On the Number of Chromosomes and the Type of Sex-chromosomes in Man
1934 年 5 巻 4 号 p. 472-490
詳細
1934 年 5 巻 4 号 p. 472-490
1. The spermatogonia of a Japanese man show forty-eight chrcmosomes. But it is difficult to locate the unpaired chromosomes X and Y in the spermatogonial chromosome-complex. The serial arrangement is of no service, as is illustrated by the example of Trixalis nasuta in which the chromosomes are much larger in size and much fewer in number than in man.
2. In the first maturation division the chromosomes are twentyfour in number. The sex-chromosome and twelve large tetrads encircle the Small ones so as to form a rosette in the metaphase of the first division.
3. The sex-chromosome is composed of two heteromorphous elements, a long and a short rod. It lies at the periphery of the equatorial plate in the normal condition. Sometimes it is displaced into the centre of the equatorial plate by the effects of the fixation. There is no evidence that the sex-chromosome is of V-shape as reported by Oguma et Kihara, and Winiwarter et Oguma.
4. The X and Y elements conjugate lineally in the first meiosis as is the Gase in all mammals. This mode of conjugation has been reported by Minouchi as asymmetrical synapsis.
5. These elements separate in the first meiosis; as a result, one of the daughter cells receives the X-element and the other the Y-element, so that in the metaphase of the second division each of the germ-cells contains twenty-four chromosomes.
