Exploring the Sporthorse Database…I hadn’t heard this term before. Can someone please explain?
How important is it when looking a potential mating?
Ancestor loss is another way of looking at the “inbreeding” in the pedigree (inbreeding used here as amount of the same blood in the pedigree).
Used in an example, looking at Quinar:
Sport-horse data reports Ancestor Loss 6 generations as 13.49%. This is calculated through…Percentage of Different Ancestors=100% - Ancestor Loss.
In this case, over 6 generations Quinar has 110 unique ancestors out of 126.
Ancestor loss is calculated by: 100%-(110/126 *100) = 12.69% The reason that this does not match up exactly is because the 6 generation pedigree is deemed incomplete and the unreliable factor must be added in.
If you look at Quinar’s dam Adele you will see that she has 100% unique individuals in her 6 generation pedigree leading to the reporting of a 0% ancestor loss.
The basic concept (used heavily by greyhound breeders) is that, the higher the percentage, the more inbred the horse.
Recombination is what keeps it a bit of a unknown in any one case.
Image a red horse and a blue horse. So the red horse gives 10 red marbles to her foal and the blue horse give 10 blue marbles to the same foal.
The foal (named Sam) has 20 marbles, 10 red and 10 blue. Sam has a foal, so Sam reaches in her marble bag and randomly (almost) pulls out 10 marbles. She might grab 5 blue and 5 red or 1 blue and 9 red or anything in-between. So lets say she grabs 2 red and 8 blue. The resulting foal, only has 2 red and may or may not pass those 2 red onto the next generation. Likewise, the resulting foal has 8 blue and may pass 7 onto her foal when she reaches in her bag. Within 2 generations, the red and blue horse cross may have significantly genetically varied grand children. This is why full siblings can be so incredible different.
Line breeding just stacks the bags in favor of a certain horses genes and cuts down on the addition of other genes. But it is still a random process on what is passed on. If you breed Sam back to her brother, then the odds are higher.
Loss of genetics over 2 gens can be substantial and is not consistent. The formulas they use are like the xx blood, they are just very rough estimates of what could come through. But if you select the offspring that are more like one parent or another you are adding selection to the “randomness”. All of those numbers are very rough to the point of meaningless after 2 or 3 generations.
So does one prefer a high % of Ancestor Loss or a low one? Or does it just depend on if you are a fan of linebreeding or not?
I have an art background. So why aren’t any of the crosses PURPLE?:winkgrin:
[QUOTE=Kyzteke;7190952]
I have an art background. So why aren’t any of the crosses PURPLE?:winkgrin:[/QUOTE]
That is a good question. Think cheese strings instead of paint.
The overall horse may be more purple than blue or red.
[QUOTE=Kyzteke;7190949]
So does one prefer a high % of Ancestor Loss or a low one? Or does it just depend on if you are a fan of linebreeding or not?[/QUOTE]
To be honest, I would not really look too much at the % Ancestor Loss. It is an interesting number to see at a glance, but it really does not give you enough information to be really useful in making actual breeding decisions. Fun to play with in test matings, but stoicfish indicated part of the reason that it is a very crude measure to use in actual practice. Furthermore, it is just a proportion and really does not keep in mind the distance back from current generation or blood beyond the calculated genealogy (ie it presents all consanguinity as equal regardless of how far back in the pedigree it occurs).
A more interesting number to look at when doing test matings, imo, is the Coefficient of Inbreeding (Sewall Write’s Coefficient of relationship), which is the probability that at a random locus, the alleles there will be identical by descent. This explores the expected percentage of homozygosity arising from the breeding. However, again whenever using measures of population genetics, one must remember that the individual is often much different than the population and you will only be looking at averages.
It is a much better practice to be informed about the blood you are wishing to use and to understand what traits are more prepotent than others and decide if this is something you wish more of in your resulting offspring.
[QUOTE=stoicfish;7190921]
Recombination is what keeps it a bit of a unknown in any one case.
Image a red horse and a blue horse. So the red horse gives 10 red marbles to her foal and the blue horse give 10 blue marbles to the same foal.
The foal (named Sam) has 20 marbles, 10 red and 10 blue. Sam has a foal, so Sam reaches in her marble bag and randomly (almost) pulls out 10 marbles. She might grab 5 blue and 5 red or 1 blue and 9 red or anything in-between. So lets say she grabs 2 red and 8 blue. The resulting foal, only has 2 red and may or may not pass those 2 red onto the next generation. Likewise, the resulting foal has 8 blue and may pass 7 onto her foal when she reaches in her bag. Within 2 generations, the red and blue horse cross may have significantly genetically varied grand children. This is why full siblings can be so incredible different.
Line breeding just stacks the bags in favor of a certain horses genes and cuts down on the addition of other genes. But it is still a random process on what is passed on. If you breed Sam back to her brother, then the odds are higher.
Loss of genetics over 2 gens can be substantial and is not consistent. The formulas they use are like the xx blood, they are just very rough estimates of what could come through. But if you select the offspring that are more like one parent or another you are adding selection to the “randomness”. All of those numbers are very rough to the point of meaningless after 2 or 3 generations.[/QUOTE]
What a really great way to explain it!
In the world of the TB it’s very common for MANY horses, maybe most, to have 70% or more ancestor loss in twelve generations. That means that the “real” gene pool is very limited.
In fact, I read a blurb about a study that said that 70% of TB genes come from 27 stallions. When you think about the fact that 95% of all TBs trace back to one sire line, this number seems to show that the 27 stallions persist mainly through their female descendants. Another interesting TB factoid is that another study showed that one of the three sire lines that is hanging on by a thread is Herod who provides approximately 17% of all genes in the modern TB --and he derives from the earliest of the three foundation sires.
Elles recently posted that Northern Dancer, the epitome of the modern TB, has 19.80% Herod–and Herod was a foal of 1756 with approximately 100 foals.
I’m not quite sure what all this means, but it’s interesting to me.
It seems to me that the point of linebreeding is to maximize the chances for homozygous traits, which means that the trait will be expressed in the foal.
