Showing papers in "Theoretical and Applied Genetics in 1973"

The relation between hybrid vigour and genotype-environment interactions

Abstract: Consideration was given to the response curves and response surfaces that are obtained when genotypes are grown at various levels of environmental factors. These curves and surfaces were used to illustrate genotype-environment interactions and possible relations between two parents and their F1.

The mechanism of maternal inheritance in Chlamydomonas: Biochemical and genetic studies.

Abstract: The cytoplasmic linkage group of Chlamydomonas shows maternal inheritance, i.e. preferential transmission of cytogenes from the female (m t+) parent and loss of the corresponding male (m t−) genome in sexual crosses. The mechanism of this process is postulated to be enzymatic modification of chloroplast DNA of the female to protect it from a restriction enzyme which degrades the chloroplast DNA of the male parent in the zygote soon after fusion. Genetic, biochemical and physical data bearing on this hypothesis are summarized and discussed.

Mutations leading to nuclear restoration of fertility in S male-sterile cytoplasm in maize

Abstract: Among the offspring of crosses involving S male-sterile shrunken-2 inbred lines and their corresponding isogenic maintainer lines a number of exceptional male-fertile plants were identified. Some of these were plants with entirely fertile tassels but most were chimeras involving both sterile and fertile tassel elements. The majority of male-fertile exceptional plants, upon crossing with male-sterile testers, produced male-sterile test-cross progeny, indicating that the male-fertile trait is not pollen transmissible. However, there were four separate instances, involving three of the inbred lines, in which the crosses with S male-sterile testers produced male-fertile progeny, indicating that the newly arisen male-fertile trait is pollen transmissible. In three of these cases, the male fertility can be traced to a single plant in essentially male-sterile families. The fourth evidently involved a change in a maintainer plant whose progeny thereafter segregated for the ability to restore S sterile cytoplasm. In all cases, the results of progeny tests are consistent with the gametophytic pattern of restoration associated with S male-sterile cytoplasm. The male-fertile exceptions described here can be accounted for formally as mutations at one or more restorer gene loci in the nucleus. Taking account of the fact that mutations of restorer genes have not been reported previously in maize, and that four such changes were encountered in the same strains in which we have identified other male-fertile exceptions involving change in the cytoplasm, we have suggested a common basis for the two kinds of events. According to this scheme, given the first appearance, by whatever process, of the male-fertile element in sterile cytoplasm, it may become established and continue to propagate either in the cytoplasm or in the nucleus. In the former case, the change registers as cytoplasmic and the new strain has the characteristics of a maintainer which transmits the male-fertile trait through the egg, but not the sperm; in the latter case, the change occurs in the nucleus and the new strain, now behaving as a restorer, transmits male fertility through both egg and sperm.

Evolutionary trends in Vicia faba L.

Abstract: 1. Distances have been calculated between thirty natural populations of Vicia faba. 2. The results strongly suggest the existence of a Central Nucleus from which different trends of evolution have arisen. 3. The Central Nucleus represents the equilibrium between different genetic tendencies; this equilibrium is postulated for the primitive populations of this species. 4. Disturbance of this balanced system can be produced by cycles of cross and self-fertilization; recombinations following these cycles are the origin of new genetic combinations so that a new equilibrium is reached with a new cycle of disturbance. 5. The Muratova classification is discussed. It is not possible to give a new classification based on these concepts, because of the great number of possible lines of evolution. The species must be considered as a whole, because there are no genetic barriers of isolation, only geographical ones and no sterility barriers have been produced between the subspecies. 6. A description of the Central Nucleus of Evolution is given.

Quinacrine fluorescence and Giemsa banding in trisomy 22.

Abstract: Using quinacrine fluorescence and Giemsa banding techniques we have identified an extra chromosome 22 in three non-mongoloid children with similar phenotypes and 47 chromosomes. In one of the children, the long arm of the extra 22 was shorter than usual. This 22q—chrcmcscme was observed in 4 normal family members with 46 chromosomes. In a fourth child, with similar physical findings, the extra G chromosome was shown to be neither a normal 21 nor 22. It must have arisen from a rearrangement in a parental gamete since it was not present in either parent's karyotype. No constellation of clinical findings, in association with an extra G chromosome, is sufficient evidence for the diagnosis of trisomy 22. The positive identification of the extra chromosome must be made using fluorescence and banding.

