Adding more sample
We have 50 human whole genome data (12x) from the same population and we have already used GATK to call variants and followed the best practice for population level calling. We have then sequenced 20 more individual (12x) from the same population. For the population level variant calling do we have to put all the BAM files (50+20) together and then call the variants(in UnifiedGenotyper) ? Or we can somehow use the VCF file which was created from the previous 50 individual and use them as training set and call the variant for the new 20 individuals?