Sex Ratio: The number of males per 100 females.Sex Factors: Maleness or femaleness as a constituent element or influence contributing to the production of a result. It may be applicable to the cause or effect of a circumstance. It is used with human or animal concepts but should be differentiated from SEX CHARACTERISTICS, anatomical or physiological manifestations of sex, and from SEX DISTRIBUTION, the number of males and females in given circumstances.Sex Determination Processes: The mechanisms by which the SEX of an individual's GONADS are fixed.Sex Characteristics: Those characteristics that distinguish one SEX from the other. The primary sex characteristics are the OVARIES and TESTES and their related hormones. Secondary sex characteristics are those which are masculine or feminine but not directly related to reproduction.Sex Determination Analysis: Validation of the SEX of an individual by inspection of the GONADS and/or by genetic tests.Sex Preselection: Methods for controlling genetic SEX of offspring.Reproduction: The total process by which organisms produce offspring. (Stedman, 25th ed)Wasps: Any of numerous winged hymenopterous insects of social as well as solitary habits and having formidable stings.Sex Chromosomes: The homologous chromosomes that are dissimilar in the heterogametic sex. There are the X CHROMOSOME, the Y CHROMOSOME, and the W, Z chromosomes (in animals in which the female is the heterogametic sex (the silkworm moth Bombyx mori, for example)). In such cases the W chromosome is the female-determining and the male is ZZ. (From King & Stansfield, A Dictionary of Genetics, 4th ed)Hymenoptera: An extensive order of highly specialized insects including bees, wasps, and ants.Sex: The totality of characteristics of reproductive structure, functions, PHENOTYPE, and GENOTYPE, differentiating the MALE from the FEMALE organism.Birth Rate: The number of births in a given population per year or other unit of time.Sexual Behavior, Animal: Sexual activities of animals.Competitive Behavior: The direct struggle between individuals for environmental necessities or for a common goal.Sex Differentiation: The process in developing sex- or gender-specific tissue, organ, or function after SEX DETERMINATION PROCESSES have set the sex of the GONADS. Major areas of sex differentiation occur in the reproductive tract (GENITALIA) and the brain.Paternal Exposure: Exposure of the male parent, human or animal, to potentially harmful chemical, physical, or biological agents in the environment or to environmental factors that may include ionizing radiation, pathogenic organisms, or toxic chemicals that may affect offspring.Wolbachia: A genus of bacteria comprised of a heterogenous group of gram-negative small rods and coccoid forms associated with arthropods. (From Bergey's Manual of Systematic Bacteriology, vol 1, 1984)Fertility: The capacity to conceive or to induce conception. It may refer to either the male or female.Litter Size: The number of offspring produced at one birth by a viviparous animal.Sex Distribution: The number of males and females in a given population. The distribution may refer to how many men or women or what proportion of either in the group. The population is usually patients with a specific disease but the concept is not restricted to humans and is not restricted to medicine.Unsafe Sex: Sexual behaviors which are high-risk for contracting SEXUALLY TRANSMITTED DISEASES or for producing PREGNANCY.Disorders of Sex Development: In gonochoristic organisms, congenital conditions in which development of chromosomal, gonadal, or anatomical sex is atypical. Effects from exposure to abnormal levels of GONADAL HORMONES in the maternal environment, or disruption of the function of those hormones by ENDOCRINE DISRUPTORS are included.Biological Evolution: The process of cumulative change over successive generations through which organisms acquire their distinguishing morphological and physiological characteristics.Nesting Behavior: Animal behavior associated with the nest; includes construction, effects of size and material; behavior of the adult during the nesting period and the effect of the nest on the behavior of the young.Population Dynamics: The pattern of any process, or the interrelationship of phenomena, which affects growth or change within a population.Y Chromosome: The male sex chromosome, being the differential sex chromosome carried by half the male gametes and none of the female gametes in humans and in some other male-heterogametic species in which the homologue of the X chromosome has been retained.Pregnancy: The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH.Birth Order: The sequence in which children are born into the family.Sex Workers: People who engage in occupational sexual behavior in exchange for economic rewards or other extrinsic considerations.Oviposition: The process of laying or shedding fully developed eggs (OVA) from the female body. The term is usually used for certain INSECTS or FISHES with an organ called ovipositor where eggs are stored or deposited before expulsion from the body.AzerbaijanVomeronasal Organ: An accessory chemoreceptor organ that is separated from the main OLFACTORY MUCOSA. It is situated at the base of nasal septum close to the VOMER and NASAL BONES. It forwards chemical signals (such as PHEROMONES) to the CENTRAL NERVOUS SYSTEM, thus influencing reproductive and social behavior. In humans, most of its structures except the vomeronasal duct undergo regression after birth.Infanticide: The killing of infants at birth or soon after.Malawi: A republic in southern Africa east of ZAMBIA and MOZAMBIQUE. Its capital is Lilongwe. It was formerly called Nyasaland.Parturition: The process of giving birth to one or more offspring.Electronic Mail: Messages between computer users via COMPUTER COMMUNICATION NETWORKS. This feature duplicates most of the features of paper mail, such as forwarding, multiple copies, and attachments of images and other file types, but with a speed advantage. The term also refers to an individual message sent in this way.Food Dispensers, Automatic: Mechanical food dispensing machines.Editorial Policies: The guidelines and policy statements set forth by the editor(s) or editorial board of a publication.Authorship: The profession of writing. Also the identity of the writer as the creator of a literary production.Periodicals as Topic: A publication issued at stated, more or less regular, intervals.Postal Service: The functions and activities carried out by the U.S. Postal Service, foreign postal services, and private postal services such as Federal Express.Internet: A loose confederation of computer communication networks around the world. The networks that make up the Internet are connected through several backbone networks. The Internet grew out of the US Government ARPAnet project and was designed to facilitate information exchange.Neurotic Disorders: Disorders in which the symptoms are distressing to the individual and recognized by him or her as being unacceptable. Social relationships may be greatly affected but usually remain within acceptable limits. The disturbance is relatively enduring or recurrent without treatment.Investments: Use for articles on the investing of funds for income or profit.Marketing: Activity involved in transfer of goods from producer to consumer or in the exchange of services.TaiwanModels, Economic: Statistical models of the production, distribution, and consumption of goods and services, as well as of financial considerations. For the application of statistics to the testing and quantifying of economic theories MODELS, ECONOMETRIC is available.Financial Management: The obtaining and management of funds for institutional needs and responsibility for fiscal affairs.Genetics: The branch of science concerned with the means and consequences of transmission and generation of the components of biological inheritance. (Stedman, 26th ed)Drosophila: A genus of small, two-winged flies containing approximately 900 described species. These organisms are the most extensively studied of all genera from the standpoint of genetics and cytology.Drosophila Proteins: Proteins that originate from insect species belonging to the genus DROSOPHILA. The proteins from the most intensely studied species of Drosophila, DROSOPHILA MELANOGASTER, are the subject of much interest in the area of MORPHOGENESIS and development.Drosophila melanogaster: A species of fruit fly much used in genetics because of the large size of its chromosomes.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Genetics, Population: The discipline studying genetic composition of populations and effects of factors such as GENETIC SELECTION, population size, MUTATION, migration, and GENETIC DRIFT on the frequencies of various GENOTYPES and PHENOTYPES using a variety of GENETIC TECHNIQUES.

