A stably transmitted pair of translocated supernumerary chromosomes in maize

Genome ◽  
1995 ◽  
Vol 38 (3) ◽  
pp. 558-565 ◽  
Author(s):  
Marjorie P. Maguire
Keyword(s):  
Chiasma Formation ◽  
B Chromosome ◽  
Supernumerary Chromosome ◽  
Chromosome Segment ◽  
Crossing Over ◽  
Preferential Pairing ◽  
Supernumerary Chromosomes ◽  
Unknown Source ◽  
Chromosome Segments

A pair of stably transmitted supernumerary chromosomes of unknown source has been found in a maize stock carrying a desynaptic mutant. The presence of the supernumerary chromosome appears to be unrelated to the meiotic mutant, but is believed to have been derived from a translocated B chromosome contaminant. The supernumerary chromosomes carry a segment of a A chromosome in this stock where there appear to be two normal copies of each of the 10 A chromosomes. Thus, this A chromosome segment is present in quadruplicate. Surprisingly, a quadrivalent configuration is formed in most microsporocytes, which involves not only synapsis but also chiasma formation in the A chromosome segments involved in the quadrivalent. This represents a strong preferential pairing of supernumeraries with the normal A chromosome segments. Such nonrandom association and crossing over might provide information on the nature of early homologue alignment at meiosis.Key words: supernumerary chromosomes, modified B chromosome, BA translocation, preferential pairing and crossing over.

The use of linkage disequilibrium to map quantitative trait loci

2005 ◽  
Vol 45 (8) ◽  
pp. 837 ◽  
Author(s):  
M. E. Goddard ◽  
T. H. E. Meuwissen
Keyword(s):  
Linkage Disequilibrium ◽  
Quantitative Trait Loci ◽  
Statistical Model ◽  
Quantitative Trait ◽  
Linear Models ◽  
Chromosome Segment ◽  
Identical By Descent ◽  
Trait Loci ◽  
Linkage Disequilibrium Information ◽  
Chromosome Segments

This paper reviews the causes of linkage disequilibrium and its use in mapping quantitative trait loci. The many causes of linkage disequilibrium can be understood as due to similarity in the coalescence tree of different loci. Consideration of the way this comes about allows us to divide linkage disequilibrium into 2 types: linkage disequilibrium between any 2 loci, even if they are unlinked, caused by variation in the relatedness of pairs of animals; and linkage disequilibrium due to the inheritance of chromosome segments that are identical by descent from a common ancestor. The extent of linkage disequilibrium due to the latter cause can be logically measured by the chromosome segment homozygosity which is the probability that chromosome segments taken at random from the population are identical by descent. This latter cause of linkage disequilibrium allows us to map quantitative trait loci to chromosome regions. The former cause of linkage disequilibrium can cause artefactual quantitative trait loci at any position in the genome. These artefacts can be avoided by fitting the relatedness of animals in the statistical model used to map quantitative trait loci. In the future it may be convenient to estimate this degree of relatedness between individuals from markers covering the whole genome. The statistical model for mapping quantitative trait loci also requires us to estimate the probability that 2 animals share quantitative trait loci alleles at a particular position because they have inherited a chromosome segment containing the quantitative trait loci identical by descent. Current methods to do this all involve approximations. Methods based on concepts of coalescence and chromosome segment homozygosity are useful, but improvements are needed for practical analysis of large datasets. Once these probabilities are estimated they can be used in flexible linear models that conveniently combine linkage and linkage disequilibrium information.

SEX AND SUPERNUMERARY CHROMOSOMES IN THE DIOECIOUS GRASS SOHNSIA FILIFOLIA

1972 ◽  
Vol 14 (1) ◽  
pp. 175-180 ◽  
Author(s):  
D. N. Singh
Keyword(s):  
Sex Determination ◽  
Y Chromosome ◽  
Supernumerary Chromosome ◽  
The Other ◽  
Male Plant ◽  
Diploid Male ◽  
Male And Female ◽  
Supernumerary Chromosomes ◽  
Determination System ◽  
Sex Determination System

A dioecious grass Sohnsia filifolia (Fourn.) Airy Shaw (Syn. Calamochloa filifolia Fourn.) from Mexico has been found to have 2n = 20 chromosomes in both male and female plants. The staminate plants have one chromosome much longer than the other chromosomes of the complement. One pistillate plant was found to have 30 chromosomes, among which the largest chromosome is quite similar to the largest component of the diploid male plant. The longest chromosome has been designated as the Y chromosome. An XY-mechanism of the Drosophilia type has been suggested for the sex determination system in this species. One small supernumerary chromosome was observed in the microsporocytes of some male plants, but was absent in roots.

scholarly journals QTL mapping of grain length in rice (Oryza sativa L.) using chromosome segment substitution lines

