Experiments were performed to investigate the changes of lumbar vertebral numbers caused by reciprocal crosses between two inbred strains of mice which have different lumbar vertebral numbers and to analyse the influence of two different feeding conditions upon such changes. As‘interfrontal bones’ were found in the same materials, the distribution of these bones among the two strains and their hybrids F
1 was also examined.
The animals used in this study were two inbred strains of mice, dd, rr and their reciprocal hybrids F
l. They were divided soon after their birth into two groups namely, with high and low protein feeding conditions thus have been fed during 60 days.
1) The lumbar vertebral numbers of dd, rr were predominantly 6 in the former and 5 in the latter. Their numbers of the hybrids F
1 had a tendency of resembling those of rr.
2) As for the lumbar vertebral numbers of dd, rr and of their hybrids F
1, there was little difference in the two feeding conditions.
3) The investigation of the distribution of‘interfrontal bones’ showed that the ratio of these bones to those of normal dd was the same as that of rr, and the ratio in hybrids F
1 was slightly higher than those in inbreds dd, rr.
4) No changes were found in the distribution of‘interfrontal bones’between two studied groups with different feeding conditions.
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