Chromosomal evolution in higher plants / G. Ledyard Stebbins.
- George Ledyard Stebbins
- Date:
- 1971
Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
Credit: Chromosomal evolution in higher plants / G. Ledyard Stebbins. Source: Wellcome Collection.
114/232 page 102
![102 CHROMOSOMAL CHANGES AND SPECIATION CHAP. 4 II. Ill |H IM 12 3 X Y, Ya North Carolina |l!*| Texas Flg. 4.14 Karyotypes of the Texas and North Carolina races oi Rumex hastatulus, showing the gametic complement of autosomes and the somatic complement of sex chromosomes which exist in male plants. (From B. W. Smith.^®'') a chain trivalent of sex chromosomes is formed. It becomes oriented on the spindle of the first division in such a way that the X chromosome, lying in the middle of the chain, passes to one pole and the two Y chromo¬ somes (Y]^, Y2) pass to the other pole. The X chromosome differs from that in the Texas race, being larger and having a median rather than a subterminal centromere. The two Y's of the North Carolina race are both smaller than the single Y of the Texas race, but their combined length is greater. The smallest pair of autosomes in the Texas race is missing in the North Carolina race. The North Carolina race has a more specialized karyotype than the Texas race, and must be regarded as derived from it. The simplest hypothesis to account for its origin is to assume the occurrence of two successive translocations, by means of which the essential chromatin of the smallest pair of autosomes in the Texas race became attached to arms of both the X and Y chromosomes, while the centromere of this](https://iiif.wellcomecollection.org/image/b18036594_0115.JP2/full/800%2C/0/default.jpg)
