Post by raymondo on Jun 14, 2011 8:24:31 GMT -5
Rebsie's marvellous red podded pea seems to have inspired a number of people to have a go at creating their own, me included. I hope those interested find the following useful.
There is one gene at work for the green vs yellow pod and there are, it seems, three genes at work for the purple pod, an on/off switch plus two colour genes. Lets call them A, B, C for the purple and D for the green. If all three purple genes need the dominant alleles (I'm not 100% sure about this), a true breeding purple must be AABBCCDD, that is, homozygous dominant at all four loci. A true breeding yellow could have a number of genotypes but the worst case scenario for a breeder interested in creating red pods would be aabbccdd, that is, all homozygous recessives.
So, the first cross, in the worst case scenario, is a cross of homozygous dominants for all four genes (purple) and homozygous recessives for all four genes (yellow) - AABBCCDD x aabbccdd. This means that the F1 generation will be heterozygous for all four genes and all purple podded - AaBbCcDd. This exactly what Rebsie found (daughterofthesoil.blogspot.com/2008/03/real-seeds-purple-mangetout-pea-project.html).
For the F2, a Punnett square is way too messy as it will have 16 (4 genes each with 2 alleles or 24) possible gametes producing no less than 256 possible zygotes. Instead, let's calculate the probability of getting a red-podded pea in the F2. You want at least one dominant allele in each of the three purple gene slots and you want both recessive alleles in the green pod slot. The probability of getting at least one dominant is 3/4 at each of the purple slots. The probability of getting both recessives in the green slot is 1/4. So, the total probability of getting a red pod is 3/4 x 3/4 x 3/4 x 1/4 = 27/256. So, 27 out of your 256 possible outcomes will have red pods. That's a little more than 10% which is pretty good.
Of course, most of these will be heterozygous at one or more of the purple pod slots so in subsequent generations you'll get plenty of yellows showing up. You'll need to do some family line selections to eliminate the recessives here. You won't have to worry about green pods showing up because all the F2 reds that you started with will be homozygous recessive in the green slot.
All of the above assumes independent assortment. Then of course there's the issue of pod type - shell/snow/snap!
The way I intend to go is to do deliberately what Rebsie did by chance. At the same time that I do my purple/yellow cross, I'll do a green/yellow cross looking for a better yellow. Then, if needs be and I have to cross the red into a yellow to get the right pod type, I should have a good one to use.
I hope this helps rather than hinders.
There is one gene at work for the green vs yellow pod and there are, it seems, three genes at work for the purple pod, an on/off switch plus two colour genes. Lets call them A, B, C for the purple and D for the green. If all three purple genes need the dominant alleles (I'm not 100% sure about this), a true breeding purple must be AABBCCDD, that is, homozygous dominant at all four loci. A true breeding yellow could have a number of genotypes but the worst case scenario for a breeder interested in creating red pods would be aabbccdd, that is, all homozygous recessives.
So, the first cross, in the worst case scenario, is a cross of homozygous dominants for all four genes (purple) and homozygous recessives for all four genes (yellow) - AABBCCDD x aabbccdd. This means that the F1 generation will be heterozygous for all four genes and all purple podded - AaBbCcDd. This exactly what Rebsie found (daughterofthesoil.blogspot.com/2008/03/real-seeds-purple-mangetout-pea-project.html).
For the F2, a Punnett square is way too messy as it will have 16 (4 genes each with 2 alleles or 24) possible gametes producing no less than 256 possible zygotes. Instead, let's calculate the probability of getting a red-podded pea in the F2. You want at least one dominant allele in each of the three purple gene slots and you want both recessive alleles in the green pod slot. The probability of getting at least one dominant is 3/4 at each of the purple slots. The probability of getting both recessives in the green slot is 1/4. So, the total probability of getting a red pod is 3/4 x 3/4 x 3/4 x 1/4 = 27/256. So, 27 out of your 256 possible outcomes will have red pods. That's a little more than 10% which is pretty good.
Of course, most of these will be heterozygous at one or more of the purple pod slots so in subsequent generations you'll get plenty of yellows showing up. You'll need to do some family line selections to eliminate the recessives here. You won't have to worry about green pods showing up because all the F2 reds that you started with will be homozygous recessive in the green slot.
All of the above assumes independent assortment. Then of course there's the issue of pod type - shell/snow/snap!
The way I intend to go is to do deliberately what Rebsie did by chance. At the same time that I do my purple/yellow cross, I'll do a green/yellow cross looking for a better yellow. Then, if needs be and I have to cross the red into a yellow to get the right pod type, I should have a good one to use.
I hope this helps rather than hinders.
) I have begun breeding tomatoes this year. I made 10 crosses this year that set fruit. I have my F1's in the greenhouse right now. I am seeing successful confirmation in some of the F1 phenotypes. I will have to wait to see the others when the fruit has set or ripens. I am looking forward to this next garden season. I would like to try my hand at breeding to improve tomatoes, peppers, cucumbers, melons, squash and more! I love to garden and watch stuff grow. I really enjoy the good and wholesome food for my family! I am a seed saver and I like to share seeds. The greenhouse and the garden is a good place for me to find my zen. 
After reading this thread I am eager to work with edible pod peas. I have read that the sugar snap pea arrived from a cross between the garden pea and the edible pod pea. Is this the case?
Thank you,