Abstract: The present invention is directed to a new method for genotype determination at a specific gene locus of an individual or a fetus comprising (i) amplifying a first sequence of said gene locus and a second sequence of a second reference gene locus from DNA originating from a sample containing biological material of said individual or fetus (ii) Monitoring both amplifications preferably in real time and determining the amount of amplification products after each cycle, and (iii) Calculating the ratio between the amount of DNA from the first gene locus and the amount of DNA from the second gene locus. The new method is useful for a variety of applications, especially for detection of chromosomal abnormalities in fetal cells.