Figure 1

Likelihood plateau under high and low marker spacing. When there is not sufficient information, the likelihood will not peak at the location of the QTL, but may have a plateau centered at the QTL location. With the higher marker spacing, four markers are on the plateau of the likelihood, of which two are inside bracket B. Thus the QTL has probability 0.5 to be mapped inside bracket B. With lower marker spacing, ten markers are on the plateau, of which six are outside and four are inside bracket B. Thus the QTL has a higher probability to be mapped outside than inside bracket B, which results in lower precision. However, when there is sufficient information due to a larger number of observations or higher QTL variance, the likelihood will be more peaked. Thus there is less probability that the QTL will be mapped outside of bracket B, resulting in a higher precision with a decrease in marker spacing.