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Re: HYB: Blyth Iris


John Montgomery wrote:

>  Nested recessives?
>  I don't recall coming across this term before. Would you please explai=
n?

In the strictest sense, it's a picturesque term for the effects of
hierarchical dominance, which lets us focus on the practical aspects of
working with such lines without getting bogged down in a detailed genetic=

analysis of the traits.  Not to discourage exploration of the mechanisms
involved by those skilled in genetics -- but a lot can be accomplished by=
 a
pragmatic approach when there's not enough information for rigorous
experiments.

You can think of "Nested Recessives" as recessives within recessives.  Ki=
nd
of like a set of luggage in which the small bags fit inside the
medium-sized one and that one fits inside the largest, so that the whole
set can be stored inside the largest bag.  But you don't know until you
open that large bag which, if any, of the smaller ones were stored inside=

it.

The sequence of anthocyanidin self >white-ground plicata > recessive whit=
e
is the most widely used example.  A self may contain plicata or ice genes=

-- but you can't tell by looking at it.  If you breed out the self genes,=

leaving what you might think is homozygous recessive plicata,  there may =
be
ice genes lurking within that plicata.  Again, you don't know what's ther=
e
until you examine its breeding behavior.  The recessive white, or plicata=

ice, or glaciata -- depending on which term you prefer -- is recessive to=

the plicata, which is in turn recessive to the self.  Nested, in other
words.  =


In a looser sense, the term "Nested Recessives" can be used to describe t=
he
sudden appearance of a new color or pattern in a line previously believed=

to be homozygous recessive.  Like Blyths red-bearded blacks from pink
amoenas.  I'm sure the purists would rather know whether it's truly a
previously unknown allele or an uncovered interaction or modifier -- but
because we still know so little about the detailed genetics of iris, the
pragmatic approach has its place.

Sharon McAllister
73372.1745@compuserve.com





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