Early results from cross-breeding Les Hannibal's Amaryllis
J.E. Shields (Mon, 13 Sep 2010 05:40:14 PDT)

Hi Mike,

I'm a retired biochemist, not a geneticist, so I'll have a pretty
superficial take on these things. Here is my analysis:

It's like Rodger said.

--The ratio of pink to white flowers implies that pink color is dominant
over white color.

I agree, normally pigment (pink, red, orange, etc.) is dominant or
partially dominant over white.

--However, I don't know what to make of the fact that the pink shades
average out when they're crossed, rather than one being dominant over the
other. What is this telling me?

This tells you that there is more than one gene locus involved in the pink
pigment expression.

--The fact that I got some whites by crossing two pinks implies that both of
those pinks had recessive genes for white, right? Since one of the pinks I
crossed was my darkest pink, I don't know whether any of my bulbs have pure
pink color genes in them.

In many cases, I would expect pink to be heterozygous for red (or dark
pink) and white -- in the simplest cases anyway.

That is, white flowers result from a homozygous condition where both
alleles for one of the genes making pink pigment are defective. Light pink
would result from crossing dark pink (homozygous for pink pigment) with
white. Crossing two light pink plants would give 1 : 2 : 1 ratio of dark
pink : light pink : white offspring. This is the simple case. Your cases
don't seem simple.

--I can't figure out how a cross of a pink and white flower would produce
all white flowers, unless in this case white is dominant. But could a gene
be recessive in some cases and dominant in others?

I suspect your 50 parent plants have among them a variety of different
genes producing pink and white. One way White could be dominant would be
for it to produce a microRNA that killed the system for making pink pigment.

Remember that there are structural genes, which code for enzymes which
actually make the pigments -- anthocyanins in the case of red, pink,
orange, purple -- and there are regulatory genes which turn other genes off
and on.

You have a heterogeneous population with a mix of different genes producing
pink and white flowers, and you would have to analyze pairs of parents in
isolation to eventually sort them out. At 10 years per generation, I hope
you are a teenager!

Jim Shields
Not a teenage

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