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PubMed1978

The identification of the social sex-role stereotypes.

The purpose of this study was to identify the social sex-role stereotypes that exist in the nation. The hypothesis for this study was that the stereotypes for femininity and masculinity are dimorphous. To determine the extent of dimorphism, four social sex-role stereotypes were examined: masculine men, feminine women, feminine men, and masculine women. Three hundred female and male respondents from all regions of the nation, who varied in age, ethnicity, education, sexual orientation, and social sex-role, completed a questionnaire by listing the characteristics people expected a masculine man, a feminine woman, a feminine man, and a masculine woman to have. The results supported the hypothesis that the stereotypes for femininity and masculinity are dimorphous.

Adult↗
PubMed2003

[Frequency of altered male factor in an infertility clinic].

UNLABELLED: Infertility is the incapacity of a couple to conceive after a year of regular sexual life without using a method for family planning. The infertility state is dependent on the female factor as well as masculine factor; an altered masculine factor is designated when any cause or causes of infertility reside in the male. The masculine factor as a cause of infertility is present in 40 to 50% of cases hence the importance of an integral evaluation of male alterations and its fertility. The World Health Organization (WHO) has proposed to classify the masculine infertility based on semen features. OBJECTIVE: To determine the frequency of the masculine factor altered in association to diagnosed abnormalities, according to the number of affected seminal indexes based on seminograms performed in infertile patients seen at the department of Human Reproductive Medicine, Hospital Juárez de México. MATERIAL AND METHODS: An observational, descriptive, transverse, retrospective study was performed. SUBJECTS: the seminograms practiced were reviewed from 571 clinical files of couples that the consultation for infertility from January 1993 to February 2001. Collection and analysis of semen samples was based on standards settled by WHO. RESULTS: Of 571 seminogram informs, 371 (65%) showed alterations in the seminal indexes, the stocking of age of this group was of 31.89 years +/- SD 6.3 years. Our findings were: azoospermia in 89 (23.98%), astenonecrozoospermia in 44 (11.85%), hypospermia in 43 (11.59%), astenozoospermia in 33 (8.89%), oligoastenozoospermia in 31 (8.35%) hyponecrozoospermia in 30 (8.08%), oligozoospermia in 25 (6.73%), others in 21 (5.7%), necrozoospermia in 19 (5.12%), hypoastenozoospermia in 18 (4.85%), cryptozoospermia in 11 (2.97%), and hypooligoastenozoospermia in 7 (1.88%). In 62.6% of seminograms practiced there was an isolated alteration, in 34.4% two alterations and in the remaining 3% more than two alterations. CONCLUSION: We found masculine factor altered in 65% of couples who were requiring consultation for infertility. The three main alterations of seminal indexes were azoospermia, astenonecrozoospermia and hypospermia.

Adolescent↗
PubMed2004

Comparison of anterior instrumentation systems and the results of minimum 5 years follow-up in the treatment of tuberculosis spondylitis.