Genetic studies of self incompatibility in the garden chrysanthemum, Chrysanthemum morifolium ramat.

Abstract: Self incompatibility was investigated in the hexaploid garden chrysanthemum, a member of Compositae. Nine sibling clones selected from a highly compatible cross were all self incompatible. 14.8% of the crosses between these sibs in diallel were compatible, but one sib, 67-111-42, accounted for 10 of the 12 compatible crosses. 67-111-42 was also more compatible than the remaining 8 sibs in crosses to other closely related plants. Crosses of the 9 sibs to 12 unrelated tester clones indicated that none were male or female sterile. Inbreeding via pseudocompatibility was successful in increasing homozygosity at the S loci. The percentage of compatible crosses obtained in 3 sib diallels of I2 clones from crosses of 67-111-42I1 plants approached that of the original 9 × 9 diallel, but no one individual accounted for most of the compatible crosses. It was possible to separate the 9 sibs into 9 incompatibility patterns from the pollinations made in this study. The evidence suggests that the self-incompatibility reaction in the garden chrysanthemum is sporophytic and involves more than 1 locus.

Variability of essential amino acid content in seeds of 22 Phaseolus species.

Abstract: The reserve protein composition of 22 Phaseolus species has been studied. The non-sulphur-containing amino acids were present at values higher than those suggested for animal (and human) nutrition, but the sulphur-containing amino acids, with some exceptions, were under the minimum accepted requirement. However, taking into account the variability in the percentages of methionine and cystine, as well as the cystine/methionine ratio, it is concluded that the genus Phaseolus has a theoretical possibility for synthesizing a reserve protein with a balanced sulphur-containing amino acid content. An accession from Mexico of the species Ph. phyllanthus possesses a protein characterized by a high sulphur-containing amino acid content (3,84%). The possible utilization of this species in breeding for legume protein quality is suggested. Some observations about the percentage of arginine in wild and cultivated forms of Ph. Vulgaris are also presented.

Studies of dotted, a regulatory element in maize : I. Inductions of dotted by chromatid breaks II. Phase variation of dotted.

Abstract: Dotted (Dt) is the regulatory element of a two-unit controlling system in maize. Dt causes the inherited change from the recessive a 1 (colorless) to its dominant allele, A 1 (anthocyanin production), during the development of the stalk, leaves, and endosperm. The mutation events are observed as sectors of color in an anthocyaninless background.One of the most puzzling, but perhaps significant, aspects of controlling elements in maize is that they originate in conjunction with chromosome or chromatid breaks. This fact invokes a requirement that either an existing regulatory mechanism is disturbed by the breakage or that a foreign element is incorporated before fusion of the broken chromatids.Experimental crosses were made between Dt tester stocks and a pollen parent, a large proportion of whose chromosomes 9 were undergoing the chromatid type of bridge-breakage-fusion cycle. New Dt's were induced in endosperm sectors of 250 of 154,422 kernels tested (1/600); among these, two germinal Dt's (Dt (crown) 4 and Dt 5) were recovered, presumably due to chromatid breaks during meiosis or the first microspore division. Dt 5 produces a mutation pattern very similar to the original Dt 1 and is located 0.33 crossover units away from the yg 2 locus. This is close to the known location of Dt 1 (7 crossover units distal to the yg 2 locus) and is suggestive of a specific site for Dt inductive breaks. Dt (crown) 4, on the other hand, is inherited independently of the yg 2 locus and does not support this contention. Dt (crown) 4 represents a new "state" causing a high concentration of fine dots in the crown of the kernel, with little or no dotting at the base.The phase variation of Dt (crown) 4 is discussed together with the tissue-dependent expression of Dt (in-ac) 1 (Dotted, inactive-active). Dt (in-ac) 1 is a new "state" of Dt 1 and shows inactive (no a 1 to A 1 mutations) and active (a 1 to A 1 mutations) phases in the endosperm, whereas it is only in the active phase in the diploid scutellum. The observed phase variation was shown to be a property of the regulatory elements, Dt, responding to differences in the cellular environment.

