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PubMed1991

Characteristics of a genetic polymorphism for reproductive photoresponsiveness in the white-footed mouse (Peromyscus leucopus).

Wild populations of Peromyscus are often composed of individuals that vary greatly in their reproductive response to photoperiod. A population of white-footed mice (P. leucopus) from Michigan (43 degrees N) was subjected to mass selection in the laboratory both for and against reproductive photoresponsiveness for four generations. The first generation of selection yielded one line of mice in which about 80% of the individuals were classified as reproductively photoresponsive (i.e., with undeveloped reproductive tracts when reared in short days, 8L: 16D) and another in which only about 20% were reproductively photoresponsive. Some and perhaps most of this difference was accounted for by changes in degree of responsiveness to photoperiod rather than by alterations in the proportion of discrete responsive vs. unresponsive phenotypes. Alteration of critical day length was not a factor. Three more generations of selection failed to change the proportions noted above significantly. Although the genetic control of reproductive photoresponsiveness is undoubtedly complex, a single variable locus may be responsible for much of the heritable variation present in this population. These results also suggest that natural populations contain genetically determined phenotypes that are intermediate between absolutely photoresponsive and absolutely unresponsive. The factors that might promote maintenance of heterogeneity of reproductive photoresponsiveness in a wild population of rodents are considered.

Animals↗
PubMed1990

Factors influencing the reproductive decision after genetic counseling.

Here we report a follow-up study involving interviews with 164 couples 2-3 years after genetic counseling to assess the influence of various factors on their reproductive planning. The results show that the desire to have children and the absence of personal experience with the disorder (no close relative being affected) are important single factors for the decision to opt for having children after genetic counseling. The magnitude of the genetic risk is of relative importance in reproductive planning. Seventy percent of the couples with a high genetic risk (greater than 15%) opted for having children. When the disorder was perceived as severe and the risk was interpreted as high, 72% opted for having children. The availability of prenatal diagnosis became important only in combination with a high genetic risk (greater than 15%). Forty-seven percent of the couples with a high genetic risk refrained from having children when prenatal diagnosis was not available. In the absence of prenatal diagnosis, couples who had an affected child were more cautious about trying again than those who did not--50% versus 14% decided to abstain. This study has provided some insight into the complexity of reproductive decision-making after genetic counseling. The findings may help genetic counselors and clinical geneticists understand and support counselees in their decision-making process, which is "multi-factorial."

Chromosome Aberrations↗
PubMed1987

Simulation of genetic control of reproduction in beef cows. III. Within-herd breeding value estimation with known breeding dates.

Procedures for breeding value estimation for reproductive traits with known breeding dates were developed and tested using results of a computer simulation model of genetic control of bovine reproduction. The model generated realized reproductive outputs as a function of underlying genetic variation in two independent traits: conception rate (CR), which was indicative of the ability to conceive given estrus, and PPI, the postpartum interval from calving to first estrus. Two scenarios were considered. In the first, all cows were assumed to be cycling at the start of breeding and to be bred artificially. For this scenario, breeding values for CR could be estimated from information on observed breeding and calving dates by using a categorical trait, multi-stage selection model. Breeding value estimation for PPI, however, required actual measurement of PPI because if PPI and CR are genetically independent and if all cows are cycling at the beginning of breeding, subsequent breeding and calving dates are independent of PPI. The second scenario recognized that not all females would be cycling at the start of breeding. For this scenario, the categorical trait, multi-stage selection model could still be applied for breeding value estimation for CR, but accumulation of data across years was complicated by a need to consider the lifetime reproductive pattern of the individual rather than just the sum of each year's performances. Breeding value estimates for PPI could be obtained from observed breeding and calving dates for this scenario, but required consideration of the distributional properties of PPI.

Animals↗
PubMed1996

Genetic screening for reproductive planning: methodological and conceptual issues in policy analysis.

