Maize (Zea mays) Genome
The maize genome is almost as big in size as the human genome (~2.5 to 3.0 billion base pairs) and is highly repetitive with 65-80% of the genome consisting of retrotransposons, and another small fraction consisting of MITEs (miniature inverted transposable elements). Therefore, sequencing of this genome will be expensive and difficult. Nevertheless, a maize genome sequencing project is being initiated in USA. Since, maize genome differs from rice genome by as many as 15,000 rearrangements, it was believed that rice will be too distant to facilitate map based cloning in maize and other cereals like wheat, barley, sorghum, and oats.

This strategy would involve sequencing of only the gene-rich regions and not the sequencing of large proportion of the genome involving the repetitive region, thus reducing the work substantially. It was also agreed that the inbred B73 should be utilized for genome sequencing, since it is already being used for developing a BAC physical map and the ESTs.

In the year 2001, data on complete sequence of about 150 maize genes and several BAC clones and the shotgun sequencing of about 5000 random maize genomic clones were already available. More BACs were being sequenced during 2001-02 under various genome projects that were being funded at that time. A physical map involving BAC clones and the corresponding contigs and the anchor markers was estimated to be ready by spring (March-April) of 2003, which was considered essential for the maize genome sequencing project. The complete genome (only the gene rich regions) is estimated to be completed by the year 2005.