Invitrogen Corp. has agreed to pay $6.4 billion in cash to acquire Applera’s Applied Biosystems (AB) Group. AB develops DNA analysis devices for sequencing human genes. Earlier this year, the company announced it had sequenced an entire human genome for less than $60,000, down from the $3 billion spent on the Human Genome Project five years ago. Invitrogen makes a broad range of biochemicals and equipment used in government, academic and corporate medical research labs.     The two comp...