Investigation of possible age effects on meiotic chromosomal recombination and segregation in Armenian hamster spermatocytes.

Male Armenian hamsters were evaluated for age effects upon meiotic recombination and aneuploidy incidence. Primary spermatocytes from young and old animals revealed similar chiasma frequencies. The incidence of terminal-type chiasmata in sex bivalents was also measured and found to be unaffected by age. Percentages of univalents and of hyperploid metaphase II cells were evaluated by chromosome groups based upon individual chromosome morphologies. Regardless of age, the larger dichiasmate chromosomes were seldom observed as univalents, or as extra chromosomes in hyperploid cells. The monochiasmate small autosomes and sex chromosomes revealed univalent frequencies approximating to 5.5-6.5% in animals from both age groups. However, only the small autosomes appeared to be significantly implicated in hyperploidy. Although still a rare event, metaphase II hyperploidy was significantly increased in older animals (0.9% incidence in young and 2.4% in old hamsters). The events leading to higher aneuploidy levels in older male Armenian hamsters are not clear. A role for reduced meiotic recombination as a function of age cannot be ruled out in the present study. However, there was no support for this hypothesis, and consideration of other possible mechanisms of age effects to increase aneuploidy levels is indicated.