The cDNA project is an original project of Japan. To explain the difference between the Human Genome Project, first let's review about the structure of genomes.

DNA (genomes) are structured from exons and introns- the genetic part and the non-genetic part. Exon is the protein-coding DNA sequence of a gene, and takes up about 5% of the whole genome. All the rest are introns, the parts that interrupt exons. There are two parts to the intron- the regulator sequence and junk DNA.

The difference between the two projects. is that unlike the Human Genome Project, where all the DNA is decoded, the cDNA project only decodes the important genes- exon.

The Process of the cDNA project

The process begins by taking out a messenger RNA (mRNA) from a certain organ, and using a virus reversing transcriptase on to it, transforming it back to DNA. This human made DNA is called complementary DNA (cDNA). The information of cDNA are only of the parts read from that organ, so this process means the same thing as reading the instructions of proteins made by that particular organ. Unlike the Human Genome Project, the purpose of the cDNA project is to decode only the important parts of genes. So the absolute quantity is much less than of the Human Genome Project- only 1/50 to 1/100, compared with the work load of the Human Genome Project.
In this strategy though, only the instructions for specific parts of the body, such as the brain or feet can be made, and not of the whole genome. Another demerit of this project is that all the regulatory sequences in between the genes are completely ignored.

Below are some of the pros and cons of the Human Genome Project and the cDNA Project