Developed by researchers at the Broad Institute of Harvard and MIT, Birdseed is an evolution of the RLMM genotype calling algorithm. It performs a multiple-chip analysis to estimate a signal intensity for each allele of each SNP, fitting probe-specific effects to increase precision (like the BRLMM-P algorithm developed for the Genome-Wide Human SNP Array 5.0). It then makes genotype calls by fitting a Gaussian mixture model in the two-dimensional A-signal vs. B-signal space, using SNP-specific models to improve accuracy.

References:
1. Rabbee, N., et al. A genotype calling algorithm for Affymetrix SNP arrays. Bioinformatics 22:7-12 (2006).

2. Affymetrix, Inc. BRLMM: An Improved Genotype Calling Method for the Mapping 500K Array Set.