Cytoplasmic Lines Research Articles

Comparison on the Biochemical Characteristics between Alfalfa Sterile Line and Maintainer Line

To study on the morphological character of cytology and physiological and biochemical mechanism of alfalfa cytoplasmic male sterile line, this paper took sterile line MS-GN1A and maintainer line MS-GN1B as raw material, separately conducted microscopic observation to anther in different development stage and determined the content of soluble sugar, starch, soluble protein, free proline and malondialdehyde, and the activity of antioxidant enzyme (catalase, peroxidase and superoxide dismutase). The results showed that: 1. Compared with maintainer line, the pollen grain of alfalfa cytoplasmic male sterile line presented shriveled appearance, smaller size with deletion and few; during the tetrad period of pollen, tapetum cell abnormally grew; callose and epidermis didn’t disintegrate and couldn’t release pollen grain; pollen abortion of alfalfa cytoplasmic sterile line was related to the abnormal development of connective vascular bundle. 2. With the growth and development of bud and the development and maturity of pollen, the content of soluble sugar, starch, soluble protein, and free proline showed deficient phenomenon in each development period of bud of sterile line MS-GN1A; as peroxidation index of membranous substance, the activity of malondialdehyde and antioxidant enzyme was higher than it of homotype maintainer line MS-GN1B.

Mechanisms of Drug Binding to Voltage-Gated Sodium Channels.

Voltage-gated sodium (Na+) channels are expressed in virtually all electrically excitable tissues and are essential for muscle contraction and the conduction of impulses within the peripheral and central nervous systems. Genetic disorders that disrupt the function of these channels produce an array of Na+ channelopathies resulting in neuronal impairment, chronic pain, neuromuscular pathologies, and cardiac arrhythmias. Because of their importance to the conduction of electrical signals, Na+ channels are the target of a wide variety of local anesthetic, antiarrhythmic, anticonvulsant, and antidepressant drugs. The voltage-gated family of Na+ channels is composed of α-subunits that encode for the voltage sensor domains and the Na+-selective permeation pore. In vivo, Na+ channel α-subunits are associated with one or more accessory β-subunits (β1-β4) that regulate gating properties, trafficking, and cell-surface expression of the channels. The permeation pore of Na+ channels is divided in two parts: the outer mouth of the pore is the site of the ion selectivity filter, while the inner cytoplasmic pore serves as the channel activation gate. The cytoplasmic lining of the permeation pore is formed by the S6 segments that include highly conserved aromatic amino acids important for drug binding. These residues are believed to undergo voltage-dependent conformational changes that alter drug binding as the channels cycle through the closed, open, and inactivated states. The purpose of this chapter is to broadly review the mechanisms of Na+ channel gating and the models used to describe drug binding and Na+ channel inhibition.

Retrospective and perspective on <italic>indica</italic> three-line hybrid rice breeding research in China

China’s first indica hybrid rice technology has opened up new methods to substantially increase rice yield, tremendously contributing to China’s food security. In this article, we review the discovery of wild abortive male sterility in rice and the history of the development and combination of the male sterile line, maintainer line and restorer line (the “three-line”). With regards to China’s large-scale application of cytoplasmic-nuclear male-sterile (CMS) lines, in addition to the wild-abortive CMS line, there are also Gang, D, Yinshui, dwarf-abortive, Honglian and K types, of which, only the Honglian type exhibits a different restoring and maintaining relationship from that of the wild-abortive line. The diversity of cytoplasmic sterile lines of hybrid rice solves the potential risk in production caused by the use of a single cytoplasmic line. With respect to the breeding of elite parents, the breeding and application of fine male sterile lines, such as Zhenshan 97A, V20A, II-32A and Jin 23A, and fine restorer lines, such as IR24, Minghui 63 and Shuhui 527, were introduced. Currently, the major varieties of China’s three-line hybrid rice have transformed from the high-yielding varieties in the past into the current high-quality, high-yield and disease-resistant varieties. However, three-line hybrid rice faces several problems, such as slow increases of yield potential, low efficiency in genetic improvement of maintainers, the high cost of hybrid rice seed production and the lack of adaptability to the simplified cultivation method. To meet these challenges, it is recommended to establish objectives of breeding new hybrid rice varieties with high quality, high yield, high safety and high efficiency by applying molecular tools to hybrid rice breeding and developing “three-line” hybrid rice parents suitable for mechanized seed production. These would significantly enhance the technological competitiveness of hybrid rice.

