Centre for Genetic Improvement of Livestock
Update 2000

Right On The Mark
Molecular Markers Help Map The Pig Genome
by
Jenny Tye

 

 


Profs. Zhihua Jiang and John Gibson are working with researchers in Scotland to compile genetic information that will allow them to quickly and efficiently pinpoint pigs that are most likely to succeed in genetic evaluations


Quickly and efficiently pinpointing animals most likely to succeed in genetic evaluation is crucial in today's highly competitive swine breeding business. And that's part of the reason Profs. John Gibson and Zhihua Jiang, Centre for Genetic Improvement of Livestock, are working with researchers from the Roslin Institute, Scotland to detect genes called quantitative trait loci (QTL). These genes cause variation in swine and can have economically important effects on traits such as reproduction.

Ultimately, locating QTLs will help pig breeders quickly select those progeny that are most likely to pass superior reproductive ability to their offspring. This project is part of a larger effort aimed to help Canadian swine breeding programs stay competitive by developing a solid and viable Canadian research program in pig genome mapping.

Right now, the researchers are tracking inheritance patterns of QTLs that affect litter size in crosses of Chinese Meishan pigs -- famous for large litter sizes -- and European Large White pigs, popular in North America for sow productivity and carcass traits. Litter size is one of the most difficult and expensive traits to improve in traditional swine breeding programs because reproduction can only be measured in sexually mature females.

Using Powerful Genetic Tools

To detect QTLs, the researchers are using powerful genetic tools called molecular markers. Each marker is a landmark at a specific point on a given swine chromosome and can be associated with genes of economically valuable function. When researchers follow the inheritance of a particular marker from parent to offspring, they also follow the inheritance of a particular region of a chromosome. Genetic markers provide an accurate way to learn about an animal's genetic make up.

Molecular genetic markers are divided into two groups: anonymous markers and candidate gene markers. Anonymous markers are not part of known genes and do not control sequences of known genes. However, when an animal inherits a genetic marker from its parents, it also inherits a large region of DNA on either side of the marker. When researchers follow the inheritance of these anonymous markers from parent to offspring and compare this information to the genetic value of each sow, they can determine which DNA segments have useful effects on reproduction.

Candidate gene markers are used similarly to anonymous markers. But they're more targeted and can detect variation in swine genes of known or inferred function, related to reproduction.

Microsatellite Markers

For this genome mapping project, researchers at the Roslin Institute collected information from their resource swine herd using microsatellite markers, the most widely used class of anonymous markers used in genetic research today. The CGIL researchers collected information from the same pigs using a newer and less commonly used type of anonymous marker, called amplified fragment length polymorphisms (AFLPs), as well as candidate gene markers. Gibson, Jiang and their colleagues in Scotland are now compiling and analyzing the data collected during the three marker studies.

Each marker type complements the other because they differ in the amount, type and quality of information provided. In this way, the researchers ensure they gather the most comprehensive QTL data possible.

Using different marker types has other advantages, too. As part of this pig genome project, the researchers are comparing the performance of the two anonymous marker types, AFLP and microsatellites. AFLP are faster and less expensive to use than microsatellites, but AFLP can be difficult to score. This pig genome project is the perfect opportunity to scientifically explore the potential for more AFLP use in future genome mapping projects.

Data collection for the first part of this study is now complete, but data analysis is still underway. The CGIL researchers will soon continue and then test their pig genome work with another company called Genex, which has a commercial Meshian x Large White herd in Saskatchewan.

This research is sponsored by Ontario Pork, Ontario Swine Improvement, the Natural Sciences and Engineering Research Council and the Ontario Ministry of Agriculture, Food and Rural Affairs.