OBJECTIVES: This paper explores several critical assumptions and methodological issues arising in cost-effectiveness analyses of genetic screening strategies in the reproductive setting. METHODS: Seven issues that arose in the development of a decision analysis of alternative strategies for cystic fibrosis carrier screening are discussed. Each of these issues required a choice in technique. RESULTS: The presentations of these analyses frequently mask underlying assumptions and methodological choices. Often there is no best choice. In the case of genetic screening in the reproductive setting, these underlying issues often touch on deeply felt human values. CONCLUSIONS: Space limitations for published papers often preclude explaining such choices in detail; yet these decisions determine the way the results should be interpreted. Those who develop these analyses need to make sure that the implications of important assumptions are understood by the clinicians who will use them. At the same time, clinicians need to enhance their understanding of what these models truly mean and how they address underlying clinical, ethical, and economic issues.

Cystic Fibrosis↗
PubMed1983

[Genetic endocrine and ethological mechanisms of differential reproduction. I. A comparative genetic analysis of the basal testosterone level in the blood plasma and the relative weight of the testicles and accessory sex glands in male laboratory mice].

Comparative genetic study of the basal plasma testosterone level, relative weights of testicles, seminal vesicles, and preputial glands in 13 strains of laboratory mice showed significant interstrain differences in all indices studied. Under the relative rest condition, a significant positive interstrain (genotypic) correlation was found between basal blood testosterone level and the weight of preputial glands and testicles. At the same time, no intrastrain (paratypic) correlations between hormonal and morphometric indices under study were found. An important positive and highly significant paratypic correlative dependence was seen between the relative weights of seminal vesicles and preputial glands.

Animals↗
PubMed2000

The critical and expanding role of genetics in assisted reproduction.

With the progress of the human gene mapping initiative, it is expected that the entire genome will be mapped within two years. A significant use for these data will centre on testing for genetic disease. Professionals associated with assisted reproduction are presented with a very special subset of the population, namely, couples suffering from infertility. Infertility may occur in the male, the female or both partners and may be heritable. Infertility, subfertility or recurrent spontaneous miscarriage is associated with chromosomal or genetic anomalies, suggesting that basic developmental genetics should be a part of the education of the physician or clinical embryologist. A review of the most common infertility-associated chromosomal and genetic diseases for which genetic testing has become routine in infertile parents and in the products of assisted reproduction through preimplantation genetic diagnosis (PGD) and prenatal testing follows. Less common genetic diseases that have compromising effects on reproduction and which are likely to be encountered by providers of assisted reproduction are also considered.

Adult↗
PubMed2003

Toward the genetics of mammalian reproduction: induction and mapping of gametogenesis mutants in mice.

The genetic control of mammalian gametogenesis is inadequately characterized because of a lack of mutations causing infertility. To further the discovery of genes required for mammalian gametogenesis, phenotype-driven screens were performed in mice using random chemical mutagenesis of whole animals and embryonic stem cells. Eleven initial mutations are reported here that affect proliferation of germ cells, meiosis, spermiogenesis, and spermiation. Nine of the mutations have been mapped genetically. These preliminary studies provide baselines for estimating the number of genes required for gametogenesis and offer guidance in conducting new genetic screens that will accelerate and optimize mutant discovery. This report demonstrates the efficacy and expediency of mutagenesis to identify new genes required for mammalian gamete development.

Animals↗
PubMed2003

Constraints on the evolution of males and sexual dimorphism: field estimates of genetic architecture of reproductive traits in three populations of gynodioecious Fragaria virginiana.