CHARACTERIZATION OF SOME RICE GENOTYPES FOR FERTILITY RESTORING GENES USING RAPD AND SSR MARKERS

With the objective of identifying restorers and maintainers, to identify fertility restoration linked markers that can distinguish cytoplasmic sources and restorer lines, four male sterile and fertile counterparts of Cytoplasmic Male Sterile (CMS) lines and 10 Restorers (R) lines were characterized. Based on spikelet fertility percentages, ten suggested restorer were identified. Giza 182, Giza 178 and Giza 181 were identified as restorers for the CMS lines G46A and D297A. Ten SSR and 12 RAPD markers were used for the identification of the fertility restoration gene in restorer lines. Among ten suggested restorer lines, only three Egyptian rice cultivars, Giza 182, Giza 178 and Giza 181 used in molecular analysis. Two out of ten SSR markers (RM493 and RM510) could differentiate the CMS line, restorer and their hybrids. RM493 produced bands with size of 123, 128 and 126 bp in the restorer cultivars Giza 181, Giza 182 and Giza 178, respectively. Whereas, the SSR marker RM510 produced bands with size of 165, 186 and 162 bp in the restorer cultivars Giza 181, Giza 182 and Giza 178, respectively. These specific markers were found in their corresponding hybrids with CMS line G46A. In addition, two RAPD primers OPK08 and OPK10 produced fertility restoration linked markers with the molecular size of 200 and 690 bp, respectively. These markers were found only in the restorer cultivars and their respective hybrids with the CMS line G46A. The results suggested effective utilization of SSR and RAPD markers in hybrid testing and marker aided heterosis breeding in rice.

Subcellular localisations of the CPTI collection of YFP-tagged proteins in Drosophila embryos.

A key challenge in the post-genomic area is to identify the function of the genes discovered, with many still uncharacterised in all metazoans. A first step is transcription pattern characterisation, for which we now have near whole-genome coverage in Drosophila. However, we have much more limited information about the expression and subcellular localisation of the corresponding proteins. The Cambridge Protein Trap Consortium generated, via piggyBac transposition, over 600 novel YFP-trap proteins tagging just under 400 Drosophila loci. Here, we characterise the subcellular localisations and expression patterns of these insertions, called the CPTI lines, in Drosophila embryos. We have systematically analysed subcellular localisations at cellularisation (stage 5) and recorded expression patterns at stage 5, at mid-embryogenesis (stage 11) and at late embryogenesis (stages 15-17). At stage 5, 31% of the nuclear lines (41) and 26% of the cytoplasmic lines (67) show discrete localisations that provide clues on the function of the protein and markers for organelles or regions, including nucleoli, the nuclear envelope, nuclear speckles, centrosomes, mitochondria, the endoplasmic reticulum, Golgi, lysosomes and peroxisomes. We characterised the membranous/cortical lines (102) throughout stage 5 to 10 during epithelial morphogenesis, documenting their apico-basal position and identifying those secreted in the extracellular space. We identified the tricellular vertices as a specialized membrane domain marked by the integral membrane protein Sidekick. Finally, we categorised the localisation of the membranous/cortical proteins during cytokinesis.

A battle between genomes in plant male fertility

Analyses of a new male sterility gene from a well-known rice cytoplasmic sterile line reveal inhibition of a nucleus-encoded protein and counteractions by nuclear fertility restorer factors. The existence of these genes in wild rice populations suggests that they may confer selective advantages.

