Abstract
1. If data on tetratype frequencies refer to unlinked pairs of loci, even though the loci are not necessarily all unlinked, then centromeres can be mapped if the data include an odd-numbered closed set (or cycle) of frequencies (e.g. frequencies known fora andb,b andc, c anda, wherea,b andc are mutant genes). Formulae are given for calculating second-division segregation frequencies and their standard errors from such odd-numbered cycles. 2. If unlinked tetratype data include only an even-numbered cycle (e.g. data fora andb,b andc,c andd,d anda, whered is a fourth gene), then second-division segregation frequencies cannot be calculated, but a relationship exists between the tetratype frequencies. It can be used to test the homogeneity of such data. 3. If one of the tetratype frequencies refers to a linked pair of loci, centromeres can be mapped provided the frequencies form a cycle of at least three values, a.nd provided at least one of the linked genes is situated near to the centromere of its chromosome. Formulae are given for calculating second-division segregation frequencies from cycles of three and four loci, when one pair of loci show linkage.
Published Version
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