Genetic linkage between the loci for phosphohexose isomerase (PHI) and a serum protein (Xk) in horses.

This research article is about the discovery of a genetic connection between the genes responsible for the enzyme phosphohexose isomerase (PHI) and a blood protein (Xk) in horses, thereby adding to the understanding of equine genetics.

Genetic Linkage Discovery

The study found a genetic linkage, or connection, between two specific genes in horses – the one which codes for an enzyme phosphohexose isomerase (PHI) and another which produces a serum protein (Xk).

• This finding is based on the genetic data obtained from three separate sire, or father, families. The scientists were able to trace the inheritance of these genes, demonstrating that they often appear together in the same individuals.
• These two genes are not independently assorted. The researchers estimated a recombination frequency of approximately 0.23 meaning that, during meiosis, these two genes have a roughly 23% chance of being separated and passed on to offspring independently of one another. The closer together the genes are on the chromosomes, the lower the recombination frequency would be.

Sire Diversity and Potential Linkage Group

• An interesting note was the heterogeneity observed between the sire families in terms of the recombination frequency. It suggests that, while the linked genes are generally passed on together, the exact likelihood of independent assortment varies from individual to individual.
• No links were discovered between the Xk gene and 14 other blood marker locations. This information allowed researchers to determine that the linkage is specific to PHI and Xk.
• The study also makes reference to another recent discovery—that of a linkage between Xk and a gene which produces the soluble malic enzyme (ME1). From these findings, they suggested the existence of an equine linkage group – LG IV. A linkage group is a set of genes on a chromosome which are inherited together.

Potential Homologous Linkage

• Finally, the researchers explore the possibility of a homologous linkage in pigs. A homologous linkage refers to genes that are linked in the same way in different species, suggesting a common evolutionary origin. Specifically, the study compares the newly-discovered linkage between PHI and Xk in horses, to a previously-known linkage in pigs, between PHI and a serum postalbumin (PO-2), indicating that these species might share a common evolutionary pathway.

It’s important to note though that the latter point was merely a discussion; a thorough investigation would be required to confirm this homologous linkage.