Cytoplasmic line effects for birth weight and preweaning growth traits in the Asturiana de los Valles beef cattle breed

A total of 15,645 records of birth weight (BrW), weaning weight (WW) and average daily gain (ADG) from 6055 cows belonging to 2121 different dam lines were analyzed to quantify the contribution of cytoplasmic line (l) effects to phenotypic variance of preweaning growth traits in a sample of Asturiana de los Valles beef cattle breed. Only dam lines with 2 or more cows having performance records in the database were used. Bayesian estimates were obtained fitting eight different univariate and multivariate models defined depending on the inclusion or not of the permanent maternal environment (c) and the l effects. Univariate models that included both the c and the l effects had the best fit with data (assessed by computing the logarithm of the conditional predictive ordinate; logCPO) for BrW and ADG while for WW this was the case for the model that only included the c effect. For multivariate models, the best fit with data was obtained for the model that only included the c effect (logCPO=−245,899) while the second “better” model was that which only include the l effect value (logCPO=−241,108). In general, whatever the estimation model used, estimates of heritability for the direct (h2) and maternal (m2) genetic effects and the genetic correlation between them (ram) obtained in the current study for BrW were slightly higher (ram more negative) than the most recent estimates reported in the breed. However, this is not true for WW and ADG when multivariate estimation models include the l effect. In these cases, estimates of h2 and m2 for WW and ADG tend to be lower and ram less negative than those previously estimated. In conclusion, the cytoplasmic line may have a marginal effect on growth performance in beef cattle but not sufficient in magnitude to justify including the l effect in models in beef improvement schemes.

A Second infA Plastid Gene Point Mutation Shows a Compensatory Effect on the Expression of the Cytoplasmic Line 2 (CL2) Syndrome in Barley

The IF1 protein is one of the factors controlling translation initiation in bacteria. This protein is encoded by the infA gene, which, in several higher plants, is located in the plastome. Cytoplasmic Line 2 (CL2), an alboviridis barley mutant, was the first to be proposed as an infA gene mutation (T 157 C) in higher plants. This mutant was isolated from a chloroplast mutator genotype (cpm/cpm) and was made genetically stable by backcrosses with a wild-type nuclear genotype. In the present work, genetically stable CL2 plants were backcrossed as females by cpm/cpm plants in order to regain the mutator activity. Interestingly, a seedling carrying a first leaf blade with a darker green stripe on a typical CL2-mutant background was observed in the F(4) generation. The T 157 C transition was confirmed in tissues from the CL2 background, whereas a second transition (A 178 G) was also found in the darker stripe. Two clearly different levels of CL2 syndrome were observed in the seedlings of the F(5) and F(6) progenies. Those of the greener group carried both transitions. These results suggest a compensatory effect of the second mutation and support the involvement of the infA plastid gene in CL2 syndrome, confirming CL2 as the first mutant of this gene reported in higher plants.

Molecular characterization of cytoplasmic male sterility conditioned by Gossypium harknessii cytoplasm (CMS-D2) in upland cotton