Evaluation of life-cycle herd efficiency in cow-calf systems of beef production. (1/1154)

A deterministic beef efficiency model (BEM) was used to evaluate life-cycle herd efficiency (LCHE) in cow-calf beef production systems using four breed groups of beef cattle. The breed groups were Beef Synthetic #1 (SY1), Beef Synthetic #2 (SY2), Dairy Synthetic (DS), and purebred Hereford (HE). The LCHE was defined over the lifetime of the herd as the ratio of total output (lean meat equivalent) to total input (feed equivalent). Breed differences in LCHE were predicted with the larger/slower maturing DS being most efficient at each age of herd disposal and reproductive rate. This was mainly because, at any average age at culling, the dams of DS breed group were less mature and so had been carrying relatively lower maintenance loads for shorter periods and positively influencing LCHE. Higher LCHE was predicted with improvement in reproductive performance if there were no associated extra costs. However, this declined markedly if there was a delay in marketing of offspring. As average age at culling increased from 4 to 6 yr, efficiency declined sharply, but it began to recover beyond this age in most breed groups. We concluded that the slower maturing DS breed group may be more efficient on a herd basis in cow-calf systems and that improvements in reproductive rate not associated with extra costs improve life-cycle efficiency. Culling cows soon after their replacements are produced seems efficient.  (+info)

