Purple podded snow pea project - some F2 questions

[templeton]

I've snuck in a winter growout of my Purple Podded X Snow Pea F2s. Plants are very crowded, and the first are just beginning to show pods. Luckily, I've got at least one purple podded to go on with.
But there are a few green podded showing as well. Since I'm after purple podded, and my snow parent already carries the A gene to turn anthocyanin on, I'm going to cull the green podded F2 plants to tidy up the patch, reduce disease, and make it a bit easier to see whats going on. Before I do so, just checking
1. my logic is right - if the pods aren't purple, the offspring never will be,
and
2. is there any reason i might want to keep some of the seeds off these as parents of potential crosses/back crosses or the like? I'm pretty sure there isn't but I wanted to check first.
T

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[Joseph Lofthouse]

Templeton: Was the photo of F1 or F2?

Aug 1, 2012 0:41:54 GMT -5 templeton said:

1. my logic is right - if the pods aren't purple, the offspring never will be

I don't remember if you told us what you want to get out of the project.... Are you after purple podded snow peas? Were the snow peas green podded? I think that purple pods are attributed to three dominant genes Pu, Pur, and A. Since all three are dominant genes, I think that you'd be safe tossing the green podded peas. However, purple pods also require the recessive genes for green pod, so if you used a yellow snow pea then that muddies the situation.

But, I also wonder if one or more of the Pu, Pur, or A genes is not actually dominant, but is perhaps penetrant and if the pod color is more intense with a double dose, or if there are other unknown genes that affect pod color. I say that because in my purple [podded] magnolia pea, I see mostly dark purple pods, and a few green pods, and a few pods with a purple blush. [The pods with purple blush look the same as F1 hybrids with yellow snow peas, and I grew them a few feet apart last year. Or perhaps peas aren't as utterly inbreeding as we have been lead to believe.]

[templeton]

The pic is of my F2 pods just coming.
Sorry Joseph, I should have been explicit - This particular cross I'm after a purple podded snow pea, with the parents a fibrous purple pod, and a big podded green snowpea (which has purple flowers so it must be carrying A).

I'm intrigued with your growout results - nearly all my F1 Green Snow (mum) X Purple Podded (dad) have given blotchy purple pods - I thought it was an environmental trigger - low light/temperatures not activating the anthocyanin somehow, but your results suggest otherwise.
So penetrant genes? tell me more.
T

[Joseph Lofthouse]

I am growing two of Kapuler's peas: A yellow podded snow and a purple snap (Sugar Magnolia).

The sugar magnolia seems to be segregating still because it throws green podded peas, and purple podded peas, and green pods with a purple blush. Perhaps 5% of my population this year were off-type. The off-type peas were high quality snap peas, so it doesn't seem like they crossed with a shelling pea or a snow pea. So I'm leaning towards an explanation based on the gene either being penetrant [incompletely dominant] (somewhere between dominant and recessive), or another unknown gene being present that regulates the amount of purple color in the pods.

I crossed the yellow and purple pea last year. The F1 looked like this when grown out.


The mother had the A gene as shown by the purple blossom:


The father also had the A gene:


My understanding is that in order to get purple pods, you also have to have an appropriate set of some of the recessive genes necessary for green pod. [My F1 can't have two copies of those since the mother was yellow podded.] At least one copy of the A gene was passed on to the offspring as shown by the purple flower. I presume that both the Pu and the Pur genes which are required for purple pod got passed on to the offspring, but the offspring are not deeply purple podded. I wonder if some deep purple will show up next year when I get a double dose of the Pu and Pur genes in some of the children, or whatever modifying genes are needed?

As far as the edibility of the cross went... The F1 was very fibrous and tough!!!

[templeton]

all my F1s look the same as yours - only a purple blush. But some of the more light-exposed pods or perhaps later ones - they were higher on the plant and got more sun - were purpler than the lower ones, thus my thoughts about enviro factors.
Trouble is, I can't remember how dark the original parents were.

Re the purple requiring green genes, I think it has to do with red over green giving purple, and A really providing the red bit rather than purple - if that makes sense.

I should go back and have a good read of Rebsie's blog.
T

[templeton]

Another F2 question - my F2 seed seems to be segregating into wrinkled 1/3, and non-wrinkled (or dimpled) 2/3.
see pic. actual ratio ratio (39:78). Should i be seeing segregation in the seed? I thought seed coat was a maternal characteristic, but I must say I'm not really clear on this. I can't remember if they came out of different pods. My initial thought was that they were just underdeveloped seeds because I harvested a bit early, but I'm not sure. Since wrinkled is thought ot be linked to sweetness, this would be a nice characteristic to be able to pick in the F2 seeds.
T

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[templeton]

and a pic of the seeds along with the parent seed - parents on left, F2s on right

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[Joseph Lofthouse]

Aug 6, 2012 17:59:41 GMT -5 templeton said:

Should i be seeing segregation in the seed? I thought seed coat was a maternal characteristic, but I must say I'm not really clear on this.

