The relation between the number of chromosomes of a species and the rate of elimination of mongrel blood by the pure-sire method

Summary

1. Mongrel “blood” is eliminated by the pure-sire method not by “quartering out,” but in segments, in degree governed by the relative ontogenetic potency of the particular chromosomes eliminated.

2. The degree of elimination of mongrel “blood” by the puresire method depends upon two factors, (a) the number of chromosomes characteristic of the species, (b) the proportion of mixed dams of each possible pure chromosome-number used in each generation, (c) the relative fecundity of dams of different pure chromosome-number, and (d) the number of generations through which the system is carried.

3. By the pure-sire method, without selection in the F₅ generation in a twelve-chromosome (haploid) species (including man), the probability that a given offspring carries absolutely no mongrel blood, i. e., mongrel-descended chromosomes is 1 :0.205.

4. For mass improvement without selection the pure-sire method in a twelve-chromosome (haploid) species, ceases to be practically effective after the F₅ generation.