Primitive Genetic Mechanisms and the Origin of Chromosomes

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Abstract
-During the early evolution of life, primordial cells were presumably capable of self-reproduction even prior to the appearance of a mitotic cycle and the refinement of its cytological apparatus. It is postulated that in such primitive "cells," gene-bearing particles were not linked into chromosomes and were segregated at random to daughter cells. The genetic consequences of such amitotic reproduction may be predicted from basic probability considerations. A cell containing n separate gene particles, replicated an average of k times each, would enjoy a probability of successful division (each daughter cell obtaining at least one haploid set) of (1 - l/2k-1)n. Expressions have been derived for the probability of survival of both, one, or neither daughter cells. It has been computed that for amitotic clones to survive, a ploidy of about 8 was minimal. Survival without mitosis could be improved by increase of k (endopolyploidy) or decrease of n (linkage). The former, which requires the synthesis of nucleic acid merely for the sake of redundancy of information, is less efficient than the formation of chromosomes. Various mechanisms for the origin of chromosomes and the possible implication of sexuality in the process are discussed.