Re: HYB: ?heredity of orange questions?

To have an orange you must have tttt to start with. Plus the genes for alternative yellow, in four copies. The same way you can't have tangerine without four copies of t, you can't have the alternative yellow without four copies of it's gene.
If you cross a pink (without any copies of recessive yellow genes, or recessive removal of lycopene from petals) ) to an orange, all seedlings will be pink. So... orange is recessive to pink.
Of note, the concept of an orange iris having one orange cartenoid pigment is not supported from any analysis of pigment, and is an assumption leading to concept of pink to orange to yellow. Test crosses do not support this concept either. Pink is dominant to orange, but this concept is just looking at phenotype. 

Now looking at genotype.
But actually what is occurring is that the alternative yellow (a different set of genes then regular yellow) is a recessive, and completely independent from tttt. So both alternative yellow and tttt are inherited separately and are not alleles. So.. you have to look at these separately
To get an orange you need both Alternative yellow , plus tttt. Regular yellow and tttt are alleles and yellow is dominant over tttt. No effect of alternative yellow on inheritance of tttt and vice versa.
Any pink from a cross having one orange parent will carry two copies of the alternative yellow genes and crossed with an orange will give 1/6 orange seedlings.
The degree of saturation, ie total coverage to produce solid orange, will depend on modifier genes. The more solid orange the parents, the more solid orange the offspring. The more they are peach or apricot or wash, the more wash will be the offspring. I haven't kept records on this so just postulating here.
Crossing a white with tangerine beard to an alternative yellow with tttt beard will give all white with tangerine beard (given that there are no recessives alternative yellow genes in the white with red beard.)
Crossing a yellow with tangerine beard to an orange will produce all orange, barring those pesty recessives.
So to predict crosses, check parentage to get an idea on genes present. Focus on alternative yellow, tttt, and the recessives that remove cartenoid expression in petals (those that give yellow or white with red beards.) the recessive genes that give white with pink beard won't effect the alternative yellow . just regular yellow and lycopene. 

All this is assuming that we don't have to deal with anthocyanin.

Hope this adds some clarity and not more confusion

Chuck Chapman


Date: Tue, 06 Jan 2009 09:23:23 -0500
From: Linda Mann <lmann@lock-net.com>
Subject: [iris] Re: HYB: ?heredity of orange questions?

Thanks for going over all of that (again?), Chuck.

But I'm still not sure I understand how orange is inherited, or rather
how to guestimate probability of getting orange from various types of
crosses.

Paul's version is easy (easier!) to understand - pink is recessive to
orange which is recessive to yellow.

But I'm still confused as to whether there are <two> or <three> sets of
genes at work - tttt and carotenoid yellow (i.e., absence of reduced
carotene genes) <or> tttt, yellow , and a third thing that causes
partial yellow <and> tttt to give orange?

Not to forget reduced anthocyanin set of genes
Maybe my brain is simply not quite ready to wrap around this one yet. I 
may have to wait & see the babies bloom....
- --
Linda Mann east Tennessee USA zone 7/8

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