Marilyn Monk is a research scientist in the fields of molecular biology, early development and cancer. She is Emeritus Professor of Molecular Embryology at University College London, and Honorary Professor at Melbourne and Monash Universities

In 1983, her group discovered that the germline was derived from a sizeable pool of cells after implantation of the embryo in the uterus, thus ending August Weismann’s 1892 doctrine of the continuity of the germline in mammals. In 1984, her group showed that the expression of genes is programmed by modifications of the gene DNA. One of these epigenetic modifications is chemical attachment of a methyl group to one of the DNA bases. The pattern of this DNA methylation on the genes programmes a cell for specific function and behaviour – for example, to make a muscle or nerve cell, or a sperm or an egg cell.

In 1987, her group discovered an unexpected and important phenomenon in early development which she called ‘deprogramming’. This is the global erasure of the epigenetic programmes on the parental genes from the sperm and the egg. Deprogramming returns the embryonic cells to the tabula rasa (totipotent) state, capable of producing all the different cell types of the new individual. Marilyn has hypothesised that deprogramming may also be an initiating event in tumour formation and, subsequently, the development of cancer.

The hallmark of Marilyn’s bench research is the ‘micronisation’ of molecular techniques to the sensitivity of a single cell, in order to bring molecular biology to the very few cells available in early development. In another branch of her research, which has had far-reaching medical significance, she and Cathy Holding carried out the pioneering experiments which established the feasibility of preimplantation genetic diagnosis for couples at risk of having a baby with a serious genetic disease.