April 22  This is the first time in two years I have sat down to design. I gradually lose a sense of self, outside stuff fades and the inside takes over. The difference between starting Primitive Streak and any collection that has gone before is that beauty is the only objective, that and the life event I am trying to explain: the development of a human form.

April 28  If I had to pick a day when this project really started, it would be today. Spent four hours blasting information with Kate in the lab in Oxford. After three hours I couldn't take in any more: gastrulation, cell division, prophase, metaphase, teleophase, neuralation, primitive streak, fibroblast, blastocyst and more. Spent the evening deciding on what level to pitch the understanding of the project. We decided that if our children can begin to understand the basic phases of our embryonic origins as a result of the collection, then we will have got it about right. The key recurring problem of the project raises its head: how to represent the science fact without the wearer looking a total prat.

April 30  In London I can start to make sense of what I've seen down microscopes in Oxford. There are clearly moments in Kate's work that defy re-interpretation.

May 7  Working with my sister for the first time I am starting to notice and acknowledge things about her and, inadvertently and by comparison, about me too. With a knot in my stomach I have shown Kate the first draft of the collection. Her reaction will be vital to my confidence to carry on. Have I lost something? Misunderstood? Have I made symbolic that which must be blatantly clear? Most important of all, have I fallen into the trap of over simplifying the science and losing the fashion? As we go through the sketches I lay them out, from single cell through to the development of the thorax. Her eyes light up at giant and magnified sperm on the sleeves of a jacket, and the word "brilliant" pops out at the sequence of neurulation. The beginnings of what I wanted to achieve have started to emerge, there is some hope that my way of designing might be able to explain a scientific event in cloth and on a moving female body.

May 15  Suddenly there is not time to design. It's a change to be designing a collection that hasn't got some form of autobiographical root to it. It is by far the most electric project I've ever touched.

June 6  Kate arrived from Oxford at 7am, and we went straight into the collection. Both of us stare down again at the floor of sketches. Silences are full of negotiation, a process of teaching, learning, translation and agreed "artistic" representation. From Kate to me and back again. What art can really do for science may be misguided, for art does not have to be exacting. Its purpose, then, in a project like this may only be to raise awareness, to act as a magnet to those who might not normally go near it. Not so much explanation as an attempt at communication.

June 14  I feel at the moment that I am less a designer and more an illustrator. Kate feels I have to be satisfied with the collection from a fashion point of view and that if I am not then we will have lost the power of communication - in which case the collection stinks, it's a piece of self-conscious stodgy shit. I want to start all over again.

July 6  feel out of control, I'm not designing, I'm taking visual dictation.

Kate's Story

April 28  Helen's first visit to the lab, and our first day on our Wellcome Trust Sci/Art project, Primitive Streak. We aim to elucidate ten key events in embryonic life, beginning with fertilisation and progressing as far as the recognisable human form - two arms, two legs, a head, a face - through Helen's medium, fashion design. We talked and drew developing embryos for three hours. I tried to describe why these events were important. It was exhausting. Too much to take in for Helen. Hard for me to translate everything into layman's terms. It is surprising, discovering this other Helen, who wants to know everything in such detail. It is great to be working with someone so committed and full of ideas.

April 29  Helen had her first experience of living chick embryos (which at early stages of development look very like the human embryo). I showed her two stages: a primitive streak stage embryo (12 hours' incubation) and a later one in which the simple heart tube had formed (30 hours' incubation). She was amazed by their translucence and colours and by their depth. We discussed why the primitive streak is so important, why we should use it as a focus of the collection: it is the site of gastrulation, the process by which the crucial third layer of the embryo is generated, and it is the source of many of the tissues of the body. I think I got across the fundaMental idea that the embryo consists of cells that are constantly dividing and moving to generate its overall form. She seemed finally amazed, like all developmental biologists, by the precision with which cells become the right type (nerve or skin or muscle, etc.) in the right place.

April 30  Met up with Helen for an interview in London. The project seemed suddenly to be rising from the paper and acquiring its own identity.

