Son-sire regression based heritability estimates of chiasma frequency, using T70H mouse translocation heterozygotes, and the relation between univalence, chiasma frequency and sperm production

Abstract

SUMMARYT( 1; 13) 7011/ + translocation heretozygous mice were used for assessing heritability values for chiasma frequencies and the epididymal sperm count. The chiasma frequency estimates were based on 15 son-sire pairs, the translocation hcterozygotes being maintained in a Swiss random-bred genetic background. The chiasma frequencies were scored separately for the T7OH/ + derived multivalent, specific pairing segments within the multivalent and the remaining bivalents. Chiasma counts within these specified parts of the genome were positively correlated. The heritability estimates, significantly greater than zero, ranged from 078-098, depending on the chromosome segments included. These results indicate a strong genetic control on a cellular basis for the formation of chiasmata in the mouse. Despite significantly positive correlations and regressions between the various chiasma frequencies and the sperm count (for which 29 pairs of observations were available), no significant heritability estimate for the sperm count was obtained. The relation between the chiasma frequency and the sperm count was weakest when the chiasma count was confined to a region of the translocation-caused multivalent in which the absence of a chiasma almost always resulted in the production of an univalent. This indicates that in the translocation heterozygotes used, the overall chiasma frequency has a greater predictive value for the sperm count than autosomal univalence alone.

Proximal chiasma localization within an interstitial chromosome segment, a likely correlate of adjacent-2 segregation of translocation causing multivalents in the mouse.

“…This holds true for both the CIV and CIII+I configurations. As found earlier (5), the fraction of the cells containing two chiasmata in segment It drops when meiosis proceeds. When the 16.4% chiasma positions in this segment are compared between cells with one or two chiasma(ta) ( Table 3), a difference is apparent.…”

Proximal Chiasma Localization within an Interstitial Chromosome Segment, a Likely Correlate of Adjacent-2 Segregation of Translocation Causing Multivalents in the Mouse

“…When diakinesis proceeds to metaphase I, the chiasma in segment 13t has a tendency to terminalize. This causes an increase in the fraction of CIII+I configurations in the spiralization classes 2 (middiakinesis) and 3 (late diakinesis and metaphase I), confirming results published earlier (3,5). The data presented here are given in Table 1.…”

Interference relationships in grasshopper reciprocal translocation heterozygotes

“…Negative interference between specific regions of interchanges has been also reported (Sybenga, 1975;de Boer and van der Hoeven, 1977) and this has been subsequently tested in a number of different translocations in rye (Sybenga and Mastenbroek, 1980) and wheat (Fominaya and Jouve, 1986). According to Sybenga's model (Sybenga, 1970;1975) there should be negative interference between segments located in opposite arms of the pachytene cross and positive interference between adjacent ones.…”