Parental age and the life-span of zygotes of Saccharomyces cerevisiae.

Isolated cells of Saccharomyces cerevisiae were mated by micromanipulation and the reproductive capacity of the resulting zygotes was determined. The mating frequency was dependent on the age of the parents: conjugations between young cells and cells which had completed more than two thirds of their life-span were very rare events. The life-span of a zygote was very similar to the life-span of its shorter-lived parent. If one of the parent cells had budded several times prior to fusion, the life-span of the zygote was reduced correspondingly, i.e. there was no 'rescue by hybridization.' In four crosses the distribution of buds on both of the parent cells was recorded. In three of these four crosses the buds were evenly distributed, and in one the alpha-parent had three times as many buds as the a-parent.