BAC end sequencing and methyl-filtration libraries

BAC end sequencing: although BAC clones are too long (typically around 100kb) to sequence in their entirety, each clone can be sequenced about 500-1,000bp in from both ends. Only a fraction of these sequences can be expected to represent fragments of, or complete genes.

Methyl filtration or methyl-restriction libraries: these libraries are based on the tendency (not always correct!) of the bases in genic sequences to be less heavily methylated than those in non-genic regions. Thus highly-methylated regions of the genome can be selected against by digesting the DNA with methylation-sensitive restriction enzymes, leaving mainly gene-rich regions of the genome to be sequenced.