Marker-assisted selection is the most widely used application of DNA markers. Once traits have been mapped and a closely linked marker has been found, it is possible to screen large numbers of samples for rapid identification of progeny that carry desirable characteristics.

Example: Resistant & susceptible lines in tomato

A marker link to the resistance gene scores at different positions for resistant and susceptible lines.

Using markers for trait selection has numerous advantages when compared to conventional plant breeding:

• Speed – DNA can be extracted from tissue from the first leaves or the cotyledons of a plant. Trait information can be discovered with markers prior to pollination allowing more informed crosses to be made.
• Consistency – Markers remove the impact of environmental variation that often complicates phenotypic evaluation.
• Biosafety – Using markers in screening for disease resistance means not having to introduce the pathogen into breeding populations. Particularly for livestock breeding this delivers a very important level of biosafety.
• Efficiency – Screening progeny early in the process allows a breeder to drop “also-rans” from the program more quickly. Most breeding programs that use markers still evaluate the same number of plants in the field however the level of genetic quality is vastly increased because of the early-stage screening that has been carried.
• Complex traits – Most multigenic traits are very difficult to manage through conventional plant breeding. The statistical chance of getting the required allele at each of a number of loci is very low. Markers allow you to skew the odds in your favour.

In most major crops, various linked markers exist to screen key traits. However if the trait has not been mapped to a marker, it is possible for DNA LandMarks to carry out the research necessary to find linked markers for your trait of interest (see Marker Development and Mapping).