Sexual dimorphism and direct and maternal genetic effects on body weight in mice.

Abstract: Genetic and phenotypic parameters for three-, six- and eight-week body weight and for weight gain between three and six weeks of age were estimated from data collected over 14 generations in a randombred control population. Genetic parameters were also estimated for sexual dimorphism in body weight and gain. Heritability estimates were substantial for body weight at all ages and for body weight gain. Additive maternal variances were also large. Estimates of the covariance between direct and maternal genetic effects were negative and substantial for three- and six-week weights and gain. Also the covariance between maternal effects on weaning weight and direct genetic effects on six- and eight-week weights were negative. These results indicate a consistent antagonism between maternal and direct genetic effects in this population.

A Study on the nature of genetic divergence in rice from assam and North East Himalayas.

Abstract: A representative group of 190 rice types collected from North-East India along with four standard varieties, three of which were indicas and one japonica, was studied to understand the nature of genetic divergence. Preliminary grouping was done by canonical analysis and the resultant 42 groups were further classified using the D2 statistic. The final grouping resulted in nine divergent clusters. The three indica standards were found in three different clusters indicating the wide available variability among them. The japonica standard formed a separate group by itself. A majority of the North-East Indian types formed clusters with indicas, whereas some were intermediate and still others were closer to japonica or indica, thus indicating a series of intergrades bridging indica and japonica. Height followed by leaf area was found to be important for primary and 100-grain weight, followed by amylose content for secondary differentiation. It appears that natural selection as well as human selection might have operated for characters differentiating rice types in Assam and North Eastern Himalayas. Geographical distance was not found to be related to genetic divergence. The study suggests that O. sativa contains innumerable but divergent forms, and its classification into definite varietal groups on an arbitrary basis such as isolation barrier, sexual affinity or geographic distribution would be far from reality.

Evolution and improvement of cultivated amaranths

Abstract: Of the four interspecific hybrids, three (A. graecizans var. graecizans X A. tricolor cv. ‘Purple leaf’, A. lividus var. lividus X A. tricolor var. viridis and A. gracilis X A. tricolor cv. ‘Purple leaf’) were studied cytologically. In all the three, differentiation between the parents is chiefly a result of interchanges and paracentric inversions. The interchange complexes may involve from four (A. gracilis X A. tricolor cv. ‘Purple leaf’) to fourteen (A. lividus var. lividus X A. tricolor var. viridis) chromosomes, indicating that the parents differ from each other in 1 to 6 interchanges. Because of the small size of the chromosomes, it is possible that crossing-over in interchange for small segments is restricted. The particular parental species representing the ancestral condition from which others were derived or compounded is difficult to pin-point. With preferential pairing and the restoration of fertility in the amphidiploid A. lividus-tricolor, it became clear that it is very likely that the interchanged segments are small and sterility in the hybrid is entirely chromosomal. This situation is in strong contrast to that in Sect. Amaranthus, where the single male flower per glomerule and huge showy inflorescences lead to more cross-pollination; coupled with this are strong morphological divergences between taxa and less genetic differentiation. In the Sect. Blitopsis, there are a number of male flowers per glomerule and small non-showy axillary inflorescences, leading to self-pollination, and less morphological but strong genetic differentiation by interchanges and inversions.

The modification of crossing over in maize by extraneous chromosomal elements.

Abstract: Five regions of the maize genome were tested for their response to endogenous factors influencing recombination. These included heterochromatic B chromosomes and abnormal chromosome 10 as well as the sex in which recombination occurred.

Genetische Untersuchungen bei Picea abies mit Hilfe der Isoenzym-Identifizierung

Abstract: Using techniques of starch gel zone electrophoresis, a considerable variation among esterase and leucine aminopeptidase isoenzyme patterns was found in the endosperm of dormant seeds of Norway spruce (Picea abies). Since the so-called primary endosperm of conifers is only a further developmental stage of the haploid female gametophyte, simple Mendelian segregations can be determined in seeds of individual open-pollinated trees. It was therefore possible to identify some esterase and leucine aminopeptidase loci only with regard to phenotypic frequency distributions without difficult crossing procedures.

