Half-mutant

Half-mutant is a mutant which appears in complex-heterozygous hybrid progeny between species of Oenothera lamarckiana and Oenothera rubrinervis, resulting in modified non-lethal genomes accompanied by non-modified genomes in both male and female gametes. Each generation of such generated mutants give rise to so-called "full-mutants“ containing the modified non-lethal genome in double copies.

Half-mutants produce two genetically different types of gametes, resulting in both lethal and nonlethal zygotes. Therefore, they have an unbalanced lethal genome. In order to resolve this, half-mutants, through a breeding process known as selfing, yield a progeny consisting of 2/3 repetition of the half-mutant genome, and 1/3 pure homozygous individuals, resulting in a double dose of non-lethal complexes. Scientists attempted to determine how a half-mutant may be formed from O. Lamarckiana with partial interchange between the ends of opposing complexes; incidentally, this attempt ended up referencing the fact that the non-lethal complex of a half-mutant formed as a result by segmental interchange cannot give the same chromosomes contents in diakinesis with both complexes of the parent species. In the case:

"If it gives a circle of 6 with one, it will give a circle of 8 with the other; if it gives a circle of 4 with one, it will give a circle of 10 with the other; if it gives 7 pairs with one, it will give a circle of 12 with the other. Since that paper was sent to press, however, a paper by S. E. Emerson has appeared (1930), in which it is pointed out that the lethal-free complex of rubricalyx "Afterglow," known as hlatifrons, when combined with the two complexes of Lamarckiana, velans, and gaudens, yields a circle of 8 and 3 pairs with both of them. Assuming that Emerson's data are correct, it becomes necessary to explain this behavior of rubricalyx "afterglow" on the basis of segmental interchange, if the theory is still to be regarded as a possible basis of half-mutant formation in Oenothera. That a satisfactory explanation can be found is indicated by the following paragraphs. Let the complexes of Lamarcktana be arranged hypothetically in such a way that, with like ends uniting, the circle of 12 and one pair characteristic of this species is obtained, as follows (gaudens chromosomes belonging to the circle are in italics): velans = 1-2 39. 5-6 7-8 9.10 11-12 13-14 gaudens = 1 4 3-6 5-8 7-10 9-12 11-2 13-14."

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