Cytoplasmic male sterility (CMS) is a maternally inherited trait that fails to produce functional pollen grains. The CMS system is widely employed to facilitate the utilization of heterosis in major crops. However, little is known about the CMS associated genes in Upland cotton (Gossypium hirsutum). The objective of this study was to compare CMS cotton (CMS-D2) with the cytoplasm from G. harknessii and its isogenic maintainer line with the normal fertile Upland cotton cytoplasm to identify CMS-D2 specific gene(s) and to develop CMS-specific sequence characterized amplified region (SCAR) markers. Based on Southern blot analysis using 10 mitochondrial gene-specific probes (cob, cox2, atp6, atp9, nad3, cox3, atpA, cox1, nad6 and nad9), three probes (cox3, atpA, and nad6) revealed restriction fragment length polymorphisms (RFLP) between the CMS-D2 and its isogenic maintainer line. RT-PCR confirmed that the three genes were differentially expressed between the two lines. These results indicated that there existed structural and expression variations in the three genes when the mitochondrial D2 genome was transferred into Upland cotton. Genome walking and rapid amplification of cDNA ends (RACE) were further performed to analyze the sequences of these genes and their flanking regions. For cox3 and nad6, there was only one different nucleotide each in the gene regions between the two lines. Also some nucleotides upstream of the ATG codon were different. For atpA, the sequences downstream the atpA were significantly different between the two cytoplasmic lines. Furthermore, two nucleotides at the -4 and -5 position from ATG codon were also changed between the two cytoplasms (i.e., CG→AA), and this mutation also exists in RNA sequences. Interestingly, nine nucleotides (ATGCAACTA) were also inserted at the location of 899 bp upstream of ATG codon in the CMS line. The results suggest that the abnormal sequence and expression of atpA gene is associated with CMS expression in Upland cotton. According to the significant different sequences downstream the atpA gene, a CMS-D2 specific SCAR marker was developed. The CMS-specific PCR bands were verified for 10 cultivars containing either normal- or CMS-D2cytoplasm. This will allow quick and reliable identification of the cytoplasmic types of individual plants at the seedling stage, and assessment of the purity of F1 seed lots.

Estimation of genetic parameters and effects of cytoplasmic line on scrotal circumference and semen quality traits in Angus bulls

The purpose of this study was to estimate the heritability of scrotal circumference (SC) and semen traits, genetic correlations between SC and semen quality traits, and the effect of cytoplasmic line on SC and semen traits. Breeding soundness exam (BSE) data were collected on registered Angus bulls at 4 ranches over 7 yr. The American Angus Association provided historical pedigree information to estimate the effect of cytoplasmic line on SC and semen quality traits. After editing, the evaluated data set contained 1,281 bulls with breeding soundness exam data that traced back to 100 founder dams. Data were analyzed using a 2-trait animal model to obtain heritability, genetic correlation between SC and semen quality traits, as well as the effect of cytoplasmic line as a random effect for SC, percent motility (MOT), percent primary abnormalities (PRIM), percent secondary abnormalities (SEC), and percent total abnormalities (TOT) using multiple-trait derivative-free REML. Fixed effects included source ranch and collection year, and test age was used as a covariate. Estimates of heritability for SC, MOT, PRIM, SEC, and TOT were 0.46, 0.05, 0.27, 0.23, and 0.25, respectively. Genetic correlations between SC and MOT, PRIM, SEC, and TOT were 0.36, -0.19, -0.11, and -0.23, respectively. The proportions of phenotypic variance accounted for by cytoplasmic line for SC, MOT, PRIM, SEC, and TOT were <0.001, 0.013, 0.023, 0.002, and <0.001, respectively. Genetic correlations between SC and semen quality traits were low to moderate and favorable. Cytoplasmic line may have a marginal effect on MOT and PRIM, but is likely not a significant source of variation for SC, SEC, or TOT.

RFLP analysis of mitochondrial DNA in two cytoplasmic male sterility systems (CMS-D2 and CMS-D8) of cotton

Cytoplasmic male sterility (CMS) in higher plants is a maternally inherited trait and CMS-associated genes are known to be located in the mitochondrial genome. However, CMS-inducing genes in CMS-D2 and CMS-D8 of Upland cotton (Gossypium hirsutum L., AD1) are currently unknown. The objective of this study was to identify potential candidate DNA or gene sequences for CMS-D2 and CMS-D8 through restriction fragment length polymorphism (RFLP) analysis. Seven mtDNA gene probes and five restriction enzymes were first used to compare D2 (from G. harknessii Brandegee) and AD1 cytoplasms. With cox1, cox2, and atp1 as probes, RFLP polymorphisms were detected with one or more restriction enzyme digestions. The most notable difference was an additional fragment in the normal AD1 cytoplasm detected by cox2 in digests of three enzymes, and by cox1 and atp1 in digests with PstI. The RFLP analysis was then conducted among CMS-D2, CMS-D8 (from G. trilobum (DC.) Skovst.), and AD1 cytoplasms. Two probes from maize, atp1 and atp6, detected polymorphism among the different cytoplasmic lines. However, no difference in RFLP patterns was noted between male sterile (A) and restorer (R) lines with the D2 or D8 cytoplasm, indicating that the presence of the D2 or D8 restorer gene does not affect mtDNA organization in Upland cotton. The results demonstrate that RFLP using atp1 and atp6 as probes can distinguish the three cytoplasms. The atp1 and atp6 in CMS-D8 and these two genes together with cox1 and cox2 in CMS-D2 could be the candidates of CMS-associated genes in the mitochondrial genome, providing information for further molecular studies and developing PCR-based markers for the CMS cytoplasms in breeding. This research represents the first work using RFLP to analyze the genetic basis of CMS in cotton.