May 5  Woke up worrying about the early cell division designs. We are going to represent these first divisions of the fertilised egg as a series of spheres within spheres suspended in a hoop out of the side of the dress. Will they look cancerous? How three-dimensional should they be? Is Helen happy with them? Perhaps we need to develop a style or look for the whole collection.

May 17  Cambridge. Visiting our friends Maggie and Dennis Bray. Dennis is an eminent cell biologist and one of the authors of The Molecular Biology of the Cell, an essential text in our field. He also has an artistic eye and is therefore an ideal person with whom to discuss Helen's latest designs. To begin with I think he was surprised by what we were attempting to do, but quickly saw how some of the designs were working. In the end he was more enthusiastic than me: "If anyone comes away with 'primitive streak' tripping off their tongues it will have been worth it..."

May 20  I showed the collection to a number of colleagues. Professor Gillian Morriss-Kay (an embryologist). Dr Helen Skaer (a developmental biologist) and Dr Marco Lee (a clinician). They were all enthusiastic about the idea and they were all put off by the same things - by incidentals that they couldn't place, such as earrings or hairstyles. They commented very much on specific details like this. Perhaps because they were shy of commenting on the wider concept? They each focused on a few drawings that they liked, for aesthetic reasons, I think, or because they were familiar images. They seemed genuinely embarrassed by the boldness of other designs, such as the sperm strapped round the model's thigh with a symbolic coil of mitochondria. Helen and I drew the changing shapes of the developing heart. This kind of interaction is more demanding than I expected. I had thought that this part would be easy, that it would be a relief to be free from the exacting process of science, which is full of checking and refining, but in fact it is harder. If we are to get it right it has to be exact in both an artistic and scientific sense.

August 12  The most wonderful part of the day was seeing how Helen's sketched designs have translated into cloth. The black and red implantation dress is ready, all but the hem. It works so well as a dress. I am amazed.

August 16  Surprised and dismayed to learn from Helen that at times she feels she has lost touch with the design process and has been taking "visual dictation". With hindsight we should have spent longer at the early stages, building up Helen's confidence with the sequence of development and with the terminology. I think this is a problem with communicating science; it is believed to be a series of unquestionable facts and non-scientists are afraid to explore it. I had hoped to be a conduit through which she could gain access to a new world.

August 17  We have reached a real low. I sense Helen is emotionally and physically exhausted, but cannot give up now. I feel a parent-like responsibility for her in one mood and amazed by her in another. Helen's world is all about vulnerability, while science is less personal, buffered by objectivity and better experiments to come. Perhaps that's why I went into it; science is less painful and its substance more tangible. Maybe the project simply doesn't work because it is phoney, pretentious rubbish - or will it bridge a gap?

August 24  Helen has just faxed through the latest version of the heart development sequence. It looks fantastic. She has given the final heart form, sitting on its diaphragm, a set of tail feathers. The whole thing looks like a robin with a read breast. The feathers perfectly balance the rather monstrous heart in front. Helen has made the heart her own.

September 4  A smile from Helen as we part in the Tube beneath Baker Street quashes my anxieties. She has found so many ways of expressing herself through the project that it must surely work - at least in terms of fashion.

Helen’s Story

August 12  Kate came down to look at the collection's progress. She seemed interested in my work environment, and in a joint interview made her first-ever verbal observation of my little world. She seemed pleasantly surprised at the similarities between how a lab is run and a workroom. In the past I imagine that her perceptions of my professional life have been based on the image the fashion industry can't help but perpetuate - all glamour, kisses and hysterics. What she saw was that there is order, precision, trust, a shared vision and a lot of hard work.

September 11  A photo shoot, six months of experimentation come together. This is the first opportunity I have had to stand back and see the work as others might. It's a good time to consider whether you've pulled it off or not, as it's too late to do anything about it if you haven't. The model is so important. She can embody the first thought you had, with Lana, she began to look uncannily like my first sketches all those months ago. The shoot also marks the time when you have to let go, when the judgement and criticism starts on whether science and art, or in this case fashion, have anything valid to say to each other. I think we are still in the process of finding out: we haven't finished with each other yet.