Early results from cross-breeding Les Hannibal's Amaryllis

J.E. Shields jshields@indy.net
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

Jim Shields             USDA Zone 5             Shields Gardens, Ltd.
P.O. Box 92              WWW:    http://www.shieldsgardens.com/
Westfield, Indiana 46074, USA
Tel. ++1-317-867-3344     or      toll-free 1-866-449-3344 in USA

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