Every horse has a tail male line and a tail female line, no matter where it is in the pedigree. Tail female is important in each horse because the mitochondrial DNA comes only female to female to female, to the beginnings of time. Since there are many variants of MtDNA, which control cellular energy production, some MtDNA might work better with particular genetic codes than with others. That’s work still to be done.
Tail male isn’t that important according to current knowledge because there are only 4 Y variants among all horse breeds and they vary only a little. No one is quite sure what the variants affect, but all horses that trace back to Whalebone tail male have a slightly different Y than non Whalebone line tail male horses. Most of the non-Whalebone horses in the West have a variant that is similar to, IIRC, Oriental (Middle Eastern) horses. That means that in Thoroughbreds and horses with thoroughbred tail males, the King Fergus line of Eclipse, Herod and Matchem have very slightly different Ys from the dominant Whalebone line. The Y chromosome passes unmodified from male to male to male. As I remember the scientific paper that made this announcement, Standardbreds and many QHs have the non-Whalebone variant. Whether or not there is a benefit to the Whalebone Y, it has come to dominate the TB and the WB. The Y is the smallest chromosome by far.
The mitochondria and the Y are how genetic historians go back in time.
The sire’s X passes intact from him to his daughters. His sons don’t get it, of course. A female’s X from her dam and to her children is subject to recombination during the egg formation process. so her eggs will will be a mixture of her dams’ genes from the dam’s sire and dam and her’s sires intact X. If the sire’s X is the active one in the filly, she will take after her paternal granddam and the granddam’s damsire, at least as far as the X goes–and it’s by far the largest of the chromosomes and still not understood by scientists. But all her eggs will be recombined.
Theoretically, all of the horses in every position in a pedigree would have equal influence (barring epigenetic effects) since all the other genes will recombine and be a mixture of sire and dam. Only the sire’s X and Y pass unmodified from him–and the MtDNA from the dam.
But a sire and dam can only pass on the genetic material that they receive, so even if the recombination doesn’t produce a 50-50 split, the parents should still have the most influence. And, of course, we are still learning about “junk” DNA, how genes turn on and off, and epigenetics. There are some studies that indicate that genetic material from grandparents that is in the “junk” can suddenly turn on in grandget. It’s all very complicated and very much subject to the laws of chance, since recombination is still more random than not, within limits.
I personally think, although without much knowledge to back it up, that we will discover that the X and Y chromosomes from the sire have more influence in genes throughout the genome turning on and off than current knowledge is able to verify. I speculate that this is so because pre-potency exists, the VERY long history of animal breeding that focuses on the males, and the fact that broodmare sires really do exist.
[QUOTE=twelvegates;7316212]
Thanks for starting this thread weixaio.
Continuing just a bit of the spin-off about the terms used in TB ancestry.
If I understand correctly, the tail male is the “top line” of the pedigree and the tail female is the “bottom line” of the pedigree? So I just keep following that sire who is at the very top of the pedigree through the 5th generation, click on the 5th generation sire, and follow him back and continue this pattern, to trace the tail male lineage? (And the opposite for the tail female: i.e., choose the dam who is at the very bottom of the pedigree through the fifth generation and keep following that line back.)
What is the particular significance from a genetic point of view to following these two lines, as opposed to branching into others. Maybe I have it all wrong, but it seems the WB breeders look to the sire, dam, then damsire for influence. But this would not be the same as following tail male and tail female, correct?[/QUOTE]