Anterior debridement, strut grafting and instrumentation have an increasing popularity in the treatment of tuberculosis of spine. Anterior fixation can be done either by a plate or a rod system. This study reports on the surgical results of 59 patients with Pott's disease that had anterior radical debridement and anterior fusion and anterior instrumentation with 5 years follow-up. Average age at the time of operation was 46.3+/-13.5 years. Average follow-up was 84.6+/-11.3 months. Local kyphosis was measured as the angle between the upper and lower end plates of the collapsed vertebrae preoperatively, postoperatively and at the last follow-up visit. Vertebral collapse, destruction, cold abscess, and canal compromise were assessed in MR images. The indication for surgery was either one of the deformity, instability or neurological compromise. Surgical treatment included anterior radical debridement followed by grafting with tricortical auto graft and anterior instrumentation at levels just above and below the diseased segment(s) with either plate (Sofamor-Danek, Z plate, Group A) or rod (Sofamor-Danek, CDH, Group B) systems. There were 23 patients in group A and 36 patients in group B. All patients had similar anti tuberculosis chemotherapy. Patients had similar rehabilitation program after the surgery. The deformity in the sagittal and the coronal plane was measured and presence of significant consolidation, along with the absence of implant failure or correction loss was considered as signs of fusion. The two groups were similar according to age (46.9+/-14.2 vs. 45.8+/-13.1), gender, average number of involved levels (1.8+/-0.5 vs. 1.6+/-0.5), location of involved levels, severity of deformity (21.5 degrees+/-9.9 masculine vs. 24.8 degrees+/-11.9 masculine) and type of autografts (p>0.05 for all parameters). 39.1 % of patients in group A and 41.6 % of patients in group B had neurological compromise with improvement in majority at the end of follow-up. Deformities were corrected to 5.2 degrees+/-5.7 masculine in group A and 6.1 degrees+/-6.8 masculine in group B with no significant difference. At the time of latest follow-up there were 1.7 degrees+/-2.0 masculine correction loss in group A and 1.4 degrees+/-1.9 masculine in group B with no significant difference in between two groups (p>0.05). Overall, it was observed that, the addition of anterior instrumentation increased the rate of correction of the kyphotic deformity (78.5+/-20.5%), and was effective in maintaining it with an average loss of 1.5 degrees+/-1.9 degrees. Of the 24 (44.1%) patients with neurological symptoms, 20 (83.3%) had full and 4 (16.7%) partial recoveries. There was no apparent pseudoarthrosis and implant failure in both groups and all patients demonstrated clinical improvement in tuberculosis infection without recurrences and reactivation. Four major complications occurred in the group A (major vessel complication: 3.4%, secondary non-specific infection: 3.4%). Disease reactivation was not seen with the employment of an aggressive chemotherapy regimen. It was concluded that anterior instrumentation is a safe and effective method in the treatment of tuberculosis spondylitis. There were no significant differences between the two instrumentation systems in terms of sagittal alignment reconstruction and fusion rate. In rod-screw systems, the disadvantages of scoliotic deformity correction through frontal plan in plate performing did not occur and it is though to have the advantage of long instrumentation in multiple level deformities.

Adult↗
PubMedDate not supplied

Sex-role identity and image of nursing of females at two levels of baccalaureate nursing education.

Ninety-two female nursing students, 56 at entry (ENTL) to and 36 at exit (EXTL) from the baccalaureate program, participated in an investigation of the relationship between sex-role identity and image of nursing. Bem's Sex Role Inventory, which allows subjects to receive both masculinity and femininity scores, was used to categorize subjects as masculine, androgynous, feminine, or undifferentiated. Frank's Image of Nursing Questionnaire was used to evaluate subjects' image of nursing. Study purposes were to: compare the sex-role identity of nursing students and general college females, compare the image of nursing held by nursing students with the image advanced by the profession, determine the relationship between sex-role categorization and image of nursing, and determine the relationship between level of endorsement of masculine and feminine characteristics and image of nursing. Analyses indicated: a significant (p < .05) difference in sex-role identity based on categorization between the total nurse sample and general college females, EXTL students endorsed more masculine characteristics than ENTL students (p < .003), EXTL students endorsed more feminine characteristics than general college females (p < .001), ENTL and EXTL students and Frank's judges held significantly different images of nursing (p < .01 for all comparisons), and significant correlations between the image of nursing and level of endorsement of masculine characteristics, not masculine role identity, for EXTL (p < .002) and total nurse (p < .001) samples.

Education, Nursing, Baccalaureate↗
PubMedDate not supplied

Male facial appearance signals physical strength to women.

Previous studies showed that male faces with extreme features that are likely to be associated with testosterone (T) are perceived as dominant and masculine. Women were reported to prefer masculinized male faces, as they may consider T markers to be an "honest" indication of good health. However, it is also likely that female preferences for certain male faces arise from the fact that dominant- and masculine-looking males are signaling characteristics which may be beneficial in intrasexual conflict, and thereby also indicate potential achievers of high status, an important factor in female mate selection. Although numerous studies were built on this assumption, nothing is known about the relationship between perceived facial dominance and physical strength in men. We measured hand-grip strength, as a measure of overall physical strength, in a sample of 32 male students, and recorded age, body weight, and height. Seventy-nine women rated facial images of these men for dominance, masculinity, and attractiveness. After controlling for age and body weight, hand-grip strength was found to correlate significantly positively with all three measures. The present data thus support the supposition that a male's physical strength is also signaled via facial characteristics of dominance and masculinity, which are considered attractive by women.