To understand how genetic constraints may limit the evolution of males and sexual dimorphism in a gynodioecious species, I conducted a quantitative genetic experiment in a gynodioecious wild strawberry, Fragaria virginiana. I estimated and compared genetic parameters (narrow-sense heritabilities, between-trait and between-sex genetic correlations, as well as phenotypic and genetic variance-covariance matrices) in the two sex morphs from three populations grown in a common field garden. I measured pollen and ovule production per flower, petal size, fruit set, and flower number. My major findings are as follows. (1) The presence of a phenotypic trade-off between pollen production and fruit set in hermaphrodites reflects a negative genetic correlation in the narrow sense that is statistically significant when pooled across populations. (2) The main constraints on the evolution of males are low genetic variation for pollen per flower and strong positive correlations associated with ovule number (e.g., between pollen and ovules in hermaphrodites, and between ovules in hermaphrodites and females). (3) Traits with the lowest levels of sexual dimorphism (ovule number and flower number) have the highest between-sex genetic correlations suggesting that overlap in the expression of genes in the sex morphs constrains their independent evolution. (4) There are significant differences in G matrices between sex morphs but not among populations. However, evidence that male-female trait correlations in hermaphrodites were lower in populations with higher frequencies of females may indicate subtle changes in genetic architecture.

Biological Evolution↗
PubMed1983

Reciprocal recurrent selection for 21-day litter weight of crossbred gilts. I. Selection applied and genetic change in reproduction of crossbred gilts.

Six cycles of reciprocal recurrent selection (RRS) between Line 8 (Duroc) and Line 9 (Beltsville No. 1) were completed at the Fort Reno Livestock Research Center, El Reno, Oklahoma. A randomly mated control line was maintained. Each cycle of selection required three seasons. Selection of purebred pigs (born in the second season) was based on the mean 21-d litter weight of their maternal and paternal half-sib crossbred gilts that were born in the first season and farrowed in the third season (XB21DLWT). On the average, 5.8 maternal and paternal half-sib gilts contributed to the mean XB21DLWT for each purebred individual. The average potential selection differential for XB21DLWT was 5.64 kg, but only 70.2% of this value was realized in the initial selection (3.95 kg). Disease problems and unsoundness were the primary reasons for this discrepancy. The potential, initial, final and weighted final standardized selection differentials for females averaged 61, 60, 55 and 47%, respectively, of the corresponding differentials for males. Standardized selection differentials were similar for Line 8 and Line 9. The estimate of realized heritability for XB21DLWT was .076 +/- .319 for the average of 8 X 9 and 9 X 8 gilts. Environmental trends, estimated from control data, were not significant for any of the traits evaluated. The genetic change in reproductive ability of 8 X 9, 9 X 8 and their unweighted average was estimated by regressing the deviation of the line mean from the control mean on generation number. In general, estimates of genetic change for litter size, litter weight and average pig weight/litter at 0, 21 and 42 d of age were not significant, but all estimates were favorable. The estimated genetic change for 21-d litter weight was 1.04 +/- 1.25 kg/cycle of selection. Based on these results and considering the complexity of RRS, the increase in generation interval and the expected decline in purebred performance that theoretically should accompany successful RRS, it seems doubtful that RRS can be more beneficial than selection based on purebred performance as a method to improve productivity of crossbred gilts.

Animals↗
PubMed1992

Structure of breeding programs to capitalize on reproductive technology for genetic improvement.

Potential rates of genetic progress are limited by biological constraints, which along with genetic parameters determine the structure of breeding programs to be employed for maximum genetic improvement. The objective here is to determine whether current progeny-testing programs in dairy cattle, which have been dictated and constrained by low female reproductive rates, need to be changed to capitalize on new reproductive technologies and how these changes should be implemented. Many differences between breeding programs diminish when selection on animal model genetic evaluations across all age and population groups is adopted as a strategy. Progeny-testing schemes then evolve toward dispersed open nucleus breeding schemes when multiple ovulation and embryo transfer is used on bull-dams. Nucleus breeding schemes have been advocated to capitalize on embryo transfer technology. In nucleus breeding schemes utilizing high reproductive rates, inbreeding, rather than reproductive rate, poses a limit to genetic progress, and strategies that maximize response to selection while limiting inbreeding need to be employed. One strategy is mating each dam to several sires rather than only one sire. In vitro embryo production techniques can be used to facilitate such mating strategies. Large-scale in vitro embryo production programs, in which large numbers of embryos per female are tested in the commercial population, offer the greatest potential for genetic gain with low rates of inbreeding. Cloning has an impact mainly on methods for dissemination of genetic improvement. Breeding herds, genetically inferior to marketed clones, are needed for continuous genetic gain. Reproductive technologies offer the potential for genetic improvement. Whether new breeding programs require changes in population structure, e.g., by creation of nucleus breeding herds, depends mainly on logistics and on quantity and quality of field information.

