PROBLEMS WITH INDOGAMIC LINES. lll. HETEROSIS BETWEEN SISTER LINES

Abstract

A theoretical analysis is made on the resulting heterosis when crossing sister lines or sublines derived from de same line head, for four types of inbred lines: selfed, full-sibed, half-sibed, and backcrossed lines. The objective is to discuss their use in single crosses between pair of sublines to obtain three-way crosses with a third non-related line. With selfed lines the genetic mean of the F₁ is always the same irrespective of the inbreeding coefticient of the sublines, and is equal to the mean of one S₁ line, while heterosis increases as does inbreeding. For fullsibed and half-sibed lines the same happens if it is assumed that the frequencies of dominant homozigotes and recessive homozigotes are equal (symetry of homozygotes frequencies), with the only difference of the involved inbreeding coefficient. For backcrossed lines mean heterosis is nega.tive, thus this type of lines is not recomended for the refered use.