Adolescent↗
PubMed2001

Search for genes involved in the temperature-induced gonadal sex differentiation in the tilapia, Oreochromis niloticus.

In the tilapia, Oreochromis niloticus, sex is determined by genetic factors (XX/XY) but temperature can also influence the gonadal sex differentiation. Elevated temperatures of 35 degrees C can generate functional male phenotypes if applied before and during sexual differentiation. The genes and mechanisms by which temperature acts on the cascade leading to sex differentiation have been investigated. Two strategies have been followed: 1) Search for novel genes by differential display, and 2) Expression studies of candidate genes. Genetically all-female and all-male progenies were reared at 27 degrees C (natural temperature) and at 35 degrees C (masculinizing treatment) and gonads dissected. Using differential display, we isolated a 300 bp cDNA (MM20C) from temperature-masculinized females. Virtual northern analysis revealed a 1.2 kb transcript in 35 degrees C treated females and males, but hardly any expression in natural females (27 degrees C). Semi-quantitative RT-PCR established a several-fold increase in MM20C expression in 35 degrees C masculinized fry. Elevated expression was observed in natural males (27 degrees C) with higher levels detected in those reared at 35 degrees C. Furthermore, we have analyzed as a candidate gene the P450 11beta-hydroxylase, an important androgen steroidogenic enzyme. Low levels of expression were found in natural males. This coincides with low concentrations of 11 ketotestosterone in the gonads before and during gonadal sex differentiation. Higher expression levels of 11beta-hydroxylase were detected in male gonads at 35 degrees C but levels in phenotypic males were similar to those found for natural females. Previous results reported that expression of aromatase is repressed by masculinizing treatments. Our study demonstrated that masculinizing-temperature can also stimulate the expression of other gene(s).

Animals↗
PubMed1991

Tamoxifen's effects on the zebra finch song system are estrogenic, not antiestrogenic.

Antiestrogens fail to block the masculine ontogeny of the zebra finch song system that is hypothesized to occur as a result of early estrogen action. Moreover, they hypermasculinize the male, and masculinize the female song systems. In experiment 1, we assessed whether these antiestrogenic effects might mimic estrogenic actions. Zebra finch chicks received one of two treatments. They were given estradiol benzoate (EB) or vehicle daily for the first 20 days after hatching and sacrificed at 60 days of age, or they received EB or vehicle for the first 25 days after hatching, at which time they were sacrificed. In the day 60 group, certain attributes of the song system were hypermasculinized in males and masculinized in females by EB, when compared with controls. In the day 25 group, males treated with EB were partially demasculinized, while the females were partially masculinized. In experiment 2, we assessed whether simultaneous treatment with tamoxifen was capable of antagonizing the effects of EB obtained in experiment 1 (day 60 group). Sixty-day-old females, previously treated with both EB and tamoxifen for the first 20 days after hatching, had more masculine song regions than females treated with either EB alone or tamoxifen alone. In males, the effects of the combined treatment of EB and tamoxifen over those produced by tamoxifen alone were not as dramatic as in the female. These results are similar to those obtained in systems where tamoxifen is purely estrogenic and suggest that in the song system, tamoxifen acts as an estrogen, not an antiestrogen.

Animals↗
PubMed1994

Cross-gender identity in transvestites and male transsexuals.

A self-theory of transvestism and secondary transsexuality in which gender identity is a major self subsystem has been advanced in previous research. Within this framework transsexuals and transvestites were compared on a number of developmental characteristics. While early-onset transsexuals (n = 103) were dominantly female, both late-onset transsexuals (n = 52) and transvestites (n = 36) showed much more feminine behavior than expected. This was interpreted as a sign that they were already developing a feminine gender identity in their early years. Implications for this theory were discussed: (i) The assumption of two gender identity subsystems (a masculine and a feminine) in any human being, which can have any relative strength; (ii) the incorporation of the concept of expression of an identity subsystem, which can be unconditional or conditional (i.e., expression of aspects of the self only if certain conditions are fulfilled) and which has the function of self-seeking. Two continua are proposed. One ranges from a strong feminine gender identity subsystem that is unconditionally expressed to weak unexpressed femininity. The second ranges from a strong and unconditionally expressed masculinity to a weak masculinity. Male-to-female transsexuals (and "normal" females) are characterized by a strong unconditionally expressed feminine gender identity in combination with a weak unexpressed masculinity. Transvestism is a position in between in which both masculinity and femininity are conditionally expressed.