Evolution and improvement of cultivated amaranths : VI. Cytogenetic relationships in grain types.

Abstract: This group of amaranths was studied using four domesticated species (A. hypochondriacus, A. cruentus, A. caudatus, A. caudatus var. atropurpureus and A. edulis), two ancestral weedy species (A. hybridus, A. powellii) and eight hybrids, namely A. edulis A. hypochondriacus, A. edulis X A. caudatus, A. edulis X A. caudatus var. atropurpureus, A. caudatus X A. hybridus, A. edulis X A. hybridus, A. caudatus X A. hypochondriacus, A. hybridus X A. hypochondriacus and A. powellii X A. hypochondriacus.The parents have perfectly normal meiosis and pollen and seed fertility. Except for A. powellii and A. cruentus (n = 17), the species have n = 16. However, the hybrids may be divided into three groups. The first group contains A. edulis X A. cruentus, involving parents with n = 16 and 17, which failed totally, although, under the same conditions, crosses between A. powellii (x = 17) and A hypochondriacus (n = 16) and those between species with n = 16 succeeded with ease. The second group is made up of A. edulis X A. hypochondriacus, A. caudatus X A. hypochondriacus, A. caudatus X A. hybridus, A. edulis X A. hybridus and probably also A. powellii X A. hypochondriacus. Of these, the two combinations, A. caudatus X A. hybridus and A. edulis X A. hybridus, did not proceed beyond the two-leaf stage. At pachytene, the other hybrids showed unmistakable evidence of structural hybridity, with deletions, long or short differentiated segments and inversions. Although bivalents were formed, they possessed a chiasma frequency lower than that of either parent. There was total pollen and seed sterility.The third group comprises A. edulis X A. caudatus, A. edulis X A. caudatus var. atropurpureus and A. hybridus X A. hypochondriacus, which did not show serious developmental defects, the F1 being vigorous, with good meiotic pairing associated with a reasonable amount of differentiation in the chromosomes leading to 25- 55% fertile pollen and 49 to 66% threshable seed. In the F2 there were 11-18% unthrifty plants, which disturb the ratios of gene combinations controlling the different characters in the two parents. Plants very near one or both parental phenotypes were recovered, and also those showing different degrees of recombination of characters. Amphidiploids from the F1 hybrids showed the typical autoploid or segmental alloploid type of meiosis indicating that the parental chromosomes are quite homologous.In view of the present experimental evidence and possible parallel mutations in different grains and weed amaranths, it is not certain whether the cases of natural hybridization and, in particular, of introgression can be taken as evidence for or against the two hypotheses proposed by Sauer (1967) on the basis of his brilliant ecogeographical, morphological, ethnobotanical and archaeological studies of this group of amaranths.The only point that can be stated categorically is that A. caudatus has given rise to A. edulis. The dominance of the characters of A. caudatus over those of A. edulis strengthens such a view, but the latter is sufficiently differentiated morphologically and genetically to deserve independent status. A. caudatus var. atropurpureus is a fertile but unstabilized hybrid segregate between A. caudatus and A. edulis. This is borne out by its morphological, cytogenetic and breeding behaviour, and its hybrids with A. edulis, and, above all, by the recovery of plants identical with this variety from the F2 progeny of A. edulis X A. caudatus.Whatever the origin of grain types, at present they exist only in cultivation and appear to have a long history, having been selected for large plant body, huge compound inflorescences, large number of female flowers per glomerule, small and soft bracts and pale coloured seed in a dehiscent utricle. At the same time, there has also been inadvertent selection for higher and correctly balanced amounts of protein, carbohydrate and fat.

Intergenotypic interactions among families of loblolly pine ( Pinus taeda L.)

