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Abstract: The genome-wide recombination rate $RR$ of a species is often described byone parameter, the ratio between total genetic map length $G$ and physicalmap length $P$, measured in centiMorgans per Megabase cM-Mb. The value ofthis parameter varies greatly between species, but the cause for thesedifferences is not entirely clear. A constraining factor of overall $RR$ in aspecies, which may cause increased $RR$ for smaller chromosomes, is therequirement of at least one chiasma per chromosome or chromosome-arm permeiosis. In the present study, we quantify the relative excess of recombinationevents on smaller chromosomes by a linear regression model, which relates thegenetic length of chromosomes to their physical length. We find for severalspecies that the two-parameter regression, $G= G 0 + k \cdot P$ provides abetter characterization of the relationship between genetic and physical maplength than the one-parameter regression that runs through the origin. Anon-zero intercept $G 0$ indicates a relative excess of recombination onsmaller chromosomes in a genome. Given $G 0$, the parameter $k$ predicts theincrease of genetic map length over the increase of physical map length. Theobserved values of $G 0$ have a similar magnitude for diverse species, whereas$k$ varies by two orders of magnitude. The implications of this strategy forthe genetic maps of human, mouse, rat, chicken, honeybee, worm and yeast arediscussed.

Author: Wentian Li, Jan Freudenberg


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