But according to Professor Robin Lovell-Badge, of the National Institute for Medical Research in Mill Hill London, people should not worry unduly over the germ-line alterations.
First, the discovery of rare, high penetrance germ-line mutations of BRCA1 and BRCA2 identified a small subset of women with a very high life-time risk of breast and ovarian cancer.
But the cells from the first divisions retain the ability to form entire new embryos themselves. (This is how identical twins form.) Germ-line manipulation would require taking some of these early-embryonic cells apart in order to discover what the genetic lottery had delivered to them (a process that would destroy the cells in question).