Abstract: The effects of competition on the growth of families of loblolly pine (Pinus taeda, L.) seedlings were investigated. The experimental design made it possible to evaluate the effects of crowding on growth and to determine the types and magnitudes of intergenotypic interactions among pairs of families. The results showed that intergenotypic interactions were both highly variable and pronounced in their effect on early growth. Evidence was also found for precompetition cooperating interactions occurring among seedlings surrounded by neighbors of the same family.

Mechanism of male sterility in Petunia : II. Free amino acids in male fertile and male sterile anthers during microsporogenesis.

Abstract: The free amino acid contents in the anthers of male fertile, cytoplasmic male sterile (cms) and genic male sterile (gms) petunia lines were compared at different developmental stages of the male gametophyte. Quantitative differences in the amounts of free amino acids were found between the fertile and male sterile lines and between the cms and gms lines. The differences between the sterile lines were correlated with the different developmental stages at which the breakdown in microsporogenesis occurred. In the Rosy Morn (RM) cms line, where breakdown of microsporogenesis occurred at the end of prophase 1, there was an associated increase in asparagine and decrease in the other amino acids. In the RM gms line, in which breakdown occurred at the tetrad stage, an accumulation of asparagine in the anthers corresponded with an accumulation of glutamine beginning at prophase 1. Compared with fertile anthers, the sterile anthers accumulated much proline at the early meiotic stages, but no γ-aminobutyric acid. Comparison of the free amino acids of the fertile and the male sterile lines indicates that certain biochemical events leading to breakdown of microsporogenesis precede the observed cytological breakdown. The results from adding asparagine and glutamine to extracts of anthers at different developmental stages suggest that the amino acid balance may contribute to the changes in pH in the fertile and male sterile anthers which we observed previously.

The population genetics of parthenogenetic strains of Drosophila mercatorum : I. One locus model and statistics.

Abstract: A one locus model has been developed to describe parthenogenetic populations restoring diploidy by central fusion, terminal fusion and gamete duplication. It was found that in the absence of selection all populations become homozygous. With selection, however, it is possible to maintain heterozygotes and homozygotes. The conditions required to yield such an equilibrium are a function of (1) the proportions of the various diploid restoring mechanisms (2) linkage to the kinetochore and (3) the intensity of selection. The model was then used to derive one-generation likelihood functions. These likelihoods were used in deriving estimation procedures for the frequency of gamete duplication which is important in forming isogenic lines and for the probability of a heterozygous female giving rise to a heterozygous zygoid. Next, n-generation likelihood functions with and without selection were calculated. These were used to estimate the selection coefficient and to derive two tests of the hypothesis of no selection versus the hypothesis of selection. The first test is a locally best test in the vicinity of no selection, and the second an "odds" for the hypotheses using a prior distribution on the selection coefficient.

Single gene heterosis for alcohol dehydrogenase in maize: the nature of the subunit interaction.

Abstract: The products of the Adh1Fallele which specifies an active enzyme, and the Adh1Cmallele which specifies a stable enzyme, interact in the heterodimer to give an active stable alcohol dehydrogenase. Investigations on the nature of the heterotic interaction are presented including comparisons of in vivo and in vitro synthesized heterodimers.

Biochemical composition of maize (Zea mays L.) pollen : III. Effects of allele X storage interactions at the waxy(wx), sugary (su 1) and shrunken (sh 2) loci on the amino acid content.

Abstract: Pollen grains containing either the Wx, wx, Su 1, su 1, Sh 2 or sh 2 alleles were stored at 0, 1, 2, 3, 4 and 5 days at 2 °C. After each storage period, a portion of pollen from each genotype was analyzed for free amino acid content. Over all genotypes, storage significantly altered the content of all 16 amino acids measured. With increasing storage, a relatively consistent increase in aspartic acid, isoleucine, leucine, phenylalanine, ethanolanine, α aminobutyric acid, NH3 and lysine was found. A relatively consistent decrease in glutamic acid, proline, glycine and alanine occurred with increasing storage. No consistent response to storage was obtained with threonine-serine, valine, histidine and the unknown. Apparently, storage or stage of viability loss has a pronounced effect on amino acid metabolism in maize pollen grains. The experiment was designed so that comparisons free of genetic background effects could be made between alleles at each locus. Significant allele X storage interactions at each locus were found as follows: at the waxy locus, aspartic acid, glycine, alanine and ethanolanine; at the sugary locus, aspartic acid, alanine, ethanolanine and α aminobutyric acid; and at the shrunken locus, aspartic acid, alanine, valine, leucine and ethanolanine. Amino acid metabolism is apparently influenced by the action of the alleles at these loci. The differences between the loci in the amino acids affected indicate the different areas of amino acid metabolism are influenced by each locus.

