Abstract
Prior to meiosis in triploid gynogenetic all-female forms of Poeciliopsis, the chromosome number of the nucleus of the triploid oogonium is raised endomitotically to hexaploid. Recombination does not occur; instead, a triploid ovum with a genetic complement identical to that of the mother is produced by two conventional meiotic divisions. Sperm from a sympatric gonochoristic (bisexual) species stimulates the ovum to develop, but paternal genes are not incorporated into the zygote. This is the first cytologically verified case of natural endomitosis in the egg production in fish.
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