The heritability of phenotypes are normally defined by means of twin research. However, twin researches are expensive and time-consuming, and the number of twins required in the researches is limited. Twin researches have also received criticism, because they are based on the assumption that monozygotic twins are identical, but new research shows that they are not entirely identical. Even bigger criticism is levelled at the assumption that the effect of the common environment of monozygotic twins is insignificant, which leads to bigger heritability estimates. There is considerable evidence that the common environment is not the same for the two type of twins.

In the future new more effective genotyping technologies enable the collection of genotype data from a larger group of people. Determining phenotype heritability of individuals just by using genotype data would provide an easier way to estimate the risks of different diseases, such as cardiovascular diseases, and prevention of these diseases would be more effective. In 2005 just cardiovascular diseases caused 17 million deaths worldwide.

This final year project studied the association of phenotype and genotype, and heritability of these phenotypes. The aim of this project was to determine the associations and heritabilities with simple association analyses just by using large genotype datasets.

Analyses were made with two entirely Finnish study cohorts containing nearly 7500 people, and the phenotypes were common risk factors of cardiovascular diseases and people height. Associations were studied by means of XY scatter diagrams where identity by descent difference was in X-axis and phenotype difference in Y-axis, and heritabilities were determined by linear regression using principal components derived from genotype data by principal component analysis.

Analyses did not reveal any significant genome-wide associations between phenotype difference and genotype difference using genome data. Principal components could not be used to determine the heritability of the phenotypes. The analyses used in this project cannot be used as such in heritability studies. In new studies analyses should be made by methods derived from these analyses.