A. A. Moffett

Bio: A. A. Moffett is an academic researcher. The author has contributed to research in topics: Ploidy. The author has an hindex of 1, co-authored 1 publications receiving 135 citations.

Primary and secondary chromosome balance in Pyrus.

Abstract: 1. The basic chromosome number inPyrus is seventeen. Cultivated varieties are all orthoploid. Aneuploid seedlings are poor and abnormal. 2. The somatic chromosomes in “diploid”Pyrus have four representatives of a long type, in “triploid,” six. 3. Multiple association occurs amongst the chromosomes of “diploid”Pyrus giving, in extreme cases, seven groups; four quadrivalents and three sexivalents (Table I). 4. In “triploid” varieties ofP. Malus associations of four, five, six, seven, eight and nine chromosomes have been observed, although trivalents are usually formed (Table II). This means that antosyndesis takes place within each of the three supposed haploid complements. 5. Instead of giving a binomial frequency or the elimination of intermediate numbers, natural seedlings of “triploid” apples most frequently have numbers of chromosomes approximately to 2n + 7 (Table III). 6. Thus the pairing, morphology, and breeding results show, directly or indirectly, that the thirty-four chromosomes in the “diploid”Pyrus are of seven types, of which four are represented four times and three are represented six times. Such forms may be described as trebly hexasomic tetraploids (v. diagram, p. 145). 7. The number seventeen is therefore a secondary (unbalanced) basic number, and the derived series of polyploids (2n = 34, 51, 68) aresecondary polyploids. 8. The establishment of a secondary basic number must mean (on the analogy of all experimental observations) a definite evolutionary step. It is therefore plausible that thePyrus group owe their special morphological characters (e.g. the pome type of fruit) to this reorganisation of the nucleus. The work is being continued with this consideration in view.

Aligning male and female linkage maps of apple (Malus pumila Mill.) using multi-allelic markers

Abstract: Linkage maps for the apple cultivars ‘Prima’ and ‘Fiesta’ were constructed using RFLP, RAPD, isozyme, AFLP, SCAR and microsatellite markers in a ‘Prima’בFiesta’ progeny of 152 individuals. Seventeen linkage groups, putatively corresponding to the seventeen haploid apple chromosomes, were obtained for each parent. These maps were aligned using 67 multi-allelic markers that were heterozygous in both parents. A large number of duplicate RFLP loci was observed and, in several instances, linked RFLP markers in one linkage group showed corresponding linkage in another linkage group. Distorted segregation was observed mainly in two regions of the genome, especially in the male parent alleles. Map positions were provided for resistance genes to scab and rosy leaf curling aphid (Vf and Sd 1, respectively) for the fruit acidity gene Ma and for the self-incompatibility locus S. The high marker density and large number of mapped codominant RFLPs and some microsatellite markers make this map an ideal reference map for use in other progenies also and a valuable tool for the mapping of quantitative trait loci.

Genetic Variation in Chromosome Pairing

Abstract: Publisher Summary This chapter discusses the genetic variation in chromosome pairing Alterations in the behavior of chromosomes at meiosis are known to result from genetic variation as well as from differences in several environmental factors The operation of selection on genetically controlled variation in the chromosomal phenotype is responsible for the development of meiotic mechanisms adapted to the requirements of the breeding structures of species and of their populations The fertility of an organism and consequently the fitness of the lineage to which it belongs are intimately related in sexual forms and in some apomicts, to the efficiency of the over-all meiotic process The prime function, upon which the efficacy of the process depends, is the segregation of homologous chromosomes Two distinct aspects of the process of meiotic chromosome pairing are therefore under genetic control The extent to which synapsis is realized within the chromosome complement is determined by the activities of major genes and polygenes and by interactions within the genetic system comprised of relevant genes of both kinds The specificity of synapsis is widened or narrowed by gene action to permit the pairing of chromosomes distantly or closely related genetically and evolutionarily

Systematic and evolutionary implications of rbcL sequence variation in Rosaceae

Abstract: The angiosperm family Rosaceae poses a number of noteworthy systematic problems as well as many questions concerning morphological and chromosomal evolution. Phylogenetic analysis of rbcL gene sequences was performed to address systematic and evolutionary problems of Rosaceae. Both rbcL sequence variation and the presence of duplicated sequences near the 3' end of rbcL were useful in determining phylogenetic relationships in this family. Analyses of rbcL sequences indicate that there are groups of genera within Rosaceae comparable to the subfamilies Maloideae, Amygdaloideae, and Rosoideae, although the composition of each group differs from traditional circumscriptions. According to analysis of rbcL data, Maloideae and Amygdaloideae each include additional taxa not normally associated with them. All members of Rosoideae with x = 9 are phylogenetically well separated from the x = 8 and 7 members of the subfamily. In addition, Spiraeoideae are not monophyletic but appear to consist of several distinct evolutionary lineages. The rbcL-based phylogenies suggest that chromosome numbers are more reliable indicators of some generic alliances than the more commonly used fruit types. Sequence data are also useful in determining the alliances of several problematic genera, suggesting that the capsular and follicular-fruited genera Vauquelinia, Lindleya, and Kageneckia (usually placed in Spiraeoideae) should be included in the pome-fruited subfamily Maloideae, and that Quillaja is not a member of Rosaceae. Molecular data are consistent with several suggestions for the ancestral chromosome numbers and fruit types of Rosaceae, but do not support any one hypothesis for either. This study also suggests that the subfamily Maloideae may have descended from spiraeoid ancestors and that the pome is derived from follicular or capsular fruit types.

Cytological characteristics associated with the different growth habits in the dicotyledons

Abstract: IN REVIEWING the cytology of a number of different families of dicotyledonous angiosperms, the writer noted that although there were no characteristic differences between the chromosomes of the various larger systematic divisions of this subclass, there appeared to be, on the other hand, a definite set of characteristics associated with the different growth habits, particularly the woody plants as opposed to the herbs, and the annual or biennial as distinguished from the perennial species. In order to test this apparent phenomenon, he undertook a systematic review of the chromosomal characteristics of all dicotyledonous genera sufficiently recorded in the literature for this purpose. The results of this survey are recorded in the present paper. MATERIAL AND METHODS.-Three chromosomal characteristics were selected as the easiest to treat in the manner contemplated: (1) the basic chromosome number of a genus, (2) the percentage of polyploid species within a genus, and (3) the absolute size of the chromosomes within the genus. The data for the first two characteristics were obtained chiefly from the lists of Tischler (1931, 1936), while additional information on certain genera was obtained from more recent partial lists and from a few treatments of particular genera. In general, genera included in the classification by basic number and by absolute size are those of which at least five species are known, but unless the known species were fairly uniform in character, they were not admitted to the lists unless a larger number of species was recorded. For classification as to percentage of polyploidy, only those genera were selected of which 30 per cent or more of the species are known cvtologically, but an additional list was compiled including all the genera classified as to basic number. The basic number was considered that which was found, either in itself or in multiples of it, in fourfifths or more of the species of the genus. If a second number occurred in a considerable proportion of the species, the genus was given one-half value under each number, while if there were three, it was given onethird value under each of them. If there were more than 3 numbers in the genus, only the 3 most common ones were recorded. Numbers near to multiples of the lowest basic number were considered to be derived by polyploidy--e.g., if a genus contained the gametic numbers 8 and 17, the latter was considered as a hypertetraploid based on the former. Only those basic haploid numbers actually found in the genus were recorded; the evidence from secondary pairing was disregarded as being not firmly enough established and not recorded in a sufficient number of genera to be of use in a comprehensive survey such