the plicata 
markings
> 
> are made with the purple pigments, not the yellow ones), it cannot 
have
> I,
> it must have I-s (because there are no purple markings in the
> standards),
> it must have Y, it must have H (because the center of the falls are
> white,
> but there must be some yellow around the halo to account for the 
redness
> of
> the plicata marks), it must have T (because the yellow is yellow, 
not
> pink), and cannot have PL or pl-lu.
> 
> 3. WHEN YOU CROSS 'EM
> 
> As you can see from the chart above, in most cases we only know 
whether
> a
> particular dominant gene is present (at least one) or absent 
(none). We
> usually don't know exactly how many copies of a dominant gene may be
> there.
> But if we're just making an "educated guess" of what might come out 
in
> the
> seedling patch, that's good enough. Here are the rules:
> 
> 3a. If neither parent has a particular dominant gene, NONE of the
> offspring
> will have it. Thus crossing two plicatas can never produce a violet
> self,
> because neither parent has the PL gene needed to make this happen.
> 
> 3b. If only one parent has a particular dominant gene, AT LEAST 
HALF of
> the
> seedlings can be expected to have it too, on average. (If more than 
one
> copy of the gene is present, it may appear in most or all of the
> seedlings.)
> 
> 3c. If both parents have a particular dominant gene, AT LEAST 3/4 
of the
> 
> seedlings can be expected to have it too, on average.
> 
> Using these rules, you can make a good guess which of the dominant 
genes
> 
> the seedlings may end up with, and predict their color patterns.
> 
> 4. GETTING FANCY
> 
> If this is not enough fun, and you want to get a better idea of how 
many
> 
> genes of each type the parents may carry, you need to do pedigree
> research.
> If an iris comes from crossing a violet self and a plicata, for 
example,
> I
> know it can have at most two PL genes out of its total of four; the
> other
> two (which came from the plicata parent) are almost certainly pl. In
> this
> way, you can sometimes narrow down the possibilities of what 
recessive
> genes may be present, and in what dosage.
> 
> Ultimately, of course, if one knows the full genotype of the 
parents,
> one
> can calculate in detail the percentages of seedlings having each
> possible
> genotype. Genetics books have instructions and exercises for this 
sort
> of
> thing.  In practice, though, we hardly ever know the complete 
genotype
> of
> the parents, and we rarely care about the exact percentages that 
might
> appear in the seedling bed (the exception being with controlled 
crosses
> designed to study how a particular trait is inherited).
> 
> These "rules of thumb" are a _lot_ easier to use than the 
computations
> that
> are explained in the textbooks, and in most cases give a very good 
idea
> what to expect from a cross.
> 
> Happy irising, Tom [Tadfor Little]


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