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Review of genetics in the United States with emphasis on the prenatal, metabolic, genetic counseling, and training aspects of the field.
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Fish genetics has made major strides during the past 20 yr due both to improvements in the ability of fish culturists to manage reproduction and to deliberate experimentation and application. The general finding has been that the quantitative genetics of fish differ little from those of other animals and that the applications of animal improvement techniques are similar for fish and other animals. In addition, a number of novel techniques, such as ploidy manipulation and sex reversal, are relatively easy to achieve with a number of fish species. As a result, some very specialized approaches to research have been possible, and applications to fish production seem to be limited only to the imagination of the breeder. However, only limited application has occurred over a major portion of the industry, and genetic improvement of stocks has been achieved in very few instances. The reason for this apparent dichotomy between opportunity and reality seems to be related to the industry's lack of emphasis on genetic improvement.
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The potential for genetic improvement of reproductive performance in pigs is great. Improvement can be achieved by increased commercial use of F1 hybrid females produced by crossing lines with excellent reproductive performance and by selection within nucleus populations of these lines for improved reproduction as well a for growth and carcass characteristics. The value of incorporating reproductive traits in selection programs is critically dependent on the relative economic values of fat (or lean) and of extra pigs produced. There is widespread agreement that litter size is the first choice as both the selection objective and the criterion to improve reproductive performance, on economic, genetic, and ease of measurement grounds. Although there are few examples of successful response to selection for increased litter size in pigs (exceptions being the University of Nebraska selection experiment and results achieved by hyperprolific selection schemes), overall results do not suggest that selection for litter size is impossible, only that it is difficult with limited resources. Artificial insemination is being used increasingly by pig breeding companies to accelerate rates of genetic improvement and to improve dissemination. Combining data from genetically connected herds and analyzing with BLUP computer programs to make efficient use of information on relatives makes selection for litter size feasible while maintaining selection pressure for growth and carcass traits. Although selection for lifetime productivity is impractical today, the knowledge and data accumulated from successful breeding programs for litter size may help make it the selection objective of the future. Meanwhile, the search continues for useful indirect criteria for selection, from testis size to molecular markers, and scientists are working with highly prolific breeds of Chinese pigs to better understand the physiologic and genetic basis of large litter size.
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A revival of interest in Haldane's equilibrium theory for X-linked lethals has been stimulated by the introduction of accurate tests for the detection of female heterozygotes in Lesch-Nyhan disease. Application of these tests appears to indicate an excess of familial cases. This excess can be attributed to ascertainment bias, a difference in female and male mutation rates, genetic drift, and reproductive compensation. Reproductive compensation will be particularly effective in increasing the proportion of familial cases if (1) birth control is widespread; (2) selection against affected males acts in utero; (3) affected sons show symptoms at an early age; and (4) sons are more highly valued than daughters. We demonstrate how only a few generations of reproductive compensation are sufficient to achieve an approximate equilibrium between selection and mutation showing a high proportion of familial cases. We also discuss the random fluctuations around equilibrium caused by genetic drift.
Public fascination with genetics and the new reproductive technologies seem ubiquitious. Although interest in genetic causation for diseases is not new, attention is increasing. There are several predictable reasons for this. One is the overall decrease in deaths due to infection. As a result, genetic factors producing birth defects loom relatively larger. This is also coupled with the public's increased desire for the ideal pregnancy, especially given a decreased population rate. Finally, the public's appetite is whetted by the increasing number of heritable diseases whose molecular basis is being elucidated. We shall focus on three general areas in which genetic technology increasingly impacts upon the obstetrician/gynecologist: genetics of pregnancy losses, genetics of sex determination and the common gynecologic disorders, and finally prenatal genetic diagnosis, particularly in preimplantation genetics and recovering fetal cells from maternal blood. Most of these topics are discussed in a recent text, where extensive references are available.
Investigations into the genetic basis of reproductive barriers among recognized and putative varieties in Phacelia dubia have provided evidence that even among closely related taxa, multiple pathways can lead to reproductive isolation. A nuclear-based reproductive barrier, expressed as partial hybrid sterility of both pollen and ovules, isolated each pair of recognized varieties. There was no evidence of pre- or post-fertilization barriers; all reproductive barriers were manifested as hybrid gametic sterility. Reproductive relationships of two putative varieties were studied to examine the early stages of reproductive isolation in this group. Both putative varieties exhibited partial reproductive isolation from the recognized varieties in spite of their lack of morphological differentiation from recognized varieties. The barrier isolating one putative variety was similar to the barrier among recognized varieties. The second putative variety and a recognized variety were partially isolated by a unidirectional, nuclear-cytoplasmic barrier that reduced only pollen fertility. The nuclear-cytoplasmic barrier suggested a new application of Haldane's rule.
Significant genetic variation exists within and between breeds of beef cattle for age at puberty (AP). In general, faster-gaining breed groups of larger mature size reach puberty at a later age than do slower-gaining breed groups of smaller mature size; breeds selected for milk production reach puberty at younger ages than do those breeds not selected for milk production. Heterosis, independent of heterosis effects on weight, influences most measures of puberty in females and scrotal circumference (SC) in males. Crossbred heifers reach puberty at younger ages and heavier weights than their straightbred counterparts. Scrotal circumference has been shown to be an excellent indicator of AP in yearling bulls. Furthermore, a favorable genetic relationship exists between SC in bulls and AP of female offspring. Beef cattle breeders may take a direct approach to breeding for AP and subsequent reproduction by directly selecting for measures of fertility such as SC. However, an indirect approach, involving selection for an array of traits that provide an appropriate "genetic environment" for the expression of fertility (i.e., size, milk production, calving ease) may be preferred. Although seedstock producers are limited to making change through within-breed selection, commercial producers can take advantage of both within- and between-breed selection as well as crossbreeding to achieve the same goal.
