Chromosome read depth analysis/Reads were mapped to the appropriate reference genomes using MAQ (Li et al. 2008) version 0.7.1 (http://maq.sourceforge.net/), under the guidance of a custom Perl script. Read sets were parsed into smaller paired sets of 2.5 3 106 reads or less and converted into binary format. The number of bases mapping to each position in each chromosome was recorded and used to determine the total number of read bases mapping to each chromosome and the median read depth for each chromosome. Observing that a majority of chromosomes displayed similar median read depths, and interpreting this as a nominal ‘‘ploidy’’ for the cells, a within genome normalization was performed by setting the average of the read depth of the four longest disomic chromosomes to 2. The read depth for each chromosome was subsequently normalized to this value.