[evilunclephil]

Found this in a book I never noticed before in the study, "Genetics Notes, 7th Edition" by James F. Crow

"Inbreeding, by increasing the homozygosity, brings out the detrimental genes that were previously concealed by heterozygosis with more favorable dominant alleles. It is usually impossible, even by the most rigid selection, to rid an inbred line of all detrimental recessives, so a decline in vigor, yield, and survival are almost inevitable consequences of inbreeding. At the same time inbreeding increases the uniformity by decreasing the number of segregating loci.
One way to attain a high yield and vigor, and at the same time have genetic homogeneity, is by crossing two homosygous (or nearly so) inbred lines. The hybrid is uniform, since all the plants are identical, yet each of them is highly heterozygous. This is the basis of hybrid corn.
Evidence is accumulating that some of the increased yield in the best hybrids is due to factors other than the covering of harmful recessives. There are some overdominant loci at which the heterozygote, A/a, is superior to either homozygote, A/A or a/a. How important such loci are for economic characters like yield in corn is unknown.
By inbreeding it is possible to get corn strains with desirable attributes, such as proper ear shape, sugar content, color, and resistance to disease. Then two inbred strains are crossed to get the increased yield that results from heterozygosity. The only difficulty with this scheme is that the corn seed that is sold for planting is grown on inbred plants; this cuts down the yield and makes the seed expensive. This difficulty is circumvented by using four-way crosses. Inbred lines A and B are crossed to produce hybrid AB; C and D are crossed to produce CD; then the two hybrids are crossed. The resulting four-way hybrid is just about as high yielding as the single cross, and though somewhat more variable, is satisfactory for commercial purposes.
Hybrid corn is produced from specially bred hybrid seed, and the seed has to be purchased anew each season. The following data shows the decline in yield when a field of hybrid corn is allowed to pollinate at random and then these seeds are planted. A three-way cross is a cross between a hybrid and an inbred, AB x C.

Table 21-1
Yield in bushels/acre (data from N.P. Neal)

_____________inbred lines_____________Randomly____ _______________
_____________from which_____________pollinated__ _________F after
_____________hybrids derived___Hybrid__from_______P arent__random
________________(F = 1)______(F = 0)__hybrids____decline__pollin ation
Single Cross___23.7____________62.8__ __44.2_______47.6____.50
Three way____23.8____________64.2___ _49.3_______36.8____.375
Four way_____25.0____________64.1__ __54.0_______25.8____.25

Notice that the decline in yield is almost exactly what would be expected from the inbreeding coefficient."

There's also sections on "The Coefficient Of Inbreeding, F" and "Computations Or F From Pedigree", and "Empirical Data On Inbreeding And Estimates Of The Amount Of Hidden Genetic Damage Due To Recessive Genetics" and I will TOTALLY copy them over if you guys think it would be helpful information.

tagged

[blackone]

Interesting to see how 4-way crosses - and even offspring of four-way crosses are a lot better than offspring of single crosses.
Please do copy the other sections, this is good stuff.

[evilunclephil]

Think I should make new threads for the other subjects? There's also an extensive portion of the book relating to selection for traits, both sex based, and non sex based, dominant, and recessive.

[Raco]

Very interesting
How do compare corn and cannabis when it comes to breeding?
Buenos dias Tom!! :wink:

[Raco]

Thanks Tom,
yes I remember...in fact,I printed all that and still have it.

"Well, my main concern is maintaining pure lines & it will be a cold day in hell my friend before I'll let general or specific combining ability be the driving force behind my IBL breeding efforts"

Well said!!
your lines rock
no matter what they say...
hybe´s b.s....jejeje!!
It rains a lot this summer...the corn is nearly 3 meters tall around here

[masterlow37]

Originally Posted by TomHill

Well, my main concern is maintaining pure lines & it will be a cold day in hell my friend before I'll let general or specific combining ability be the driving force behind my IBL breeding efforts.

I love your thinking Tom Hill !!!

Peace

[B.C.]

Keepin an open mind is how we learn new things. After all,if one claims ta know it all,it surely means that he doesn't.Good thread! Take care...BC

[evilunclephil]

It's good to know more about this than what is just in the book, thanks TomHill. There's a couple more sections I'd like to copy as well, but some, like the subject pertaining to the computation of F I don't fully understand. Seems like this is the right forum to share this info in and get great feedback though!