A Cytoplasmically Inherited Barley Mutant Is Defective in Photosystem I Assembly Due to a Temperature-Sensitive Defect in ycf3 Splicing

A cytoplasmically inherited chlorophyll-deficient mutant of barley (Hordeum vulgare) termed cytoplasmic line 3 (CL3), displaying a viridis (homogeneously light-green colored) phenotype, has been previously shown to be affected by elevated temperatures. In this article, biochemical, biophysical, and molecular approaches were used to study the CL3 mutant under different temperature and light conditions. The results lead to the conclusion that an impaired assembly of photosystem I (PSI) under higher temperatures and certain light conditions is the primary cause of the CL3 phenotype. Compromised splicing of ycf3 transcripts, particularly at elevated temperature, resulting from a mutation in a noncoding region (intron 1) in the mutant ycf3 gene results in a defective synthesis of Ycf3, which is a chaperone involved in PSI assembly. The defective PSI assembly causes severe photoinhibition and degradation of PSII.

Applying the genetic theories of ageing to the cytoplasm: cytoplasmic genetic covariation for fitness and lifespan

Two genetic models exist to explain the evolution of ageing - mutation accumulation (MA) and antagonistic pleiotropy (AP). Under MA, a reduced intensity of selection with age results in accumulation of late-acting deleterious mutations. Under AP, late-acting deleterious mutations accumulate because they confer beneficial effects early in life. Recent studies suggest that the mitochondrial genome is a major player in ageing. It therefore seems plausible that the MA and AP models will be relevant to genomes within the cytoplasm. This possibility has not been considered previously. We explore whether patterns of covariation between fitness and ageing across 25 cytoplasmic lines, sampled from a population of Drosophila melanogaster, are consistent with the genetic associations predicted under MA or AP. We find negative covariation for fitness and the rate of ageing, and positive covariation for fitness and lifespan. Notably, the direction of these associations is opposite to that typically predicted under AP.

Development of two new molecular markers specific to cytoplasmic male sterility in tuber mustard (Brassica juncea var. tumida Tsen et Lee)

A novel and stable cytoplasmic male sterility CMS line of tuber mustard has been bred by subsequent backcrosses for 10 years. Two specific markers atpA and orf220 were cloned and partially characterized in our previous study (Zhang et al. 2003). In this study, two new molecular markers, orf256 and orf305/orf324, have been isolated and identified. The orf256 gene size was found to be 825 bp in CMS line and a 1,357 bp in its maintainer line. Sequence analysis indicated that the orf256 gene was an entire coding sequence and downstream of the cox1 gene. Interestingly, the 906 bp fragment, which contains part of the sequence of orf222, nad5 and orf139 genes, was found to be inserted from the 451st bp of 5′-flank of the 1,357 bp fragment. In the same way, the orf324 gene was isolated from CMS line and orf305 gene from its maintainer line. Both of them are entire coding sequences, upstream from nad3 and rps12 gene, and co-transcribed with the nad3 and rps12 genes. In addition, two molecular markers, orf256 and orf324/orf305, have been successfully converted into the SCAR markers. Subsequently, ORF256, ORF324, ORF305 protein and ORF256-M-431 fragment are predicated to contain signal peptide sequences, and ORF220 was predicated to contain signal anchor sequence. RFLP analysis results revealed that all of the molecular markers exhibited polymorphisms. Northern blot analysis indicated that the expression level of these genes in CMS line is higher than that of the maintainer line. In the mass, all of these genes are expressed lower in the leaf than that of floral organs between the CMS line and its maintainer line. The difference in expression pattern of different mitochondrial specific marker genes suggests that the abundance of mitochondrial proteins is differentially regulated in the organ/tissue development in tuber mustard. Results of this study also provide some novel and useful clues to explore the biological function of these specific marker genes in the tuber mustard.