Animals↗
PubMed1976

Genetics and asexual reproduction of the sea anemone Metridium senile.

1. Metridium senile was studied for phosphohexose-isomerase variation at three locations on Cape Cod, Massachusetts: Woods Hole, Cape Cod Canal, and Barnstable Town Boat Harbor. 2. All three locations exhibited significant polymorphism for PHI. 3. Mapping of individual polyps was performed at Barnstable to analyze spatial distributions of clones and genotypes. 4. In Barnstable, PHI does not depart significantly from Hardy-Weinberg expectations at the time of establishment of new polyps, and establishment of larvae is spatially random with respect to PHI genotype. 5. Asexual reproduction was uses as a meausre of the relative success of different PHI genotypes. There are indications that not all genotypes are equally likely to produce large clones. 6. There is significant heterogeneity among the three locations with respect to PHI genotype frequencies, suggesting that there may be geographical differentiation of the populations. 7. Sessile, asexual organisms provide powerful tools for examining the dynamic aspects of genetic structure in natural populations.

Animals↗
PubMed1992

The check-up of reproductive health and genetic counseling.

The Hungarian Family Planning Program was a feasibility study on combining methods of periconceptional care. The first step was the check-up of reproductive health, including family history of the couples, case history of females, pre-pregnancy examination (vaginal and cervical smears), and the measurement of basal body temperature, sperm examination, psycho-sexual exploration and exclusion of some risk factors. This preconception screening program was carried out by graduate trainee nurses to identify those participants secondary health services. The data of 4,240 couples attending in the Budapest Center indicated a useful relationship between the check-up of reproductive health and genetic counseling clinics, by selecting couples requiring genetic counseling and preventing other couples making unnecessary visits.

Adolescent↗
PubMed1988

Simulation of genetic control of reproduction in beef cows. IV. Within-herd breeding value estimation with pasture mating.

Procedures for breeding value estimation for reproductive traits under pasture mating conditions were developed and tested using a computer simulation model of genetic control of bovine reproduction. The model generated annual calving rates (BCR) (0 or 1) and calving dates (CD) for each cow as a function of underlying genetic variation in two independent traits: single-service conception rate, which was indicative of the ability to conceive when estrus occurs, and postpartum interval (PPI) from calving to first estrus. Observed values for BCR and CD were shown to be complex, nonlinear functions of breeding values for ability to conceive (CRG) and for postpartum interval (PPIG) and of the previous CD. Effects of CRG on BCR and CD were small at high values of CRG, but these effects increased as CRG declined. Effects of PPIG on BCR and CD were small for cows that previously calved within the first 21 d of the calving season, but these effects increased for cows that calved after d 21. Previous CD had substantial nongenetic carryover effects on both BCR and CD. Unbiased estimates of CRG and PPIG could not be derived in the absence of breeding information. However, CD were reasonably highly correlated with breeding values for ability to conceive, provided information on open cows was included in the evaluation. Calving dates were only weakly associated with breeding values for PPI, in part because of the relatively short mean PPI (70 d) that was simulated.

Animals↗
PubMed2001

Genetic parameters of reproductive traits in Brown Tsaiya ducks artificially inseminated with semen from Muscovy drakes.

