Marker-Assisted Introgression Programs. Marker-assisted introgression has been the main approach for utilization of genetic markers in plant breeding and successes and limitations of these applications have been documented by Hospital etal. (2002). Because of longer generation intervals, lower reproductive rates, and greater rearing costs, introgression is only feasible
in livestock for genes of large effect. However, some examples of MAI in livestock are available. Hanset etal. (1995) reported on the successful introgression of the halothane normal allele into a Pie´train line that had a high frequency of the halothane-positive allele.
They used LD foreground selection on markers linked to the RYR locus. Yancovich et al. (1996) used marker assisted background selection to speed up the recovery of the broiler genome when introgressing the nakedneck gene from a rural low-BW breed into a commercial broiler line. Gootwine etal. (1998) reported on MAI of the Booroola gene (FecB) into dairy sheep breeds using
LD markers for foreground selection. In developing countries, programs for the introgression of disease resistance or tolerance genes are being considered for cattle (J. Gibson, ILRI, Nairobi, Kenya, personal communication).