A test of distributive pairing in Zea mays utilizing doubly monosomic plants.

Abstract: The v x1 deficiency in Zea mays induces chromosomal nondisjunction during the megagametophyte divisions after meiosis producing large numbers of monosomes, trisomes, double monosomes, double trisomes, and even triple monosomes. In this study, microsporogenesis in six doubly monosomic combinations was analyzed. Double monosomes in a diploid organism provide the ideal material to determine if there is an interaction between two nonhomologous univalent chromosomes because two nonhomologous chromosomes lacking partners are present in each meiotic cell. At diakinesis and metaphase I, the two nonhomologous monosomic chromosomes were infrequently “paired” (3.76% and 2.18% respectively). These estimates are the upper estimates of “pairing” of nonhomologous monosomic chromosomes and probably represent an overestimate of these values because cells with any connections between the monosomic chromosomes were scored as having nine pairs and similar connections are not infrequently observed between two bivalents. The transmission of two nonhomologous unpaired chromosomes was deduced by studying the progeny of maize plants hyperploid for two chromosomes (a B4 and Wd ring). The two nonhomologous univalents disjoined randomly. Since no evidence for an interaction between nonhomologous univalent chromosomes which leads to their non-random disjunction to opposite poles was found in this study, these data confirm my earlier conclusion (Weber, 1966, 1969) that “distributive pairing does not occur in maize (and probably most other plants) or that it occurs with a much lower efficiency than in Drosophila females”. The frequent “pairing” between nonhomologous chromosomes at diakinesis and metaphase I and the non-random distribution at anaphase I in doubly trisomic maize plants reported by Michel and Burnham (1969) was found neither in my earlier studies (Weber, 1966, 1969) nor in the present study. The current study is far more sensitive than any of the previous studies because two nonhomologous chromosomes lacking pairing partners are found in every cell of a doubly monosomic plant.

Studies of heterosis, combining ability and inheritance of yield and yield components in a diallel cross of bengal gram (Cicer arietinum L.).

Abstract: A 5 X 5 diallel cross among well-adapted varieties of gram from different agroclimatic regions was studied for heterosis, combining ability and inheritance of days-to-flowering, primary branches, pods per plant, 100-seed weight and grain yield. A high degree of heterosis over mid-parent and better parent was observed for primary branches, no. of pods and grain yield, whereas very little heterosis was exhibited for days-to-flower and 100-seed weight. Crosses among lines of diverse origin generally gave higher heterosis and over-dominance than lines from the same region. Primary branch number, pod number, and grain yield exhibited positive over-dominance; days-to-flower showed negative over-dominance while 100-seed weight had no dominance. Both general and specific combining ability effects were significant for all the characters studied but g.c.a. effects appeared to be more important for days-to-flower, 100-seed weight and grain yield. Graphical analysis indicated additive effects for all the characters, with complete dominance for days-to-flower, no dominance for 100-seed weight and over-dominance for the other three characters. Dominant genes conditioned earliness, primary branch number and 100-seed weight. The role of various parents and crosses in planning a hybridization programme has been discussed.

Unstable mutants of bronze induced by pre-meiotic X-ray treatment in maize.

