Variation in chiasma frequency during tulip anther development

Meiotic variation in an intergenomic autopolyploid series. I. Chiasma frequency

Variation in chiasma frequency has been studied in PMCs of diploids and C0 autotetraploids of seven Lathyrus species exhibiting a range of genome size (10.8-19.9 pg DNA/2C). Variation in chiasma frequency showed no relation to changes in genome size, either between species or between disomic sets within nuclei. Mean chiasma frequency of the tetraploids showed a 75% increase over that in the diploids. Half of this increase represents an additive effect of chromosome doubling. Total variance in chiasma frequency of autotetraploids increases by 80% over that in diploids, in line with the square of the multiplicative effect of chromosome doubling. At the diploid level, interspecific differences account for the major component of variance (63.1%). Phenotypic variation in chiasma frequency was apparent in all seven species but represented the smallest component of variance (2.8%). Chromosome doubling results in an eightfold increase in the absolute size of the phenotypic component of variance in chiasma frequency and a threefold increase in that of the cellular component. It has no effect on the absolute size of the interspecific component.

Metaphase I bound arms frequency and genome analysis in wheat-Aegilops hybrids : 1. Ae. variabilis-wheat and Ae. kotschyi-wheat hybrids with low and high homoeologous pairing

Meiotic associations of different wheat-Aegilops variabilis and wheat-Ae. kotschyi hybrid combinations with low and high homoeologous pairing were analyzed at metaphase I. Five types of pairing involving wheat and Aegilops genomes were identified by using C-banding. A genotype that seems to promote homoeologous pairing has been found in Ae. variabilis var. cylindrostachys. Its effect is detectable in the low pairing hybrids but not in the high ones. Pairing affinity has been analyzed on the basis of metaphase I associations in the low and high homoeologous pairing hybrids, and in bivalents and multivalents in the high pairing hybrids. The results indicate that the amount of bound arms of each type of identifiable association relative to the total associations formed (relative contribution) was not maintained, either between the different levels of pairing (low and high) or between different meiotic configurations (bivalents and multivalents). These findings seem to indicate that quantifications of genomic relationships based on the amount of chromosome pairing at metaphase I must be carefully done in this type of hybrid combinations.

Chiasma-derived genetic lengths and recombination fractions: a reciprocal translocation 46,XY,t(1;22) (q32;q13)

The chiasma distribution in a human male carrier of a balanced reciprocal translocation 46,XY,t(1;22) (q32;q13) has been compared with data from six controls. The translocation carrier shows a raised chiasma frequency and altered chiasma distribution in chromosome 1, particularly in the region adjacent to the breakpoint. These changes are expected to distort the recombination pattern, implying that caution should be taken when trying to incorporate linkage data from translocation families into the normal genetic map.

Correlation between chiasma frequency and quantitative traits in upland cotton (Gossypium hirsutum L.)

Four locally adapted and high yielding cultivars of upland cotton were examined in order to elucidate the relationship between total chiasma frequency and quantitative traits, including yield and fiber properties. Total chiasma frequency per nucleus was found to correlate positively with boll number (r = 0.4041), seed cotton yield (r = 0.6003), seed index (r = 0.4624), lint yield (r = 0.7325), and lint index (r = 0.9534). The data are discussed from the point of view that the heterozygosity caused by increased chiasma frequency in inbreeding cotton cultivars is an important compensating mechanism for enhancing effective recombination and genetic variability.

The effects of ageing on the meiotic chromosomes of male and female mice

The effects of age on the chiasma frequencies, chiasma position and numbers of univalents at MI in males and females of three strains of mouse were examined. Males showed a slight but non significant rise in chiasma frequency in age due to an increase in bivalents with two chiasmata at the expense of single chiasmata bivalents. In contrast, females exhibited a significant decrease in chiasma frequency with age due to the loss of two chiasma bivalents with a corresponding increase in single terminal chiasmata bivalents. In both males and females there was no significant increase in univalents with age in the strains studied. Of interest was the finding of a greater degree of contraction of the MI chromosomes in the oocytes of old relative to young females, a differential contraction that was independent of culture time. This finding is discussed with regard to the "production line theory" and non disjunction at Anaphase in other strains of mice.