Abstract
Map lengths are useful for knowing the relative sizes of chromosomes and for making expectations of gametic frequencies when hybrids segregate for several factors. However, no method of arriving at them is available so far. Recombination fractions larger than about 10 crossover units, being nonadditive, are unsuitable for denoting map distances. Kosambi (1944) proposes a formula, 2 y = tanh (2 x), for estimating map length x corresponding to the recombination fraction, y. Being empirical, the formula requires testing for applicability. The article represents such a test made with Jodon''s (1940) data on the chromosome containing the "Virescent" mutation in rice. This is the 4th test of the formula, since it was proposed, in which it has been found to be applicable.

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