Meiotic metaphase-I Research Articles

Genome analysis of intergeneric hybrids of apomictic and sexual Australian Elymus species with wheat, barley and rye: implication for the transfer of apomixis to cereals

Four hybrids were obtained between three Australian Elymus taxa and three cereal grains: wheat, rye, and barley. Mean meiotic metaphase-I configurations were 41.14 I, 0.42 rod II, 0.003 ring II, and 0.01 III for E. scabrus var 'plurinervis' x Triticum aestivum (1 hybrid plant), 22.27 I, 2.63 rod II, 0.06 ring II, and 0.12 III for E. scabrus var 'scabrus' x Secale cereale (4 hybrid plants), and 26.65 I, 0.66 rod II, 0.00 ring II, and 0.01 III for E. scabrus var 'plurinervis' x Hordeum vulgare (13 hybrid plants). The I genome of barley also paired very little in a BIII hybrid of apomictic E. rectisetus x H. vulgare (2 hybrid plants). Megasporogenesis in this BIII hybrid was at least facultatively apomeiotic, with the same sort of nuclear elongation, apomeiotic division, and dyad formation seen previously in E. rectisetus itself. All four hybrid combinations were sterile. While spike morphology in the E. scabrus x T. aestivum and E. scabrus x H. vulgare hybrids were intermediate to their parents, E. scabrus x S. cereale and E. rectisetus x H. vulgare looked like their maternal parents.

Hypervariable minisatellite regions are sites for crossing-over at meiosis in man.

In situ hybridization to human meiotic metaphase I (MI) preparations, using the labeled minisatellite core sequence lambda 33.15, showed clustering of autoradiographic grains principally at or around chiasmata, autosomal sites where crossing-over had occurred. For the XY bivalent, the pairing region formed between the terminal regions of the two short arms (Xpter Ypter), was also a principal site of labeling; in addition, the terminal region of the X long arm (Xqter) was labeled. Control experiments using a member of the human Alu family of dispersed repeated DNA sequences showed a much more randomized grain distribution, with clustering over chiasmata being far less obvious. The data provide support for the suggestion that polymorphic minisatellite regions within the human genome might play a significant role in pairing and/or recombination.

4倍性ワケギと複2倍体 (シャロット×ネギ) との雑種の核型, 減数分裂及び稔性

In the somatic chromosome complement of the hybrid between the tetraploid Allium wakegi and the amphidiploid (A. ascalonicum×A. fistulosum) 16 pairs of chromosomescould be morphologically distinguished, and the karyotype was expressed by the following formula: K (2n) =2(14V+J(t)1+JT2). At meiotic metaphase-I in the pollen mother cells of the hybrid 16 bivalents were regularly formed. At metaphase of pollen grain mitosis most of the pollen grains possessed the chromosome complements (K (n) =14V+J(t)1+JT2) equivalent to the exact half of the somatic chromosome complement of thehybrid. Moreover, the hybrid was pollen fertile and had a good seed set. Therefore, it became clear that A. wakegi has the same genome constitution as that of the hybrid between A. ascalonicum and A. fistulosum. This indicates incontestably that A. wakegi is the synthetic species of these two species.

A reciprocal translocation induced in an oocyte and affecting fertility in male mice

The reciprocal translocation <i>T(5;12)31H, </i>induced by irradiation of oocytes, causes sterility in most heterozygous male carriers, a tenfold reduction in mean sperm count, and a high frequency of abnormal sperm. Chromosome breakpoints are in bands 5B and 12F1, leading to a long (12<sup>5</sup>) and a short (5<sup>12</sup>) marker chromosome. Ninety five percent of germ cells showed chain quadrivalents or trivalents at meiotic metaphase I (MI). The order of loci on chromosome 5 is centromere—<i>T31H</i>—<i>Rw</i>—<i>go </i>with a recombination frequency of 31 + 7% between <i>T31H </i>and <i>Rw</i>. No linkage was found between <i>T31H </i>and linkage group XVI genes previously assigned to chromosome 12; it was concluded that they are located elsewhere. Viable tertiary monosomic and trisomic young (lacking the 5<sup>12</sup> region or with it in excess) were generated with post-natal frequencies of 4.5% and 14.6%, respectively, from outcrosses of heterozygous females. A deficiency of monosomics was also found in 11½ to 14½ day foetuses, when abnormal phenotypes or severe retardation produced by other unbalanced karyotypes were found. There was also a marked deficiency of monosomic offspring from outcrossed monosomic mothers, only 16.1% being found, whereas trisomic mothers gave 52.8% trisomic young. Surviving monosomics of both sexes were smaller than trisomics at birth and tended to have unusual skeletal fusions. Both types of aneuploid male were sterile, but tertiary monosomics were less severely affected, as judged by testis mass, sperm counts, and the appearance of testis sections. Both tertiary monosomic and trisomic females have smaller litters than normal females. Possible reasons for these findings are discussed, as well as recent observations throwing light on mechanisms of sterility in this type of translocation.