Abstract: A study was made of the effects of pre-meiotic x-irradiation on the bronze locus in chromosome 9 of maize. Plants of Sh Bz Wx/Sh Bz Wx constitution were treated with ca. 1000r and pollen from these individuals was applied to silks of sh bz wx tester plants. In the F1 progeny, three Sh Wx kernels having a bz aleurone or showing Bz-bz variegation (the bz-x3, bz-x4 and bz-x5 mutants) were selected as possible mutations at the bz locus. One kernel of sh bz wx phenotype as well as one exhibiting sh, bz and Wx (sh-bz-x3) were also selected for more intensive study. Progeny tests of the sh bz wx individual along with cytological observations indicated that a ring chromosome was the probable cause of the mutant phenotype although an alternative hypothesis is not ruled out. The behavior of sh-bz-x3 can be interpreted as the result of either a minute deficiency involving the Sh and Bz loci or a simultaneous suppression of the two dominant alleles. Progeny of the bz-x mutants exhibited genetic instability of bronze. It is hypothesized that this behavior is due to the activation or alteration by x-rays of gene control mechanisms which affect the bronze gene.

Somatic association of telocentric chromosomes carrying homologous centromeres in common wheat.

Abstract: Measurements of distances between telocentric chromosomes, either homologous or representing the opposite arms of a metacentric chromosome (complementary telocentrics), were made at metaphase in root tip cells of common wheat carrying two homologous pairs of complementary telocentrics of chromosome 1 B or 6 B (double ditelosomic 1 B or 6 B). The aim was to elucidate the relative locations of the telocentric chromosomes within the cell. The data obtained strongly suggest that all four telocentrics of chromosome 1 B or 6 B are spacially and simultaneously co-associated. In plants carrying two complementary (6 B S and 6 B L) and a non-related (5 B L) telocentric, only the complementary chromosomes were found to be somatically associated. It is thought, therefore, that the somatic association of chromosomes may involve more than two chromosomes in the same association and, since complementary telocentrics are as much associated as homologous, that the homology between centromeres (probably the only homologous region that exists between complementary telocentrics) is a very important condition for somatic association of chromosomes. The spacial arrangement of chromosomes was studied at anaphase and prophase and the polar orientation of chromosomes at prophase was found to resemble anaphase orientation. This was taken as good evidence for the maintenance of the chromosome arrangement — the Rabl orientation — and of the peripheral location of the centromere and its association with the nuclear membrane. Within this general arrangement homologous telocentric chromosomes were frequently seen to have their centromeres associated or directed towards each other. The role of the centromere in somatic association as a spindle fibre attachment and chromosome binder is discussed. It is suggested that for non-homologous chromosomes to become associated in root tips, the only requirement needed should be the homology of centromeres such as exists between complementary telocentrics, or, as a possible alternative, common repeated sequences of DNA molecules around the centromere region.

B chromosome selection in rye.

Abstract: As a consequence of selection the distribution and frequency of B chromosomes varies among survivors of rye seedlings planted in different environments. The mean B frequency per plant decreased under conditions of “high” as compared with “low” density of planting. Differences in weather and soil type between two sites also caused a significant shift in the distribution and frequency of B chromosomes.

The genetics of resistance to long-term exposure to CO2 in Drosophila melanogaster; an environmental stress leading to anoxia.

Abstract: Genetic heterogeneity in populations of D. melanogaster has been described for resistance to long-term exposure to CO2 (4 to 5 hours). Crosses between inbred strains, and between strains set up from single inseminated females collected in the wild show the importance of additive genes. Genetic activity for resistance and sensitivity was found on the X, 2 and 3 chromosomes.

Untersuchungen zur Pollenentwicklung und Pollenschlauchbildung bei höheren Pflanzen

Abstract: In reifen Pollenkornern der beiden Sommergerstensorten Amsel und Wisa sowie der F1-Pflanzen, die aus den Sorten-Kreuzungen Impala X Wisa und Union X Wisa hervorgegangen sind, wurde die DNS-Menge der Kerne cytophotometrisch bestimmt. Die Messungen wurden zugleich bei Spermakernen und vegetativen Kernen eines Pollenkorns vorgenommen. Auserdem wurde der DNS-Gehalt von Kernen von Wurzelspitzen-Zellen der Sorten Amsel und Wisa ermittelt.

Instability of the maize B chromosome.

