Power of the joint segregation analysis method for testing mixed major-gene and polygene inheritance models of quantitative traits

Understanding the genetic architecture of quantitative traits can greatly assist the design of strategies for their manipulation in plant-breeding programs. For a number of traits, genetic variation can be the result of segregation of a few major genes and many polygenes (minor genes). The joint segregation analysis (JSA) is a maximum-likelihood approach for fitting segregation models through the simultaneous use of phenotypic information from multiple generations. Our objective in this paper was to use computer simulation to quantify the power of the JSA method for testing the mixed-inheritance model for quantitative traits when it was applied to the six basic generations: both parents (P₁ and P₂), F₁, F₂, and both backcross generations (B₁ and B₂) derived from crossing the F₁ to each parent. A total of 1968 genetic model-experiment scenarios were considered in the simulation study to quantify the power of the method. Factors that interacted to influence the power of the JSA method to correctly detect genetic models were: (1) whether there were one or two major genes in combination with polygenes, (2) the heritability of the major genes and polygenes, (3) the level of dispersion of the major genes and polygenes between the two parents, and (4) the number of individuals examined in each generation (population size). The greatest levels of power were observed for the genetic models defined with simple inheritance; e.g., the power was greater than 90% for the one major gene model, regardless of the population size and major-gene heritability. Lower levels of power were observed for the genetic models with complex inheritance (major genes and polygenes), low heritability, small population sizes and a large dispersion of favourable genes among the two parents; e.g., the power was less than 5% for the two major-gene model with a heritability value of 0.3 and population sizes of 100 individuals. The JSA methodology was then applied to a previously studied sorghum data-set to investigate the genetic control of the putative drought resistance-trait osmotic adjustment in three crosses. The previous study concluded that there were two major genes segregating for osmotic adjustment in the three crosses. Application of the JSA method resulted in a change in the proposed genetic model. The presence of the two major genes was confirmed with the addition of an unspecified number of polygenes. Received: 18 August 2000 / Accepted: 9 March 2001     

INHERITANCE OF RESISTANCE TO CYHALOTHRIN IN THE HOUSEFLY (DIPTERA: MUSCIDAE)

Abstract The genetic inheritance of resistance to cyhalothrin in housefly, Musca domstica (L) was investigated.
Reciprocal crosses between susceptible (S) and resistant (R) strains were used to determine the characteristics of resistance. Analysis of probit line from the F₁ generation and F₂ generation obtained by inbreeding the F₁ hybrids indicated that cyhalothrin resistance was controlled by more than one factors and degree of resistance dominance to cyhalothrin was -0.10, indicating cyhalothrin resistance is conferred by incompletely recessive gene(s). The realized heritability of resistance to cyhalothrin cyhalothrin calculated from data collected routinely from laboratory selection was 0.12.     

Fertile transgenic plants obtained from tritordeum inflorescences by tissue electroporation

 Tissue electroporation was applied to a member of the Triticeae family, namely tritordeum (Hordeum chilense Roem.×Triticum turgidum L. Conv. durum), for the generation of fertile transgenic plants. Two transgenic plants were recovered following the treatment of 361 explants of immature inflorescences (although they were subsequently found to result from the same transformation event). The expression of both inserted marker genes (uidA and bar) was confirmed using standard assays, while transgene integration was confirmed using PCR and Southern hybridization analyses. Integration pattern, segregation ratio and the inheritance of transgene expression in T₁ progeny were consistent for the presence of a single transgene locus containing five to ten plasmid insertions. Although this procedure has been applied to other cereal species, stable transformation of the Triticeae using tissue electroporation has not previously been reported. Received: 28 October 1999 / Revision received: 25 August 2000 / Accepted: 29 August 2000     

The inheritance of a wingless character in the 2spot ladybird (Adalia bipunctata)

A viable wingless 2spot ladybirdAdalia bipunctata (L.) was found in the wild. Breeding through four generations revealed that the wingless trait was controlled by a recessive allele which displays variable levels of expression. The wingless ladybird is discussed in relation to its potential as a biocontrol agent. One ladybird also occurred in this stock which is suggestive of a supergene controlling the colour polymorphism in this species.     

Small RNA shuffling between murine sperm and their cytoplasmic droplets during epididymal maturation

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Double-Stranded RNA in Rice

Oryza sativa ) and wild rice (O. rufipogon) tissues. It is detected at every developmental stage, and is transmitted very efficiently to progeny via seeds (more than 98%). The dsRNA is maintained at a constant level (approximately 100 copies/cell) in almost all tissues. However, the number of copies increases about 10-fold when host cells are grown in suspension culture. Complete nucleotide sequences of cultivated rice (temperate japonica rice, cv. Nipponbare, J-dsRNA) and wild rice (W-1714, W-dsRNA) dsRNAs have been determined. Both wild and cultivated rice dsRNAs have a single long open reading frame (ORF) containing the conserved motifs of RNA-dependent RNA polymerase and RNA helicase. The coding strands of both contain a site-specific discontinuity (nick) at nt 1,211 (J-dsRNA) or at nt 1,197 (W-dsRNA) from the 5′ end of their coding strand. Rice dsRNA has several unique properties and can be regarded as a novel RNA replicon. This paper discusses the origin and evolution of the rice dsRNA. Received 23 October 1998/ Accepted in revised form 15 December 1998     

Estimating null allele frequencies at a microsatellite locus in the oystercatcher (Haematopus ostralegus)

A significant heterozygote deficiency was found for microsatellite locus 20H7 among adult breeding birds in four populations of the oystercatcher ( Haematopus ostralegus ). Genotype frequencies at seven other loci were according to Hardy–Weinberg equilibria. Deviations between observed and expected genotype numbers decreased substantially when the data were corrected based on the estimated frequency of a putative null allele at locus 20H7 . However, no null homozygotes were observed in the total sample of 378 individuals. The probability that, because of chance effects, null homozygotes were not represented in the sample ( n =230) from the most intensively studied population (Schiermonnikoog) was estimated to be less than 1%. Parent–offspring comparisons from Schiermonnikoog showed that observed genotype numbers in the offspring were in accordance with expected values based on the estimated frequency of the putative null allele in the population. Moreover, a null homozygote was observed among the nestlings. The combined results indicated that a null allele is present at locus 20H7 in oystercatchers and that the inheritance is according to normal Mendelian segregation. If the absence of null homozygotes among adult animals cannot be ascribed to statistical effects, null homozygotes may suffer a selective disadvantage during the juvenile stage.     

Non-Mendelian Inheritance of Early Maturity in Euplotes crassus

ABSTRACT. This paper reports on a new phenomenon in the ciliated protists: cytoplasmically determined early sexual maturity. Stock MN1 of the marine hypotrich Euplotes crassus matures immediately after conjugation. We analyzed the respective contribuboas of the nucleus and the cytoplasm to the inheritance of this stable condition. A genetic marker, and new methods in E. crassus for cytoplasmic labeling, production of amicronucleates, and induction of selfing were used. Crosses within and among the early mature (EM) variants and late mature (LM) "wild type" lines were done in ovarious combinations. Descendants of EM conjugants continued to be EM, and descendants of LM continued to be LM, regardless of the different experimental approaches used. The results of the crosses clearly show that the clonally stable, variant EM phenotype is transmitted at conjugation in a non-Mendelian manner through the cytoplasmic lineage. The expression of the trait is independent of the micronuclear genome, but the precise site and nature of the hereditary basis is unknown.