The barley plastome mutant CL2 affects expression of nuclear and chloroplast housekeeping genes in a cell-age dependent manner

The barley plastome mutant CL2 (cytoplasmic line 2) carries a point mutation in the infA gene, a homologue of the bacterial gene for the conserved translation initiator factor 1 (IF1). The function of infA in plastids is not known. The mutation in CL2 leads to a temporal chlorophyll deficiency in the primary leaf blade that is normalised in the basal and middle parts during further development. We have compared the expression of selected nuclear and plastid genes in different parts of primary leaves of CL2 and wild-type and found no indication for an adverse effect of the mutation on plastidial transcription. We observed an enhanced expression of RpoTp (encoding the phage-type nuclear-encoded plastid RNA polymerase) suggested to be caused by retrograde plastid signalling. Decreased amounts of plastid rRNA in basal and top sections are in agreement with the idea that the mutation in infA leads to a time- and position-dependent defect of plastid translation that causes a delay in plastid development. The normalisation of the phenotype in the middle section of CL2 leaves correlates with wild-type levels of chloroplast 16S rRNA and RbcL and increased expression of plastid housekeeping genes. The normalisation was not observed in cells at the tip of CL2 leaves suggesting different ways of regulating chloroplast development in cells at the tip of primary barley leaves as compared with other leaf sections.

Mitochondrial DNA Phylogeny of Cultivated and Wild Beets: Relationships Among Cytoplasmic Male-Sterility-Inducing and Nonsterilizing Cytoplasms

Cytoplasmic male sterility (CMS), the maternally inherited failure to produce functional pollen, has been used in the breeding of sugar beet (Beta vulgaris ssp. vulgaris). At least three different sources of CMS can be distinguished from one another as well as from normal fertile cytoplasm by polymorphisms in their mitochondrial genomes. Here we analyzed 50 accessions of cultivated and wild beets to investigate the phylogenetic relationships among male-sterility-inducing and normal cytoplasms. The haplotypes were characterized by the nucleotide sequence of the mitochondrial cox2-cox1 spacer region and mitochondrial minisatellite loci. The results indicated that (1) a normal cytoplasm line, cv. TK81-O, was situated at the major core node of the haplotype network, and (2) the three sterilizing cytoplasms in question derived independently from the core haplotype. The evolutionary pathway was investigated by physical mapping study of the mitochondrial genome of a wild beet (B. vulgaris ssp. orientalis) accession BGRC56777 which shared the same mitochondrial haplotype with TK81-O, but was not identical to TK81-O for the RFLP profiles of mitochondrial DNA. Interestingly, three sets of inverted repeated sequences appeared to have been involved in a series of recombination events during the course of evolution between the BGRC56777 and the TK81-O mitochondrial genomes.

Two infA Gene Mutations Independently Originated from a Mutator Genotype in Barley

Cytoplasmic line 2 (CL2) is a chlorophyll mutant that was selected from a plastid mutator genotype in barley. The dynamics of greening and plastid development of CL2 first-leaf blade contrasts with that of monocots. Previous characterizations of CL2 suggested that this mutant has a delay of plastid gene translation during embryogenesis. We hypothesize that CL2 is a mutant in the infA gene, which encodes translation initiation factor 1 (IF1). Wild-type barley infA gene differs in some nucleotides from that in wheat, but the corresponding IF1 proteins are identical. However, infA from CL2 carries a point mutation, which leads to an amino acid change in IF1 residue 52. One CL2-like seedling selected from a new mutator pool also carries a point mutation in infA gene, this time leading to a change of the universally conserved amino acid residue 32. Both point mutations were T --> C substitutions. We sequenced the complementary DNA of the infA transcripts from the wild type and CL2 and found that the mutation was conserved at the mRNA level. Results strongly suggest that CL2 and CL2-like are infA gene mutants, this being the first time that a mutant phenotype is attributed to infA gene in a higher plant.