Placenta previa: preponderance of male sex at birth. (2/1154)

To determine the relation between placenta previa and male sex at birth, the authors conducted two types of analysis: 1) a historical cohort analysis of singleton live births in New Jersey hospitals during 1989-1992 (N = 447,963); and 2) a meta-analysis of previously published studies on the subject. For the cohort analysis, subject mother-infant dyads were identified from linked birth certificate and maternal and infant hospital claims data. The infant's sex for mothers with an International Classification of Diseases, Ninth Revision, Clinical Modification, code of 641.0-641.1 for placenta previa (n = 2,685) was compared with infant's sex for mothers without placenta previa (n = 445,270). For the meta-analysis, seven published articles were located and summary effects were calculated using both fixed-effect and random-effects models. In the present cohort study, the male:female ratio at birth was significantly higher in women with placenta previa (1.19) than in those without placenta previa (1.05) (p<0.001). The association of placenta previa with male sex persisted when the analysis was either stratified or adjusted for the effects of maternal age, maternal parity, maternal smoking during the index pregnancy, race/ethnicity, the infant's gestational age, and the infant's birth weight. The meta-analytic results from the fixed-effect and random-effects models showed a 14% excess of placenta previa when women were carrying a viable male fetus as compared with a viable female fetus during pregnancy. The results were the same regardless of whether the present cohort study was included in the meta-analysis. In conclusion, the evidence obtained from these analyses strongly argues for an association between placenta previa and male sex at birth. The mechanism for this association remains to be determined.  (+info)

Spiroplasma poulsonii sp. nov., a new species associated with male-lethality in Drosophila willistoni, a neotropical species of fruit fly. (3/1154)

Progenies from some wild-caught females of Drosophila willistoni and three other sibling species are entirely female. The proclivity for production of unisexual female progeny by these flies was named the sex ratio (SR) trait and was originally thought to be genetic. However, experiments in the laboratory of Donald F. Poulson in the early 1960s demonstrated that this 'trait' was vertically transmitted and infectious, in that it could be artificially transferred by injection from infected females to non-infected females. Motile, helical micro-organisms were observed in females showing the trait. In 1979, the SR organisms were designated as group II in the informal spiroplasma classification system. The organisms proved to be extremely fastidious, but were eventually cultivated in a very complex cell-free medium (H-2) after initial co-cultivation with insect cells. Cultivation in the H-2 medium and the subsequent availability of a triply cloned strain (DW-1T) permitted comparative studies. Cells of strain DW-1T were helical, motile filaments 200-250 nm in diameter and were bound by a single trilaminar membrane. Cells plated on 1.8% Noble agar formed small satellite-free colonies 60-70 microns in diameter with dense centres and uneven edges. The temperature range for growth was 26-30 degrees C; optimum growth occurred at 30 degrees C, with a doubling time in H-2 medium of 15.8 h. The strain passed through filters with 220 nm, but not 100 nm, pores. Reciprocal serological comparisons of strain DW-1T with representatives of other spiroplasma groups showed an extensive pattern of one-way crossing when strain DW-1T was used as antigen. However, variable, usually low-level reciprocal cross-reactions were observed between strain DW-1T and representatives of group I sub-groups. The genome size of strain DW-1T was 2040 kbp, as determined by PFGE. The G + C content was 26 +/- 1 mol%, as determined by buoyant density and melting point methods. The serological and molecular data indicate that strain DW-1T is separated from group I representative strains sufficiently to justify retention of its group status. Continued group designation is also indicated by the ability of SR spiroplasmas to induce male lethality in Drosophila, their vertical transmissibility and their extremely fastidious growth requirements. Group II spiroplasmas, represented by strain DW-1T (ATCC 43153T), are designated Spiroplasma poulsonii.  (+info)

Estimating population size by genotyping faeces. (4/1154)

