Paternal Heterosis for Reproductive Traits in Mice

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  • マウスの繁殖能力に発現する父性ヘテローシス
  • マウス ノ ハンショク ノウリョク ニ ハツゲンスル フセイ ヘテローシス

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Abstract

Male mice of inbred strains, C57BL/6 and BALB/c, their first cross (F1), first backcross, F1×BALB/c(BC1), and second backcross, BC1×C57 BL/6 (BC2), were mated with ICR females in order to estimate the paternal heterosis for reproductive traits. BC1 and BC2 were 50 and 75% heterozygous, respectively, relative to F1 (100% heterozygous). The paternal heterosis estimates regarding delivery rate, days of exposure to a male to parturition, litter size and litter weight were 8-19%, 5-8%, 13-15% and 10-16%, respectively. Those estimates were statistically significant except for delivery rates of BC1 and BC2. There was, however, no relationship between the heterosis and heterozygosity of the crosses. The in vitro fertilizing capacities of spermatozoa recovered from cauda epididymidis of the same two inbred strains and their reciprocal F1 crosses were tested to detect the mechanism of the paternal heterosis using ICR eggs. The fertilization rates (number of 2-cell embryos per total number of eggs) were 92 and 87% for reciprocal F1 crosses, respectively, and 75 and 72% for C57 BL/6 and BALB/c, respectively. The higher fertilizing rates of the crosses suggests that the vigor of the spermatozoa of the hybrid animals is an important factor in the paternal heterosis of litter size.

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