A selection experiment on maximum duration of fertility of Brown Tsaiya ducks after artificial insemination (AI) with pooled Muscovy semen has been conducted since 1992. The Brown Tsaiya ducks were divided into two lines: a control line (T) with no selection and a selected line (S). The traits measured were the number of eggs set that were laid from Days 2 to 15 after one AI (NES), the number of fertile eggs at candling (NEF), the total number of dead embryos (NED), the maximum duration of fertility (MD), and the number of hatched mule ducklings (NEH). The selected trait was NEF. Six generations with a total of 2,127 females were measured. The variance components were estimated for each line in a multiple-trait animal model, using the restricted maximum likelihood (REML) methodology, which yields estimates free of bias caused by selection and inbreeding. Estimates of the heritability and genetic correlation from the two lines were very similar. Heritabilities in the S and T lines, respectively, were 0.14 and 0.10 for NES, 0.30 and 0.26 for NEF, 0.06 and 0.09 for NED, 0.28 and 0.21 for MD, and 0.18 and 0.19 for NEH. High and favorable genetic correlations existed between NEF and MD (0.96 and 0.92), between NEF and NEH (0.86 and 0.91), and between MD and NEH (0.90 and 0.82). The results suggested that selection for NEF could improve the maximum duration of fertility, but it could be useful to check the estimates of genetic parameters in a meat-type female duck.

Animals↗
PubMed2003

Genetic structure and reproduction dynamics of Salix reinii during primary succession on Mount Fuji, as revealed by nuclear and chloroplast microsatellite analysis.

The early stage of volcanic desert succession is underway on the southeastern slope of Mount Fuji. We used markers of nuclear microsatellites (simple sequence repeats; SSR) and chloroplast microsatellites (cpSSR) to investigate the population genetic structure and reproduction dynamics of Salix reinii, one of the dominant pioneer shrubs in this area. The number of S. reinii genets in a patch and the area of the largest genet within the patch increased with patch area, suggesting that both clonal growth and seedling recruitment are involved in the reproduction dynamics of S. reinii. Five polymorphic cpSSR markers were developed for S. reinii by sequencing the noncoding regions between universal sequences in the chloroplast genome. Nineteen different cpSSR haplotypes were identified, indicating that S. reinii pioneer genets were created by the long-distance dispersal of seeds originating from different mother genets around the study site, where all vegetation was destroyed during the last eruption. Furthermore, the clustered distributions of different haplotypes within each patch or plot suggested that newly colonized genets tended to be generated from seeds dispersed near the initially established mother genets. These results revealed that the establishment of the S. reinii population on the southeastern slope of Mount Fuji involved two sequential modes of seed dispersal: long-distance dispersal followed by short-distance dispersal.

Cell Nucleus↗
PubMed1996

Race, genetics, and human reproductive strategies.

The international literature on racial differences is reviewed, novel data are reported, and a distinct pattern is found. People of east Asian ancestry and people of African ancestry average at opposite ends of a continuum, with people of European ancestry averaging intermediately, albeit with much variability within each major race. The racial matrix emerges from measures taken of reproductive behavior, sex hormones, twinning rate, speed of physical maturation, personality, family stability, brain size, intelligence, law abidingness, and social organization. An evolutionary theory of human reproduction is proposed, familiar to biologists as the r-K scale of reproductive strategies. At one end of this scale are r-strategies, which emphasize high reproductive rates; at the other end are K-strategies, which emphasize high levels of parental investment. This scale is generally used to compare the life histories of widely disparate species, but here it is used to describe the immensely smaller variations among human races. It is hypothesized that, again on average, Mongoloid people are more K-selected than Caucasoids, who are more K-selected than Negroids. The r-K scale of reproductive strategies is also mapped on to human evolution. Genetic distances indicate that Africans emerged from the ancestral hominid line about 200,000 years ago, with an African/non-African split about 110,000 years ago, and a Caucasoid/Mongoloid split about 41,000 years ago. Such an ordering fits with and explains how and why the variables cluster.

Biological Evolution↗