Population size is a fundamental biological parameter that is difficult to estimate. By genotyping coyote (Canis latrans) faeces systematically collected in the Santa Monica Mountains near Los Angeles, California, we exemplify a general, non-invasive method to census large mammals. Four steps are involved in the estimation. First, presumed coyote faeces are collected along paths or roadways where coyotes, like most carnivores, often defaecate and mark territorial boundaries. Second, DNA is extracted from the faeces and species identity and sex is determined by mitochondrial DNA and Y-chromosome typing. Third, hypervariable microsatellite loci are typed from the faeces. Lastly, rarefaction analysis is used to estimate population size from faecal genotypes. This method readily provides a point count estimate of population size and sex ratio. Additionally, we show that home range use paternity and kinship can be inferred from the distribution and relatedness patterns of faecal genotypes.  (+info)

Factors affecting the number of teats in pigs. (5/1154)

The factors that affect the number of teats in pigs are of interest for both biological and practical reasons. Previous work indicates that there is a genetic component, principally from the dam. The proportion of males in a litter appears to be related to the anogenital distance of the gilts in the litter, possibly as a result of the intrauterine position effect. The present study investigated whether litter size, litter sex ratio, anogenital distance, crown-rump length, distance from base of skull to base of tail, and the number of teats on the dam and boar affected the number of teats on gilts. Stepwise multiple regression on litter mean values (adjusted r2 = 0.178) indicated that two factors were significant: the number of teats on the dam (standard coefficient 0.311) and the proportion of males in the litter (standard coefficient -0.282). A greater number of teats on the dam and a lower proportion of males in the litter resulted in a greater number of teats on the gilt. When the analysis was run using individual gilts as the independent units (adjusted r2 = 0.073), the number of teats on the dam (standard coefficient 0.207), the proportion of males in the litter (standard coefficient -0.135), and the weaning weight of the gilt (standard coefficient 0.083) were all significant predictors of the number of teats. This evidence suggests that teat number in female pigs is related to the proportion of males in the litter.  (+info)

Allosomal and autosomal control of sex ratio in PHH and PHL mice. (6/1154)

When male mice from inbred PHH (sex ratio .535) and PHL (.435) are mated to females of various inbred lines, the sex ratio follows the male parent. The sex ratios from litters sired by reciprocal cross F1 males (letting A represent a set of autosomes) are 0.510 from AH/AL, XL/YH and 0.469 from AH/AL, XH/YL. The difference is statistically significant but only half the difference between pure strains. The paternal effect, presumably due to the Y, persists in progeny of the two kinds of F2 males. In backcrosses to the female parent, resulting finally in AH/AH, XH/YL and AL/AL, XL/YH, and in outcrosses, the effect of the Y chromosome does not persist, indicating that neither the Y alone, nor the autosomes alone, will cause the sex ratio to depart significantly from equality of sexes. When pairs of males in all possible combinations were presented with C57BL/6 females mating success gave the following ranking: AH-YL, AL-YL, AH-YH, AL-YH. The combination of autosomes from PHH and Y-chromosome from PHL seems to confer the greatest competitive advantage.  (+info)

Muscle growth and development in normal-sex-ratio and all-female diploid and triploid Atlantic salmon. (7/1154)

