The following tetrads were produced by a cross of a Neurospora strain that had w

Question

The following tetrads were produced by a cross of a Neurospora strain that had white spores (w) and a nutritional requirement for the amino acid arginine (arg) with a strain that had dark spores and no arginine requirement:

Spore                                    Tetrads                                

Pairs      1              2              3              4              5              6

1

Explanation / Answer

http://plantpath.ifas.ufl.edu/classes/pmcb5065/dgl3.htm This explains all of this very well and gives examples beter than I can. I beleive you labled the 1st and 2nd segregation patterns correctly. but I think you have the tetrad typing (PD/NPD/TT) wrong. PD = parental ditype and is the result of no crossing over TT = tetratype and is the result of a single cross over event NDP = nonparental ditype and is the result of 2 cross overs that involve all 4 chromatid (4 strand cross over) So tetrad 1 would be PD and tetrad 5 would be NPD so, recombinant frequency would be (1/2TT + 3 NPD)/total tetrads however this underestimates the total number of cross over in double cross over events involving all 4 chromatid, so the equation is adjusted as, (1/2TT + 3 NPD)/total tetrads (20.5 + 3)/100 = 0.235 note the genes are linked if PD > TT > NPD since yours is 58 > 41 > 1 Cut an paste the link i put at the top, if my explanation didn't help that should! Good luck :)

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