Complex Traits

Mulberry (Morus L) is one of the economically important trees that have a long history of extensive cultivation in Asia. Mulberry leaf is the sole food for the silkworm Bombyx mori; hence, the sustainability of the sericulture industry is dependent on the continuous supply of nutritious mulberry leaf. Genetic improvement of mulberry for leaf yield, leaf nutritional contents, and adaptability has great socioeconomical importance because the sericulture is the backbone of rutal economy in several Asian countries. Much effort has been made on germplasm collection, characterization, and varietal development through conventional methods. However, the complexity of important agronomic traits, the substantial lag time between germination and sexual maturity, the absence of inbred lines, and the outbreeding nature of mulberry delay the genetic improvement via conventional breeding techniques. In this postgenomic era, having the next generation sequencing facilities in its fold, it is possible to integrate modern genomic tools with conventional breeding techniques to dissect the complex traits into their individual components to gain better control over them. In mulberry, such efforts are lacking. This paper, therefore, summarizes the current position of genetic and genomics research in mulberry and discusses the directions for future research, utilizing the emerging technologies in molecular markers, association genetics, quantitative trait locus mapping, transcriptomics, metabolomics, marker-assisted selection breeding, and transgenesis.

To understand the genetic epidemiology of obesity and cancer means to consider the genetics of not only these two complex diseases but also the many risk factors associated with them and the molecular mechanisms likely to contribute to their underlying etiology. It is therefore the purpose of this chapter to highlight the following: genetic mapping studies that have been done to isolate genes related to obesity, genetic studies aimed to identify genes for obesity risk factors, and, finally, a discussion of the genes shared across or among the studies of obesity and/or its risk factors and the various cancers. This is by no means an exhaustive discussion as these are each complex traits with complex molecular mechanisms. It is, however, intended to be an overview of the genes likely to be involved in the cascade of pathways linking obesity and cancer. It is well known that obesity continues to be a leading public health concern not only in the United States but now worldwide. From 1980 to 2002, the prevalence of obesity doubled in adults aged over 20 and overweight prevalence tripled in children and adolescents aged 6–9 years. The estimates of overweight and obesity in 2003–2004 showed that 17.1% of US children and adolescents were overweight and 32.2% of adults were obese [143]. The increasing rates of obesity among children are especially alarming and suggest continuing increases in the rates of obesity-related cancers. Since being overweight in childhood predicts obesity in adulthood [208], obesity occurring in childhood may operate as a ‘cumulative’ exposure that influences cancer risk in later life. Obese children may be subject to potentially long periods of hormonal exposures that operate during adolescence to influence propensity to neoplastic diseases. In females, childhood obesity may also affect the levels of sex hormone at adolescence. A prospective study of 55-year follow-up on 508 adolescents at 13–18 years from Harvard Growth Study showed that overweight adolescent boys had a nine-fold increased risk of colorectal cancer mortality [161]. Associations between adolescent weight and cancer persisted even after adjusting for adult BMI. A 50-year follow-up of >2,000 British children showed an overall 9% increase in cancer incidence per standard deviation increase in BMI, with effects three times larger for smoking-related cancers. There is also evidence from an Israeli case–control study which indicated that being in the upper quartile of BMI at age 18 years was associated with a 42% increase for ovarian cancer [24]. However, the mechanisms underlying the association between childhood obesity and cancer are not well understood, particularly in conjunction with genetic data. In one case–control study of 40 obese and 40 non-obese prepubertal children, the obese group showed higher levels of IGF-1, insulin, and lower sex-binding hormone than that of the non-obese group [182]. This suggests that high levels of growth factors and altered sex hormone profiles are present in obese children and the exposures to an adverse metabolic milieu may begin early in life.

Mulberry (Morus L) is one of the economically important trees that have a long history of extensive cultivation in Asia. Mulberry leaf is the sole food for the silkworm Bombyx mori; hence, the sustainability of the sericulture industry is dependent on the continuous supply of nutritious mulberry leaf. Genetic improvement of mulberry for leaf yield, leaf nutritional contents, and adaptability has great socioeconomical importance because the sericulture is the backbone of rutal economy in several Asian countries. Much effort has been made on germplasm collection, characterization, and varietal development through conventional methods. However, the complexity of important agronomic traits, the substantial lag time between germination and sexual maturity, the absence of inbred lines, and the outbreeding nature of mulberry delay the genetic improvement via conventional breeding techniques. In this postgenomic era, having the next generation sequencing facilities in its fold, it is possible to integrate modern genomic tools with conventional breeding techniques to dissect the complex traits into their individual components to gain better control over them. In mulberry, such efforts are lacking. This paper, therefore, summarizes the current position of genetic and genomics research in mulberry and discusses the directions for future research, utilizing the emerging technologies in molecular markers, association genetics, quantitative trait locus mapping, transcriptomics, metabolomics, marker-assisted selection breeding, and transgenesis.

We have constructed a 1736-locus maize genome map containing1156 loci probed by cDNAs, 545 probed by random genomic clones, 16 by simple sequence repeats (SSRs), 14 by isozymes, and 5 by anonymous clones. Sequence information is available for 56% of the loci with 66% of the sequenced loci assigned functions. A total of 596 new ESTs were mapped from a B73 library of 5-wk-old shoots. The map contains 237 loci probed by barley, oat, wheat, rice, or tripsacum clones, which serve as grass genome reference points in comparisons between maize and other grass maps. Ninety core markers selected for low copy number, high polymorphism, and even spacing along the chromosome delineate the 100 bins on the map. The average bin size is 17 cM. Use of bin assignments enables comparison among different maize mapping populations and experiments including those involving cytogenetic stocks, mutants, or quantitative trait loci. Integration of nonmaize markers in the map extends the resources available fo...

Assortative mating, or the tendency for individuals with similar phenotypes to mate more frequently than expected by chance, has been reported for a variety of complex traits, including many neuropsychiatric disorders. Although assortative mating has been reported in affective disorders, the studies done to date have been inconclusive. This study attempts to assess the degree of assortative mating in individuals

Androgenic responses of 10 F1 wheat hybrids and 13 parental genotypes were studied. It was observed that the studied androgenic traits (androgenic capacity, callus yield, and frequency of green plants) were genotype dependent. On average for all genotypes, 10.6% of the anthers were responsive and 12.2 calluses were produced per 100 anthers. Line 9D-27-262 and the hybrid 9D-27-262/Posavka-2, had the highest frequencies of green plants, 11% and 12% respectively. It was found that 30.4% of the genotypes produced 2 or more green plants per 100 anthers, which can be considered as sufficient number for use in breeding. Heterotic effects as well as additive and dominant gene actions were found to control the inheritance of all characters.