Muscle development and growth were investigated in diploid populations of normal-sex-ratio and all-female Atlantic salmon (Salmo salar L.) and their triploid counterparts produced by high-pressure treatment. Somites were formed at the rate of 6 h-1 in both diploids and triploids at 6 degrees C. The rostral-to-caudal development of myotubes, myofibrils and acetylcholinesterase staining at the myosepta was slightly more advanced in triploid than in diploid fish, although the differences were smaller than among individual families. The c-met receptor tyrosine kinase was used as a molecular marker for the satellite cells involved in postembryonic muscle growth. Satellite cell nuclei comprised 17.5 % of total myonuclei in smolts and they were 24 % more abundant in diploid than in triploid fish. Cells expressing the myogenic regulatory factor myf-6, a marker of satellite cells committed to differentiation, represented 14.8 % of total myonuclei in diploids and 12.5 % in triploids. At ambient temperatures, the number of white muscle fibres in normal-sex-ratio fish increased more than 30-fold between the alevin and smolt stages, and approximately 3.5-fold further during the first year of seawater growth. The rate of muscle fibre recruitment in seawater stages was significantly greater in diploid than in triploid fish, reaching 1162 fibres day-1 and 608 fibres day-1, respectively, in all-female groups 800 days post-hatching. For 42 cm fork-length fish, there were approximately one-third more muscle fibres per myotome in diploid than in triploid groups, 649 878 and 413 619, respectively, for all-female fish. The probability density function of muscle fibre diameters in each fish was estimated using non-parametric smoothing techniques, and the mean densities for diploids (fD) and triploids (fT) were calculated. The peak fibre diameter was approximately 20 (micro)m in all age classes, irrespective of ploidy. Distinct bimodal distributions of muscle fibre diameter were evident in all groups 775 days and 839 days post-hatching, reflecting seasonal cycles of fibre recruitment. fD and fT were compared using a non-parametric bootstrap technique and the reference band representing the null-hypothesis indicated that there was no difference with ploidy. Reference bands for normal-sex-ratio fish at 315 days and 470 days indicated that diploids had a higher percentage of smaller-diameter fibres and that triploid distributions had a thicker right-hand tail. Similar differences in fD and fT of muscle fibre diameters were found for all-female fish, although the statistical evidence was less strong. Reference bands indicated differences in the middle range of the distributions of muscle fibre diameter in fish 620-775 days post-hatch, with triploids having a thicker right-hand tail. Thus, a lower density of satellite cells was associated with reduced rates of fibre recruitment but a compensatory increase in muscle fibre hypertrophy in triploid compared with diploid fish.  (+info)

Sex allocation: At the females' whim. (8/1154)

Experimental studies of wild birds suggest that females have a previously unappreciated ability to control the sex ratio of their offspring in response to variation in sex-specific fitness benefits.  (+info)