An anther‐specific lipid transfer protein gene in sugar beet: its expression is strongly reduced in male‐sterile plants with Owen cytoplasm

Differential screening of a sugar beet (normal cytoplasm line TK81‐O) cDNA library made with anther tissues of various stages resulted in the isolation of a clone (#74‐29) that hybridized to flower bud RNA but did not hybridize to RNA of vegetative organs. The clone contained an open reading frame (ORF) (designated bvLTP‐1) that encoded a putative lipid transfer protein. We also identified a second copy (bvLTP‐2) of the gene. In situ hybridization analysis demonstrated that expression of bvLTP‐1 was confined to the tapetal cells of the anthers at the young microspore stage. Flower bud RNA was prepared from male‐sterile sugar beet with Owen cytoplasm and fertility‐restored plants and used for northern hybridization with the bvLTP‐1 probe. Interestingly, bvLTP‐1 was found to be expressed in the flower buds from the restored plants producing 30% or more stainable pollen, but not in the flower buds from completely sterile or poorly fertility‐restored plants. These results lead us to suppose that the expression of bvLTP‐1 is strongly reduced in the tapetum in response to mitochondrial dysfunction and subsequent physiological changes caused by the Owen cytoplasm.

Lack of evidence for cytoplasmic effects for four traits of Polypay sheep1

Analyses of birth and weaning weights, fleece weights of ewes, and number born per litter of Polypay sheep collected at the U.S. Sheep Experimental Station from 1978 through 1998, confirmed previous analyses of three other dual-purpose breeds that cytoplasmic effects do not contribute to variation in these four traits. In general, estimates of genetic parameters that would be needed for national genetic evaluation were similar to previous estimates for Columbia, Rambouillet, and Targhee sheep, although estimates of direct heritability for Polypay were somewhat less for birth weight, slightly greater for weaning weight, significantly greater for fleece weight, and the same for number born as for those three breeds. For birth weight only, evidence was found for important dam x year or dam x number born interactions, which are essentially litter effects, as was found for the other dual-purpose breeds. There were 11,896, 11,104, 7,748, and 7,831 records for birth and weaning weights, fleece weight, and number born per litter, with 255 to 316 sires of animals with records. There were 260 and 261 cytoplasmic lines for fleece weight and number born, and 861 and 882 for weaning and birth weights.

Comparison of models including cytoplasmic effects for traits of Rambouillet sheep

The objective was to determine appropriate analytical models considering cytoplasmic inheritance for birth weight (BWT, n=35,604), weaning weight (WWT, n=34,114), fleece weight (FWT, n=38,113) and number born (NB, n=39,029) for Rambouillet sheep. For BWT, models that included dam by year, dam by number born, and sire by dam effects, in addition to direct and maternal effects, were significantly better than the basic maternal effects model. For WWT, variances due to direct, maternal, and maternal permanent environmental effects (0.05 of variance) were not zero. For FWT, heritability was 0.55 for all models, but models with dam by year (0.02), sire by dam (0.05), and sire by cytoplasmic line (0.02) were jointly significantly better than models with permanent environmental effects. For NB, only direct heritability (0.08) and relative permanent environmental variance (0.04) were not zero. No trait showed evidence of variation due to cytoplasmic effects. Adding seldom considered effects to the model did not change estimates of variance due to direct and maternal genetic effects. Variance due to dominance effects may be important for BWT and FWT. The basic direct–maternal effects model seems sufficient for genetic evaluations for WWT and FWT but models for BWT and NB may need to include other effects.