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- Author: B. M. N. Wallace x
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Female common shrews in their first pregnancy were collected near Oxford (UK) from the hybrid zone between the Oxford and Hermitage races. These races differ by Robertsonian chromosomal rearrangements and both Robertsonian heterozygotes and homozygotes are found in the zone. The three homozygotes examined in this study had significantly more oocytes than the six heterozygotes. Among the heterozygotes, the number of oocytes tended to be lower in more severely heterozygous individuals; one double heterozygote was particularly depleted. Although there were, on average, 41% fewer primordial follicles in the ovaries of the heterozygotes than those of the homozygotes, there was no significant difference in the numbers of growing follicles between the karyotypic classes. These data suggest that Robertsonian heterozygotes may have a shorter reproductive lifespan than do homozygotes, but the numbers of follicles being recruited for ovulation at a particular instance during the fertile period does not appear to differ between homozygotes and heterozygotes. Morphological differences between the follicles of homozygotes and heterozygotes were not detected. Only 0.12% of healthy growing follicles were biovular.
