Map distances based on recombination rates between distant g

Map distances based on recombination rates between distant genes often underestimate the true physical distances between genes because some multiple crossovers go undetected. some genes are lethal. interference increases as the distance between genes increases. testcross results can\'t be used to map genes that are far apart. rates of crossing over are not uniform.

Solution

Map distance based on recombination rates between distant genes often underestimate the true physical distances between genes because rates of crossing over are not uniform. There are more regions of recombination called recombination hotspots present on the chromosomes which are more likely to be involved in cross over, therefore rates of crossing over are not uniform. This shows that genetic map distance does not necessarily tells the exact physical distance between genes. We cannot deny the fact that recombination frequency can be obtained only till 50% so 50 cM distance can be anticipated but if the recombination is more than 50% then distances can\'t be measured (e.g distance can\'t be 55cM etc).