To: MAURY MARKOWITZ Re: species Maury Here is another citation to add to your list of spec

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From: JEFF OTTO To: MAURY MARKOWITZ Re: species Maury - Here is another citation to add to your list of speciation events. This regards the speciation of laboratory strains of mice from the wildtype natural population from which they were originally taken. The full citation and abstract follow: Matsuda Y., Hirobe, T., and Chapman VM. 1991. Genetic basis of X-Y chromsome dissociation and male sterility in interspecific hybrids. Proceedings of the National Academy of Sciences. 88:4850-4 Abstract: A high frequency of X-Y chromosome dissociation (95%) was found at first meiotic metaphase (MI) in spermatocytes of interspecific hybrids between laboratory mice, C57BL/6J (BL/6) and Mus spretus, compared with an X-Y dissociation frequency of ony 3-5% in parental mice. The X-Y dissociation in F1 hybrids occurred before diakinesis rather than as a precocious spermatogeneic breakdown after MI, resulting in male sterility. All F1 males were sterile and approximately half of the backcross males from fertile F1 females corssed with either BL/6 or M. spretus males were sterile. Male sterility was highly correlated with X-Y dissociation in both backcrosses. All of the mice with hight X-Y dissociation were sterile and all of the males with low X-Y dissociation were fertile or subfertile. This correlation suggested that genetic divergence of the X-Y pairing region could contribute to the male sterile phenotype such that BL/6 X chromosome would not pair with the M. spretus Y chromosome. The segregation of species-type alleles of amelogenin (Amelb and Amels), a distal X chromosome locus adjacent to the X-Y pairing region, was followed in backcross males that were analyzed for X-Y dissociation and sterility (we have used Amel as the designation for the mouse amelgoenein locus; the current designation for this locus is Amg). A 95% concordance between Amelb with fertility and Amels with sterility was observed in backcrosses with BL/6, whereas the converse was observed in the backcross to M. spretus. These results imply that X-Y pairing plays an important role in male fertility and suggest that genetic divergence in X-Y pairingregions between Mus species can contribute to the reproductive barriers between species and the process of speciation.

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