# Homework Help: Drawing a genetic map (recombination)

1. Feb 23, 2006

### confusedbyphysics

We discovered that in the fungus Sordaria fimicola, a gene caused the fungus to produce normal black or mutant tan colored ascospores. Observations of crosses between normal and mutant fungi showed that 56% of the asci produced by these hybrid fungi are recombinant. This translated to a 28% recombination frequency in the individual spores, which indicates that this gene is 28 cM (map units) form the centromere.

Now suppose that a new mutant allele has been discovered in a gene that controls spore size, with alleles that produce normal large or mutant small scospores. Expirements reveal that this gene locus has a recombination rate of 19%, which corresponds to 45 cM from the centromere.

Additionally experiments done with crosses between spore color mutants and spore size mutants find a recombination rate of 44% between the gene for spore color and the gene for spore size.

Draw a map of the chromose these two genes are found on, including the centromere, and both genes. Draw the correct positions of the genes relative to each other and to the centromere, and indicate teh distance between each.

-----------

I understand the example in the book but I do not see how this adds up. If the recombination rate between the two genes is 44%, that means there is 44 cM between them.

But if you put both genes on the same side of the centromere (28 cM and 45 cM), that leaves only 17 cM between them, not 44. If one gene is on one side of the centromere and the other is on the other side that would be 28+45=73 cM between them, again not 44.

what am I doing wrong? thanks for any help!!

Last edited: Feb 23, 2006