Dozens of twins have been invited to a Scottish university to participate in a special event aimed at furthering medical research.
Researchers say they can learn a lot from studying twins
The gathering at Aberdeen University was arranged as part of an ongoing research project by the Twin Research and Genetic Epidemiology Unit.
Experts said useful data can be gleaned from tests including blood samples and height and weight measurements.
The university and Rowett Research Institute have also been participating.
About 35 pairs of twins were invited to the event, organised by the research unit at Guy's and St Thomas' NHS Foundation Trust in London.
Data from various Twin Days has been gathered for the ongoing research programme TwinsUK, funded by the Wellcome Trust.
During the events, blood samples and facial photographs have been taken and height, weight and grip strength measurements and blood pressure recorded.
Twins also complete questionnaires with results added to data compiled by the unit on 10,000 twins in the UK. This is then used for health research projects.
The information will also be added to research at the university and Rowett Institute on blood diseases and on genetic and dietary factors which influence cardiovascular disease.
Professor Tim Spector, director of the Twin Research and Genetic Epidemiology Unit, said: "We are collecting data on all 10,000 twins registered on our database. We aim to establish a biobank of twin DNA which will be vital in studying many chronic diseases of ageing.
"Twins are unique natural experiments. The genes of identical twins are the same so comparing them with non-identical twins, who share only half their genes, allows us to separate nature from nurture.
"It also allows us to pinpoint the causative genes and to accurately measure the effects of our environment, for example diet."
Dr Geraldine McNeill, from the university's Department of Environmental and Occupational Medicine, said: "Twins who take part in this kind of research are making a valuable contribution to our knowledge of how genes and other factors influence health."