Adolescent↗
PubMed2005

Haptic shape discrimination in humans: insight into haptic frames of reference.

This study investigates how a change in the physical relation between objects (two-dimensional, 2-D, angles) and a subject, as well as scanning conditions, modify the ability to discriminate small changes in 2-D shape. Subjects scanned pairs of angles (90 masculine standard; 91 masculine-103 masculine comparison angles) with the right index finger of the out-stretched arm, identifying the larger of each pair. When joint rotation was restricted to the shoulder, the discrimination threshold significantly increased when the angles were explored with the shoulder in a more eccentric position rather than closer to the midline (60 masculine versus 30 masculine to the right). This result was attributed to changes in proprioceptive sensitivity, since explorations restricted to distal joints (wrist/second metacarpophalangeal joint) showed no change with shoulder position. The results showed, moreover, that discrimination threshold was similar for distal and proximal joints when the delay between scanning the pairs of angles was long (15 s). This observation suggests that regional variations in proprioceptive acuity (proximal>distal) may reflect an adaptation to generate an invariant central representation of haptic shape. Using a shorter interscan delay (5 s), a position-dependent increase in discrimination threshold was revealed for distal explorations, an effect that disappeared when the head was turned in the direction of the unseen angle (vision occluded). We suggest that these results can be explained by the existence of two competing egocentric frames of reference with different time courses, one of short duration that is centred on the arm/hand, and a second of longer duration centred on the head. At the short delay, the reference frames interacted to distort the haptic representation when they were misaligned. This distortion was resolved at the long delay, possibly through suppression of the arm/hand-centred reference frame.

Adult↗
PubMed1988

Paradoxical hypermasculinization of the zebra finch song system by an antiestrogen.

Exogenous estrogens, when administered to hatchling female zebra finches, masculinize the morphology and function of their neural vocal control system. The first of two experiments evaluated whether tamoxifen citrate is an antiestrogen in zebra finches, and the second determined whether it would block the masculinization hypothesized to be caused in hatchling males by the males' endogenous estradiol. In the first experiment adult female zebra finches were ovariectomized and injected for 10 days with estradiol benzoate (EB), tamoxifen, EB and tamoxifen combined, or vehicle (control). The dependent variable was oviduct weight. The EB-stimulated growth of the oviduct was blocked by tamoxifen, which had no effects when administered alone. Thus, tamoxifen acts as an antiestrogen in the zebra finch oviduct. In Experiment 2, male and female zebra finches were treated with tamoxifen or vehicle for the first 20 days after hatching. The males were castrated at 20 days. At 60 days we compared the song control regions of experimental and control males and females. In both sexes tamoxifen increased the somatic areas of neurons in RA (robust nucleus of the archistriatum), HVc (caudal nucleus of the ventral hyperstriatum), and MAN (magnocellular nucleus of the anterior neostriatum). Tamoxifen also increased the volumes of HVc, RA, MAN, and Area X in males. Thus, tamoxifen failed to block masculinization of males, but masculinized females and hypermasculinized males. Tamoxifen's hypermasculinization of the male and masculinization of the female song system is paradoxical given that (1) estradiol does not have similar effects on the male song system, and (2) tamoxifen antagonizes the effects of EB in the oviduct.

Animals↗
PubMed1993

The effect of prenatal stress on adult sexual behavior in rats depends on the nature of the stressor.

It is well known that prenatal stress induces behavioral demasculinization and/or feminization in male offspring during adulthood. In this study, four different stressors were prenatally applied to rats. Pregnant rats were subjected to immobilization, unavoidable electric foot shocks, rapid eye movement sleep deprivation (REMd), or immersion in cold water. During adulthood, male offspring were tested for masculine and feminine sexual behavior. The results corroborated the fact that immobilization induced an impairment of masculine sexual behavior and a facilitation of feminine sexual behavior. Electric shocks showed only minor differences in masculine behavior when compared to intact controls, and no signs of lordosis behavior were observed. The REMd group displayed a major impairment of masculine behavior, even greater than that observed within the immobilization group. However, lordosis behavior was only induced with estradiol. On the other hand, water immersion seems to have a facilitatory effect on several parameters of masculine behavior and did not show lordosis behavior even with hormonal treatment. These results strongly suggest that changes in sex behavior induced by prenatal stress are linked to the nature of the stressor.

