The frequency of pollen mother cells with univalent chromosomes at first metaphase was determined in five varieties and ten varietal hybrids of vulgare wheats. The proportion of cells with univalents in the varieties varied from 2.9 per cent to 9.7 per cent and in the hybrids from 5.2 to 39.1 per cent. Hybrids between related varieties on the whole gave lower univalent frequencies than those between unrelated varieties, but exceptions occurred. In any cell with univalents two was the most common number, and as high as eight were observed. Trivalents and tetravalents were seen only rarely. Wide variation in percentage of cells with univalents was observed in some instances. Higher univalent frequency occurred in first metaphase cells from anthers in which most of the cells were well past metaphase. No significant difference in univalent frequency was found in two groups of Marquis plants kept under fairly constant temperatures the respective means of which were 60° and 77°F. The univalents in different cells were of different sizes and shapes. In certain hybrids with high univalent frequency, the univalents seemed to be longer than in certain varieties. Attenuated bivalents and bivalents with fewer chiasmata were more frequent in hybrids with frequent univalents. Typical metaphase bivalents are drawn and the number of chiasmata estimated for each. Terminal or terminal and closely sub-ter-minal chiasmata are the rule but exceptions occur. Configurations resembling some of those interpreted by HUSKINS and by POWERS as trivalents are here interpreted as bivalents. It is to be expected that the occurrence of univalents will give rise in the next generation to plants with abnormal chromosome numbers and to disturbed genetic ratios. The relationship of these observations to the chiasma theory is discussed and it is concluded that they support DARLINGTON's theory which ascribes the occurrence of univalents to a reduction in frequency of chiasmata.
A recessive partially sterile type of maize is reported to which has been given the narre variable sterile and the genetic symbol va. Variable sterile plants are characterized by lack of cytokinesis during the meiotic divisions of some of the microsporocytes. Accompanying the failure of cytoplasmic division, aberrant chromosome behavior often is observed. Presumably as a result of these aberrations in chromosome behavior, most if not all of the resulting 2n and 4n cells degenerate. Variable sterile plants produce, for the most part at least, diploid progeny indicating again that only the, haploid gametes are funetional. The va gene is located in the Bn-gl1-v5-ra chromosomes roughly 10 units to the left of gl1.
1. CHAMPY'S mitochondrial fixative after original formula has yielded most favourable results for chromosomes of Hemidactylus bowringii, and FLEMMING'S strong solution containing no acetic acid for those of Gekko japonicus. 2. Hemidactylus bowringii has 46 telomitic chromosomes intergrading from a long rod to a small dot, and Gekko japonicas 38 chromosomes, 4 large V-shaped and 34 telomitic ones of various sizes. 3. Concerning the original chromosome complex of the family Gekkonidae we have no decisive evidence as yet; however, between the chromosome complex of Gekko japonicus and that of Tarentola mauretanica, there seems to be such relationship that a V-shaped chromosome of the former corresponds with two non-homologous rodlike chromosomes of the latter. 4. The sex-chromosomes of the males of those geckos are two short rod-like ones of the homomorphic type. They are distributed equally into each spermatid through the meiotic divisions.
Observations on meiosis in male Stenobothrus parallelus show that:- 1. Randomness of chiasma distribution is modified by “interference”; the mean frequency is more than five times the variance. 2. Randomness of chiasma frequency is modified by an indirect relationship to size such that while the long chromosomes are seven times the length of the short, they have only three times as many chiasmata. This is a genetic adaptation to secure regular pairing with a wide range of size of the chromosomes, and may occur in Drosophila. 3. In eight analysed cases the successive chiasmata were relatively “compensating ”. 4. Terminalisation in this species is slight. It consists merely in the expansion of loops at the expense of free arms and of the attachment loop at the expense of other loops. Considered in conjunction with similar studies on Tulipa, Campanula and other genera, these observations suggest an electrostatic explanation of terminalisation which is in accordance with the general behaviour of the chromosomes at these stages of their development. We are indebted to Prof. J. B. S. HALDANE for criticism.
