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The two chromosomal male-sterility mutants referred to as Pugsley's male-sterile and the Probus male-sterile fail to complement one another. Partial monosomic analysis revealed that both mutants are located on chromosome 4A. A strong homoeoallelic 'echo' was received from chromosome 4B with the Probus mutant, mslb, but not with Pugsley's mutant, msla.
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C. J. Driscoll (1975) studied this question.
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