It is also important to think of genes as existing in populations. How good an allele is depends very much on the other genes present. There is a very interesting instance of moths not behaving as expected when moved from one gene pool to another.

The Lesser Yellow Underwing moth is normally yellowish brown but there is a variant, which is blackish (curtisii). The variant is not found in England but co exists in Scotland and the Isles with the normal variant (comes). The curtisii dark colour pattern is nearly completely dominant to the normal comes pattern.
 

The hybrids between the two look like the curtisii even though they bear the genes of both. Ford (Oxford) caught specimens of the moths from various islands and the Scottish mainland. Evidence showed that the curtisii gene was dominant on the island and mainland. Based on this it was expected that when the moths from different islands were mated that the normal dominance pattern would hold. But it never and the curtisii dominance completely disappeared and a complete range of intermediaries turned up in the hybrids, as if there was no dominance. The conclusion was that the curtisii gene should only be thought of as having its effects in the presence in a context of a suite of other genes. Some of which it switches on. The above is mentioned by Richard Dawkins in his book Unweaving The Rainbow, which is some good recommended reading.

This idea will be important when looking at various bloodlines found in predominately different areas of the globe. Just how good the genes perform when transported from one region to another may well be dependent on local racing conditions and the bloodlines found in that region.

By way of illustration, a line that may be successful in North America on dirt tracks may have difficulty in performing at the same level in Australasia where the broodmare population is best at producing turf horses. The characteristics for success on dirt may vary from what is required to perform on turf surfaces and vice versa. How genes are expressed, being dependent on the genes present in the local population.

Mr Prospector and Sir Ivor might well fall into this category. Mr Prospector  has disappointed to date, as a sire prospect in Australasia and it might be that his gene pool is not that well suited to the Australasian broodmare. On  the other hand in NZ we have done reasonably well with some bloodlines that have disappointed elsewhere. Sir Ivor, comes to mind. That is, to get the best out of a set of genes they need to be in the right gene population and environment.

Some horses seem best suited to bloodlines found in different regions. Like everything to do with breeding there will be some notable exceptions. It is essential that you treat your breeding stock as unique individuals.