  • Current projects are focused on species groups in the United States and Japan with intriguing reproductive traits: parthenogenesis, sex ratio bias, reproductive armaments, and potential reproductive endosymbionts. (umbc.edu)
  • We used a simulation model to examine the effects of dispersal, temperature-dependent juvenile survival and sex determining mechanism (temperature-dependent sex determination (TSD) and genotypic sex determination (GSD)) and their interactions, on range limits in populations extending across a continuous range of air temperatures. (edu.au)
  • One of the major changes that have taken place in India over the last two decades is a significant shift in the sex ratio at birth, as techniques for prenatal sex determination have become more widely available. (princeton.edu)
  • India will have approximately 6.8 million missing female births between 2017 and 2030 because of sex-selective abortions, according to a recently published study. (christianpost.com)
  • The masculinized SBR for India is a direct result of the practice of sex-selective abortions at the national level," explained the researchers, noting that different regions of the country vary on when this male birth preference began. (christianpost.com)
  • Earlier this month, a three-judge panel of the U.S. Court of Appeals for the Eighth Circuit issued a ruling allowing Arkansas to enforce a law passed in 2017 banning sex-selective abortions. (christianpost.com)
  • The Guttmacher Institute, a research organization with historic ties to Planned Parenthood, has argued that banning sex-selective abortions would not resolve the issues they create. (christianpost.com)
  • Furthermore, the sparse literature does not address the relationship between fertility, spacing and the demand for sex selective abortions, which may lead to biased estimates. (princeton.edu)
  • Using data from the three rounds of the National Family and Health Survey this paper relies on the observed spacing between births to examine the determinants of the demand for sex selective abortions. (princeton.edu)
  • We use the universe of birth and death registry data from Taiwan and exploit plausibly exogenous variation in the availability of sex-selective abortion caused by the legalization of abortions to identify the causal effects of sex-selective abortion on sex ratios at birth and excess female mortality. (cepr.org)
  • Many countries with 'deficits' in their female population see banning sex-selective abortion as a way to curb the observed sex imbalance without discussing potentially negative unintended consequences of this ban on female survival rates as parents may be forced to substitute post-natal for pre-natal sex-selection. (cepr.org)
  • We hypothesised that the unexpected outcome of the 2016 US presidential election may have been a societal stressor for liberal-leaning populations and thereby precipitated such an effect on the sex ratio in Canada. (bmj.com)
  • This population-based study evaluated all births in Canada's most populous province for each month from April 2010 to October 2017, thereby enabling comprehensive assessment of the pattern of changes in the sex ratio in this population. (bmj.com)
  • These signatures likely result from the biased transmission of the driver and selection on the suppressor for the maintenance of equal sex ratios. (genetics.org)
  • Suppressors have been identified in a wide variety of meiotic drive systems and are predicted to be strongly favored by natural selection for the maintenance of equal sex ratios (reviewed by J aenike 2001 ). (genetics.org)
  • Furthermore, the evolution of linked enhancer genes may enable drivers to evade suppression, setting off another bout of Fisherian selection for equal sex ratios ( H artl 1975 ). (genetics.org)
  • To survive, a driver must maintain tight linkage with an insensitive target locus lest it drive against itself, a condition ensured by the lack of recombination between sex chromosomes ( C harlesworth and H artl 1978 ). (genetics.org)
  • Results In the 12 months following the election, the lowest sex ratio occurred in March 2017 (4 months post election). (bmj.com)
  • In 2014, former President Jimmy Carter told David Letterman in an interview that he considered sex-selective abortion the "worst human rights abuse on earth. (christianpost.com)
  • X-linked (or Y-linked) meiotic drive elements reduce the transmission of the Y (X) chromosome and skew progeny and population sex ratios, leading to intense conflict among genomic compartments. (genetics.org)
  • While drive elements may arise on any chromosome, sex-linked drivers have higher population invasion probabilities than autosomal drivers and are more easily detected due to their impact on progeny sex ratios ( H urst and P omiankowski 1991 ). (genetics.org)
  • Drosophila is the most extensively studied insect taxon, and sex-chromosome meiotic drive systems have been identified in more than a dozen species ( J aenike 2001 ). (genetics.org)
  • Jonathan Abbamonte, research analyst at the Population Research Institute, wrote in an op-ed piece published by The Christian Post last year that India is not the only nation facing a disproportionately high number of male births due to sex-selective abortion. (christianpost.com)
  • This population-based analysis cannot ascertain an individual woman's political preferences or whether her perception of the election outcome contributed to fetal loss and thereby impacted the sex ratio. (bmj.com)
  • Two-sex dispersal eliminated the influence of biased sex ratios on ranges.Conclusion: The results highlight the importance of the demographic parameter of sex ratio in determining population persistence and species range limits. (edu.au)
  • Compared with the preceding months, the sex ratio was lower in the 5 months from March to July 2017 (p=0.02) during which time it was rising (p=0.01), reflecting recovery from the nadir. (bmj.com)
  • Both effects were seen in liberal-leaning regions of Ontario (lower sex ratio (p=0.006) and recovery (p=0.002) in March-July 2017) but not in conservative-leaning areas (p=0.12 and p=0.49, respectively). (bmj.com)
  • Here, we characterize naturally occurring genetic variation at the Winters sex-ratio driver ( Distorter on the X or Dox ), its progenitor gene ( Mother of Dox or MDox ), and its suppressor gene ( Not Much Yang or Nmy ), which have been previously mapped and characterized. (genetics.org)
  • Obviously, a complete sweep of a sex-linked driver dooms a male-less (or female-less) population to extinction ( H amilton 1967 ), and natural selection strongly favors genetic factors that suppress drive and restore Mendelian segregation. (genetics.org)
  • The ecological study design enabled evaluation of this population outcome (sex ratio) and its precise monthly pattern in the year following the 2016 US presidential election, while accounting for seasonal changes therein. (bmj.com)
  • In India alone, I have found that approximately 15.8 million girls have been eliminated through sex-selective abortion and other forms of prenatal daughter elimination since 1990," he wrote in 2019. (christianpost.com)
  • In the United States, several states have considered and even passed bans on sex-selective abortion, only to face legal battles over their constitutionality by pro-choice groups. (christianpost.com)
  • Background: Geographic ranges of ectotherms such as reptiles may be determined strongly by abiotic factors owing to causal links between ambient temperature, juvenile survival and individual sex (male or female). (edu.au)
  • None of the Winters sex-ratio genes are fixed in D. simulans , and at all loci we find ancestral alleles, which lack the gene insertions and exhibit high levels of nucleotide polymorphism compared to the derived alleles. (genetics.org)
  • We discuss the possible causes of the maintenance of presence-absence polymorphism in the Winters sex-ratio genes. (genetics.org)