In corn, I see segregation in the seed-coat. I think that this is primarily due to interactions with the underlying triploid and diploid layers which are different than the maternal genetics of the seed coat. For example: I see segregation of seed-coat thickness based on the genetics of the embryo. And, if the endosperm changes size a lot while drying and is tightly attached to a somewhat thin elastic seed-coat, then the seed coat is likely to wrinkle to match the underlying endosperm. I see this in corn.

I think that peas may be similar.

[raymondo]

T, wrinkled vs non-wrinkled was one of Mendel's crosses. Yes, there will be segregation for this.

[templeton]

Aug 7, 2012 3:25:59 GMT -5 raymondo said:

T, wrinkled vs non-wrinkled was one of Mendel's crosses. Yes, there will be segregation for this.

Thanks Ray. Did a bit of G scholar, and found this quote re cotyledon colour and seed shape
"The first two of these traits are considered seed traits because they are observed in the seed cotyledons, which consist of embryonic tissue. Because each seed embryo is genetically a different individual, seed-trait phenotypes may differ among the seeds on a single heterozygous plant."
So it is possible to discern wrinkliness carriers from seed characteristic, before you sow. Good news, because as we discussed I've got limited growing space, and this gives me a selection characteristic for flavour, since wrinkles are linked to sweetness. I can pick out the wrinkly ones and just sow them, holding the dimples back if I don't get what I want out of the wrinkles.
T

[jim]

I think penetrance is being used out of context here, not quite accurately...incomplete dominance or blended inheritance might be more appropriate Joseph.
This is a quantitative trait, and I think you could expect green podded plants to have purple podded progeny, especially if you back crossed to a plant at least heterozygous for "A"
Jim

[templeton]

Aug 7, 2012 21:06:52 GMT -5 jim said:

I think penetrance is being used out of context here, not quite accurately...incomplete dominance or blended inheritance might be more appropriate Joseph.
This is a quantitative trait, and I think you could expect green podded plants to have purple podded progeny, especially if you back crossed to a plant at least heterozygous for "A"
Jim

Jim, thanks for the clarification

the JIC pisum gene database states the following for the Pur gene "Purple pods when together with Pu. Four alleles reported: Pur, uniform purple; pur<a, major part purple; pur<b, less colour on pod, may limit colour to funiculus. Character can be variable in expression and unstable. Studies have show that a pigmented funiculus differentiates the presence of Pur from Pu (non-pigmented)."
Given my understanding of genetics nomenclature is sketchy, does this mean there are 4 possibilities at that locus - Pur, pur<a, pur<b, and pur?
T

[Joseph Lofthouse]

Aug 7, 2012 21:06:52 GMT -5 jim said:

I think penetrance is being used out of context here, not quite accurately...incomplete dominance or blended inheritance might be more appropriate Joseph.

Thanks. Corrected previous post. That is so common with me...It's what happens when someone is self-taught in every facet of botany and genetics that they think they know... It's both helpful to me and a hindrance. Because I am free of the dogma about genetics that I would have been taught in school, but it creates barriers to understanding when I have came to different conclusions about genetics than what the dogma would lead others to believe...

As an example: I was so exasperated one day with my college aged daughter. Because she saw a cob of flour corn with segregating sweet corn kernels on it, and she insisted that the ratio would be 1:3 sweet to flour if they were counted. It was clear just by looking at the cob that the ratio was not even close to that. More like 1:20 She just could not grasp population dynamics. If there was only 3% sweet corn pollen that contaminated a patch of flour corn, then the ratios are not going to follow Mendel's laws of inheritance as applied to crossed homozygous inbreds. The segregation is going to be based on physical characteristics like the total population of contaminated plants in relation to non-contaminated plants, and bloom times, and prevailing winds.

Before I understood why, I used to be irritated with people that espoused Mendel's law of segregation. I realize today that it is because Mendel's segregation law only has practical application in very specialized circumstances: When two essentially homozygous cultivars are crossed and the offspring are selfed. There are just too many interactions going on within crosses of heterozygous populations for Mendelian genetics to be of much value to me as a landrace plant breeder. I understand today that Mendelian genetics is merely a stepping stone to introduce young students to a concept. Problem is that few ever go beyond that elementary school understanding, even in college.

[templeton]

It's an issue for education - or should i say, schooling - in general Joseph. Which is why engaged students (those who haven't been turned off by the system) who are really into learning love real world exercises. It's a dilemma - do we try to teach the whole complex system straight up, or try to introduce some organising principles so its not so confusing - but then relatively unrealistic in real world settings. I still struggle with it as an educator.
And ditto with the self taught genetics bit - I'm stumbling around a bit, despite my decades of 'book learnin'"
T

[templeton]

Found this interesting paper on purple colour genes in peas
<http://hermes.bionet.nsc.ru/pg/27/index.htm> downloadable pdf - it's the first paper.
T