Untersuchungen über die Entstehung der Parthenogenese bei Solenobia triquetrella F.R. (Lepidoptera, Psychidae)

Summary

• 1. The 2n form of Solenobia triquetrella found at Alpe di Melano shows an unpaired X and, in addition, two pairs of special chromosomes differing in size: aa and bb.

• 2. During the maturation divisions in the egg two different special chromosomes remain permanently bound to each other (ab), while the respective partners remain independent without exception a/b.

• 3. The distribution of the special chromosomes in the reduction division is at random and is independant of the distribution of the X. Thus the 4 possibilities of combination (ab) + X:a/b + X:(ab)+-: a/b+- (Fig. 2) occur at a 1∶1∶1∶1 ratio.

• 4. Two interpretations offer themselves:

• a) In moth with compound chromosomes (e.g. Phragmatobia fuliginosa, Lymantria monacha) it can be shown, that compound chromosomes are formed in successive steps and that the caryotype is gradually changed (Fig. 4).

  The analogous may be true for S. triquetrella. Two different special chromosomes have combined to form a compound chromosome (ab); in this first phase of change, the partners remain independent a/b. Probably a second stage will follow leading to a caryotype with two compound chromosomes, each consisting of two single chromosomes (ab), (ab).

• b) More likely is the second possibility, that we are dealing with a reciprocal translocation between two different special chromosomes (Fig. 5). The mutated chromosomes a ₁ b ₁ are bound together (a ₁ b ₁), the non-mutated ones remain free a/b.

  As a hypothesis we assume that the binding together of a₁ and b₁ is caused by the constitution of the point of breakage and reunion.

  During meiosis both tetrads (a₁ b ₁) and a/b form a double tetrad, since both have homologous segments (Fig. 5). As shown by direct observations this double tetrad splits into its components (a ₁ b ₁) and a/b at a 1∶1 ratio.