A maximum likelihood approach is developed for estimating the recombination fraction in a segregating population (F2), between a marker gene and a locus affecting a quantitative trait as well as estimating the means and variances of the three genotypes of the quantitative trait. The experimental results from computer simulations show that even with experimental sizes of 500, estimates of the parameters can be obtained by aid of the codominant marker gene as long as the heritability of the quantitative trait in question is not less than 0.10. However at low heritabilities the variances of estimates are very large.