2006 ◽  
Vol 88 (2) ◽  
pp. 93-104 ◽  
Author(s):  
JIANKANG WANG ◽  
XIANGYUAN WAN ◽  
JOSE CROSSA ◽  
JONATHAN CROUCH ◽  
JIANFENG WENG ◽  
...  
Keyword(s):  
Qtl Mapping ◽  
Likelihood Ratio ◽  
Likelihood Ratio Test ◽  
Stepwise Regression ◽  
Chromosome Segment ◽  
Ratio Test ◽  
Grain Length ◽  
Donor Parent ◽  
Segment Substitution ◽  
Chromosome Segments

Chromosome segment substitution (CSS) lines have the potential for use in QTL fine mapping and map-based cloning. The standard t-test used in the idealized case that each CSS line has a single segment from the donor parent is not suitable for non-idealized CSS lines carrying several substituted segments from the donor parent. In this study, we present a likelihood ratio test based on stepwise regression (RSTEP-LRT) that can be used for QTL mapping in a population consisting of non-idealized CSS lines. Stepwise regression is used to select the most important segments for the trait of interest, and the likelihood ratio test is used to calculate the LOD score of each chromosome segment. This method is statistically equivalent to the standard t-test with idealized CSS lines. To further improve the power of QTL mapping, a method is proposed to decrease multicollinearity among markers (or chromosome segments). QTL mapping with an example CSS population in rice consisting of 65 non-idealized CSS lines and 82 chromosome segments indicated that a total of 18 segments on eight of the 12 rice chromosomes harboured QTLs affecting grain length under the LOD threshold of 2·5. Three major stable QTLs were detected in all eight environments. Some minor QTLs were not detected in all environments, but they could increase or decrease the grain length constantly. These minor genes are also useful in marker-assisted gene pyramiding.

Can abortive early homologous associations promote increased crossing-over in an adjacent rearranged segment?

Genome ◽  
1988 ◽  
Vol 30 (4) ◽  
pp. 469-472 ◽  
Author(s):  
Marjorie P. Maguire
Keyword(s):  
Crossing Over ◽  
Meiotic Pairing ◽  
Pairing Behavior ◽  
Chromosome Segments

Meiotic pairing behavior of rearranged chromosome segments is compared across an informative series of combinations. The question is raised whether the simplest explanation for some peculiar findings may include a sequence of synaptic precursor events at leptotene or zygotene, the course of which may eventually strongly affect crossover frequency.Key words: meiosis, synapsis, crossing-over, rearrangement.

THE EVOLUTIONARY HISTORY OF DROSOPHILA BUZZATII. XII. THE GENETIC BASIS OF STERILITY IN HYBRIDS BETWEEN D. BUZZATII AND ITS SIBLING D. SERIDO FROM ARGENTINA

Genetics ◽  
1986 ◽  
Vol 114 (3) ◽  
pp. 841-857
Author(s):  
Horacio Naveira ◽  
Antonio Fontdevila
Keyword(s):  
Evolutionary History ◽  
Genetic Basis ◽  
Hybrid Sterility ◽  
Polytene Chromosomes ◽  
Chromosome Segment ◽  
Minimum Size ◽  
Drosophila Buzzatii ◽  
History Of ◽  
Male Hybrid ◽  
Chromosome Segments

ABSTRACT The genetic basis of hybrid sterility has been investigated in backcross segmental hybrids between two sibling species, Drosophila buzzatii and D. serido. Asynapsis of homologous bands in hybrid polytene chromosomes has been used to identify the D. serido chromosome segments introgressed into the D. buzzatti genome. All the investigated chromosomes contain male sterility factors. For autosomes, sterility is produced when an introgressed D. serido chromosome segment, or combination of segments, reaches a minimum size. On the other hand, any introgressed X chromosome segment from D. serido, irrespective of its size, produces either male hybrid sterility or inviability.

B-CHROMOSOME-STIMULATED CROSSING OVER IN MAIZE

Genetics ◽  
1969 ◽  
Vol 63 (3) ◽  
pp. 601-609
Author(s):  
George P Hanson
Keyword(s):  
B Chromosome ◽  
Crossing Over

scholarly journals Sex differences in recombination of linked genes in animals

1967 ◽  
Vol 9 (2) ◽  
pp. 211-220 ◽  
Author(s):  
L. C. Dunn ◽  
Dorothea Bennett
Keyword(s):  
Sex Differences ◽  
House Mouse ◽  
Animal Species ◽  
General Rule ◽  
Chiasma Formation ◽  
Crossing Over ◽  
Lepidopteran Species ◽  
Heterogametic Sex

Reports of sex differences in crossing-over in animals, published since Haldane in 1922 suggested that crossing-over should be less frequent in the heterogametic sex, have been reviewed and discussed. No general rule is discernible apart from the absence of crossing-over in males of the dipteran genera Drosophila and Phryne and in females of some lepidopteran species, due apparently to failure of chiasma formation in the heterogametic sex. In the majority of animal species examined crossing-over occurs in both sexes. While there is some tendency in mammals for crossover values in females to exceed those in males, it was of greater interest to find that marked sex-differences occur in the same species (data chiefly from the house mouse) in opposite directions in different chromosomes. The influence of factors acting locally in the chromosomes, such as those associated with hetero-chromatin, were indicated as promising subjects for the study of variations associated with sex.

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