Over the past four decades, reproductive biotechnologies have profoundly transformed cattle breeding by accelerating genetic progress and enabling the dissemination of elite genetics. In this article, I present a perspective based on more than 40 years of practical experience in embryo technologies within Auriva-Elevage, a cooperative organization serving 30,000 farmers in southern France. The development of embryo transfer in France was closely linked to genetic and sanitary challenges, particularly the introduction of North American Holstein genetics and the restrictions on live animal imports due to infectious diseases such as Infectious Bovine Rhinotracheitis. These constraints stimulated the development of national expertise in embryo transfer. Over the years, our team has implemented and adapted a wide range of reproductive technologies including in vivo embryo production and embryo transfer, cryopreservation, embryo sexing, ovum pick-up (OPU), in vitro embryo production (IVP), embryo biopsy, genomic evaluation of embryos, and laser-assisted biopsy techniques. The genomic revolution dramatically increased the strategic value of OPU-IVP for the rapid multiplication of elite donor females. In addition to technological developments, the success of these programs has depended heavily on internal training, collaboration with national organizations such as ELIANCE (previously UNCEIA, ALLICE) and research institutes including INRAE and Toulouse veterinary school, as well as strong international exchanges through scientific networks. Practical examples such as the use of embryo biopsy to prevent genetic diseases demonstrate the applied value of these technologies in breeding programs. This review highlights the technical evolution, organizational structures, and human expertise that have shaped the implementation of reproductive biotechnologies in cattle breeding and discusses the importance of anticipating future needs to ensure continued genetic progress.
A commercial sire line (C) and an experimental population selected solely for increased 16-wk BW (F) were reciprocally crossed to produce crossbred F1 and F2 progeny. The F1 and F2 crosses were used to evaluate the presence of nonadditive genetic variance for growth and reproductive traits. The crosses demonstrated improved growth performance as indicated by heterosis for 16- and 20-wk BW. The difference in BW was, however, reversed at maturity as indicated by negative heterosis for BW at maturity. The F1 and F2 crosses also exhibited heterosis for walking ability. Heterosis for reproductive traits was greater than for growth. The F1 crosses produced approximately 20 eggs more in a 180-day production season than the parental populations. This difference was halved in F2 generation hens. Improved egg production was achieved both through an increase in the rate of egg production and through a reduction in broodiness. The present experiment indicates that there is potential for significant heterosis for growth and reproduction in some crosses in the domestic turkey. The results also indicate that heterosis can be considerable, even in crosses of lines which do not differ greatly in BW or reproductive performance.
The free-living nematode Caenorhabditis elegans has been used extensively for studies in developmental and reproductive genetics. Recently, toxicologic studies have been initiated using specific sex chromosome mutations. In the present study, high incidence of male (him) mutants, him-5 and him-8, were treated with dimethyl sulfone (DMSO2), the primary metabolite of dimethyl sulfoxide (DMSO). In addition to differential effects on X-chromosome nondisjunction, loss of viability and fertility were observed. Much lower concentrations of DMSO2 were required to elicit the same aberrational effects characteristic of DMSO (1); thus, the toxicity of the former was significantly more potent. The observed decrease in life span was associated with senescent morphology of meiotic prophase nuclei, such that nuclei from young and old specimens could not be differentiated. Aging in oocytes at pachytene is characterized by nucleo-cytoplasmic aberrations, increased density of the nucleoplasm and cytoplasm, and decrease in numbers of mitochondria. Increasing concentrations of DMSO2 resulted in a corresponding decrease in fertility and increased production of abnormal gametes. At DMSO2 concentrations higher than 1.0%, synaptonemal complexes (SC) were absent from pachytene nuclei; thus, effective pairing and segregation of homologous chromosomes was prohibited. Since the SC is essential for regulating pairing and subsequent separation of bivalents, the lack of an SC explains the loss of fertility, due to the production of unbalanced gametes, observed in DMSO2-treated specimens.
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The genetic landscape of human infertility is complex with diverse etiologies. Identifying the underlying etiology is crucial for guiding reproductive decisions and improving management for infertile couples. Here, we aim to report on the molecular spectrum of monogenic genetic causes of reproductive failure. Over a 3-year period, we recruited all infertile couples considering assisted reproductive technologies (ART) for whom the underlying genetic cause had been identified, in either partner, using exome sequencing (ES). Clinical data of all participants along with their hormonal profiles, sonographic findings and spermograms were recorded. The study included 50 couples with primary infertility. Clinically, male factor infertility was documented in 26 patients, female factor infertility in 10, while reproductive failure was unexplained in the remaining 14 couples. All participating couples had potentially disease-causing variants in infertility genes. ES identified variants related to male infertility in 26 men, while variants in female infertility-related genes were detected in the remaining couples (n = 24). According to ACMG classification criteria, 78% (39/50) of couples harbored pathogenic/likely pathogenic (P/LP) variants, whereas 22% (11/50) carried variants of uncertain significance (VUS). In view of the identified genetic etiologies, the cohort was stratified into two groups based on the predicted reproductive outcome: (1) couples with significantly impaired reproductive potential, and (2) couples who can have biological children using appropriate medical interventions. However, classifications involving VUS were interpreted cautiously and considered exploratory. This study provides further evidence for the molecular heterogeneity of human infertility and highlights the usefulness of genetic testing for infertile couples pursuing ARTs.