Die rheotaktische Geschwindigkeit, d.h. Geschwindigkeit, mit der die Spermatozoen gegen den Strom vorrücken, wurde beim Pferd in einer Kapillare und zwar bei einer konstanten Temperatur von 37°C gemessen. Die Ergebnisse lassen sich im Folgenden zusammenfassen: 1. In stromloser Flüssigkeit beträgt der Mittelwert der Geschwindigkeiten der Spermatozoen 86, 7±3, 80μ pro Sekunde. 2. Die absolute Geschwindigkeit der Spermatozoen in strömenden Flüssigkeiten ist gar nicht konstant, sondern sie schwankt je nach Stromsärke innerhalb weiter Grenze. 3. Das Optimum der Stromstärke für die Rheotaxis der Spermatozoen liegt bei 20μ pro Sekunde, da die allermeisten Spermatozoen bei dieser Stromstärke rheotaktisch reagieren. 4. Der Mittelwert der absoluten Geschwindigkeiten der Spermatozoen in strömenden Flussigkeiten kann mit demjenigen bei der optimalen Stromstärke bezeichnet werden. Er ist als 107, 1±1, 33μ pro Sekunde ermittelt worden. 5. Wenn die Zahl der rheotaktisch reagierenden Spermatozoen auch allmählich geringer wird, steigt ihre absolute Geschwindigkeit mit Stromstärke Hand in Hand auf. 6. Die Aufsteigung der absoluten Geschwindigkeit der Spermatozoen mit zunehmender Stromstärke bedeutet jedoch keine Erregbarkeit der Spermatozoen durch Strömungsreiz. Dies beruht vielmehr darauf, daß die Spiralbahn der Spermatozoenbewegung durch Strömung nach einer geraden Richtung gezogen wird, und die Strecke, die die Spermatozoen gegen den Strom zurücklegen, dementsprechend vergrößert wird.
1. The relations between three different lines of Pisum sativum, the K line, the T line and the N lines, are discussed, with regard to chromosome structure. All three lines have seven pairs of chromosomes at meiosis. The K line when crossed with N lines was found by HÅKANSSON to give a ring of four chromosomes at meiosis. Similarly the T line gives a ring of four chromosomes with N lines. The K line when crossed with the T line gives an association of 6 chromosomes at meiosis. 2. This shows that the K line and the T line are related to N lines by a single interchange of chromosome segments and to each other by a double interchange, involving three chromosomes of the haploid set. 3. Metaphase pairing is found to be due to chiasma formation, interstitial as well as terminal chiasmata being present at metaphase as in previously described Pisum plants. 4. About 78% of the configurations of six chromosomes examined have an interstitial chiasma, the “median chiasma, ” between nonadjacent chromosomes of opposite parental complements. When this chiasma is present, the configurations assume the shape of a “figure-of-eight, ” similar to that described in Oenothera by DARLINGTON (1931). 5. The presence of the “median chiasma” shows that an homologous interstitial segment is present in the otherwise non-homologous chromosomes taking part in it. A hypothesis is put forward to explain the origin of this segment. 6. The “figure-of-eight” is shown to be a cytological demonstration of previous genetical crossing-over, on the single assumption that only homologous parts of chromosomes pair. This crossing-over gives segmental interchange between chromosomes only homologous in an interstitial region. 7. As a result of this segmental interchange, there are four viable gametic types containing n-chromosomes possible, namely the two parental types and two new types containing the interchanged chromosomes. The different possible zygotic combinations to be obtained on selfing this plant are predicted. Instead of the progeny being restricted to plants with simple pairing and plants with associations of six chromosomes at meiosis, plants with rings of four chromosomes are expected, as a result of the new combinations resulting from segmental interchange. 8. A re-examination of the ring of four chromosomes formed when the T line is crossed with N lines showed the presence of chiasmata on both sides of the attachment constriction in one pair of segments, in some cases. This demonstrates that the point of attachment is at some distance from the place where the change of segment occurs. It is suggested that such configurations occur also in Zea Mays and in Datura. The author desires to thank Miss C. PELLEW for supplying the material for cytological study, Dr. C. D. DARLINGTON and Dr. F. W. SANSOME for criticism and advice, and Mr. H. C. OSTERSTOCK for taking the photomicrographs and for assistance with the diagrams.