Chiasma distributions and chromosome segregation in male and female translocation heterozygous mice analysed using FISH |
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Authors: | Charles Tease |
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Institution: | (1) Mammalian Genetics Unit, Medical Research Council, Harwell, Didcot, Oxfordshire OX11 0RD, UK, ML |
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Abstract: | Two factors postulated to influence the meiotic behaviour of reciprocal translocations were investigated. Firstly, variation
in the length of translocated and non-translocated segments was studied in male mice using four different rearrangements involving
chromosomes 2 and 4. Secondly, sex-related effects were analysed through comparison of the meiotic behaviour of two translocations
in male and female germ cells. In the first part of the study, primary and secondary spermatocytes of male mice carrying a
translocation T(2;4)1Ca, T(2;4)13H, T(2;4)1Sn, or T(2;4)1Go] were screened. Each rearrangement had different proportions
of cells with ring and chain quadrivalents at metaphase I; the T(2;4)1Sn heterozygote also had a high rate (45%) of translocation
bivalents. In general, the translocations had elevated chiasma frequencies in the rearranged chromosomes compared with structurally
normal chromosomes 2 and 4, although the extent of the effect varied. Each rearrangement produced a different array of segregation
products at metaphase II, reflecting their contrasting frequencies of multivalent configurations at metaphase I. Comparison
of chromosome behaviour at metaphase I and II suggested that certain configurations tended to adopt particular orientations.
However, it was also clear that such correlations were imprecise and that other factors, possibly the exact positions of chiasmata,
also played a role in multivalent orientation. Two rearrangements, T(2;4)1Go and T(7;16)67H, were analysed in female mice.
The frequencies of the various multivalent types at metaphase I differed from those in male carriers of these rearrangements
owing to an increased chiasma frequency in oocytes in some of the pairing segments. Not surprisingly, the segregation products
seen in metaphase II cells showed some differences from the pattern recorded in male germ cells. For T(2;4)1Go, the sex-related
difference in segregation patterns resulted in a diminished expectation of genetically imbalanced gametes, although this was
not the case for T(7;16)67H.
Received: 6 June 1998 / Accepted: 9 October 1998 |
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