1. The case is reported of a chromosome termedscYL formed by rearrangement between theY-chromosome and anX containing thescS1 inversion. The rearranged chromosome has on one side of its centromere the whole of the long arm of the normalY and on the other side a small section invisible in mitotic stages, containing the left distal end of theX, with the scute gene and the normal alleles of genes to the left of it.
2. If the breakage and reunion occurred by a process of crossing-over, the chromocentral regions ofX andY here involved must have been in inverted position in regard to each other or else adjacent instead of diagonally opposite ends of the conjugating chromosomes must in this case have become attached together.
3. In its new position on theY-chromosome the scute gene has an expression similar to that on its old position on theX-chromosome. Moreover the position effect is of a mosaic nature in theY as in theX.
4. When thescYL forms a duplication ofsc, the scute effect is reduced and theHw effect accentuated, the body colour is darkened and the homozygousscS1 female (usually sterile) is rendered fertile; bristles are longer and thicker, and general viability is increased. In non-scute flies thescYL adds bristles in the dorsocentral region, and gives a slightHw effect.
Volume 100, 2021
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