as the embryo develops cells differentiate and become specialised for one function or a group of functions depending on the proteins that it synthesises.
scientists have discovered that different genes are expressed in different cells meaning cells have different functions.
scientists igor dawid and thomas sargent discovered this by extracting mRNA from differentiated and undifferentiated cells . they found that complientary DNA (cDNA) strands were produced for all the mRNA in differentiated cells using an enzyme called reverse transcriptase , which reverses transcription - making DNA from mRNA.
these cDNA srands were mixed with the mRNA from the undifferentiated cell. complimentary strands of cDNA and mRNA combined to produce double hybrids.
when these hybrids were separated out, there remained a range of cDNA stands that had not been hybridised - meaning the two cells were expressig some of the same genes but also some different genes.
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