Abstract: The B 9 chromosome of maize exhibits a very ordered type of instability at the second pollen mitosis, when nondisjunction may reach a level of 95%. Much less commonly the chromosome is unstable during early development of the kernel. Instability in the kernel produces recessive sectors in either the endosperm or the sporophyte, reflecting the absence of dominant markers carried by the B 9. The causes of B 9 loss in the endosperm and the sporophyte were investigated for the two observable classes of sectoring: fractional loss (single event) and multiple loss (mosaic pattern). The fractional class represents isochromosome formation by the B 9 (Carlson, 1970, 1971). Data presented here suggest that the isochromosome is a by-product of telocentric formation at the second pollen mitosis, and does not arise directly from the B 9 chromosome. The chromosomal basis for the mosaic pattern of B 9 loss is not completely known. However, one class of mosaic kernels displays a heritable instability of the B 9 chromosome which apparently results from ring chromosome formation by the B 9. The time of origin of the ring B 9 chromosome is prior to the second pollen mitosis, since the unstable chromosome generated in the male parent is transmitted to both the endosperm and the sporophyte. Finally, a genetic factor controlling B 9 stability in the developing endosperm has been found. A single plant (1818-1), crossed as a female parent to a B 9-containing stock, induced a mosaic pattern of B 9 loss in the endosperm at a very high rate. The characteristics of this plant are being investigated.

Multivariate statistical analysis of grain yield and agronomic characters in Durum wheat.

Abstract: Correlation, stepwise multiple regression and factor analyses were conducted on grain yield and a number of agronomic characters in the parental, F1 and F2 families originating from a 10 X 10 diallel cross in durum wheat. For the F1 diallel, the correlation analysis indicated that the number of spikes and kernels per plant and 1,000 kernel weight had the highest correlations with grain yield; for the F2 diallel, the number of spikes and kernels per meter, 1000 kernel weight and plant height showed most striking correlations with same.

Autotetraploid gene segregation.

Abstract: Autotetraploid gene segregation was studied in Zea mays L. using a marking system of two very closely linked genes (A1 and Sh2) in the repulsion phase. This system makes it possible to identify many euploid and aneuploid genotypes and enables the estimation of some parameters of autotetraploid gene segregation such as double reduction, numerical nondisjunction, and the relative transmission frequencies of monosomic, disomic, and trisomic gametes. It was found that these three types of gametes did not function at the same rates on the male and female sides. Differences in observed segregation ratios between reciprocal testcrosses were explained by this phenomenon. Estimates of the frequency of double reduction were made for loci used after eliminating the effect of numerical non-disjuction on the segregation ratios. The value of double reduction appears to be the same in the male and female tetrasomic tetraploid. Tetraploids which were disomic for chromosome 3 were not isolated although they might be expected to be common in the progeny of self-fertilized or sib-crossed trisomic tetraploids. Their absence may be explained in part by the low rate of transmission of monosomic gametes from the male parent. Autotetraploid populations which are unstable for chromosome number probably achieve an equilibrium between forces which produce aneuploidy and forces which remove aneuploids from the population.

Cytogenetic studies in Trifolium Spp. related to berseem : I. Intra- and interspecific hybrid seed formation.

Abstract: In a cytogenetic study of five annual Trifolium spp. the genetical relationships between (1) T. scutatum Boiss. and (2) T. plebeium Boiss., and between them and (3) T. carmeli Boiss., (4) T. echinatum M. B. and (5) T. latinum Seb., were studied in intra- and interspecific F1 and F2 hybrids. Germination, seedlings development, pollen fertility and chromosome configurations during meiosis and seedset were recorded. All the T. scutatum x T. plebeium F1 were green, but the hybrids between either T. plebeium or T. scutatum and T. carmeli, T. echinatum or T. latinum were mainly albinos. Those that were green had a very high rate of mortality and the survivors produced many albino seedlings. Pollen fertility was about 60% in scutatum x plebeium F1s, and one of their eight bivalents was heteromorphic. Hybrids between either of these and T. carmeli, T. echinatum or T. latinum had 30–50% stainable pollen and had several multivalents, suggesting the existence of a system of chromosomal translocations in these species. Seed set was roughly correlated with pollen stainability. The nature of the isolation mechanisms operating between these species is discussed.