Animals↗
PubMed1985

Personality indicators of psychosocial adjustment in first-year medical students.

One aspect of the Rush Medical College Longitudinal Study is concerned with the identification of personality traits that predict various kinds of psychosocial adjustments and impairments among medical students and physicians. Two orthogonal traits, masculinity and femininity, were selected for study as independent variables because of their implications for mental health and their relevance to the work of physicians. Ninety percent (N = 106) of a class of first-year medical students completed measures of masculinity and femininity during orientation and, 8 months later, completed a broad array of dependent measures of psychological well-being, interpersonal satisfaction, humanistic attitudes and alcohol consumption. Analyses of the data revealed strong and consistent main effects of masculinity on depression, confidence, pleasure capacity, extraversion, locus of control, neuroticism and interpersonal satisfaction. Femininity was associated with depression, pleasure capacity, extraversion, neuroticism, interpersonal satisfaction, concern for the opinion of others and humane attitudes toward patient care. Low femininity was also associated with high alcohol consumption. These results suggest that masculinity and femininity scores may help to identify at the outset medical students at risk for impairment, and that androgynous individuals (who are high in both masculinity and femininity) may be especially well-suited to assume the demanding and varied roles that physicians are called on to play.

Adaptation, Psychological↗
PubMed1990

Congenital adrenal hyperplasia. I: Gender-related behavior and attitudes in female patients and sisters.

Thirty-five female patients with congenital adrenal hyperplasia (CAH) were compared to a group of 16 healthy sisters in regard to gender-related behavioral patterns, present attitudes, and plans for the future. A semi-structured interview with the subjects, ages 11 to 41 yr, and their mothers concentrated on four to five age stages. Results of retrospective data from single items as well as from several related composite scales ("interests and behavior," "appearance," "overall scores") revealed significant group differences: Both in mother-assessment and self-assessment, CAH patients showed a "more masculine" orientation than their sisters, but this was far from consistent across all age stages, especially for single items. Unexpectedly, the gender-behavior differences between CAH patients and sisters did not hold for certain items and scales of "social behavior" (e.g., assertiveness, dominance, acceptance in peer groups) and, in contrast to some of the existing literature, also not for "high-energy expenditure." With regard to expectations for the future, CAH patients had less of a "wish to have their own children" and a higher preference for "having a career versus staying at home." Age, socioeconomic status, intelligence, and presence or absence of a sister as possibly intervening psychosocial/demographic factors could not explain the group differences in behavior. Degree of genital masculinization (Prader stages) or "onset and quality" of therapy as measures of pre- and postnatal androgenization, respectively, could also not account for the degree of the "more masculine" orientation in the CAH group. Nevertheless, the overall results are compatible with earlier findings on the masculinizing effects of prenatal androgens on behavior in humans and point to a time period after sexual differentiation of the genitalia and before birth as the most likely one for the effects of prenatal hormones on behavioral masculinization in humans.

Adaptation, Psychological↗
PubMed2005

Gender role orientations and alcohol use among Moscow and Toronto adults.

Using self-report data from representative community samples of Moscow and Toronto adults, we examine the effects of sex, masculinity, and femininity on alcohol use. Consistent with prior research, our results show that men in Moscow and Toronto drink significantly more than women; women in both samples tend more toward conventional femininity than men; and masculinity levels are greater among Toronto men relative to Toronto women. Moscow men and women, however, show comparable masculinity levels. Neither masculinity nor femininity explains the sex gap in alcohol use in either sample. However, sex- and sample-specific effects are identified. In Toronto, femininity is associated with higher alcohol use among women. In Moscow, masculinity is associated with lower use among men and higher use among women. The findings provide preliminary support for our assertion that the characteristics of national contexts, such as drinking norms and "Soviet-style socialism" [Cockerham, Snead, and Dewaal (2002). Journal of Health and Social Behavior, 43, 42-55] interact with traditional gender role orientations to influence alcohol use patterns. We suggest that a movement toward culturally sensitive policies that consider sex-specific social expectations and responses may contribute to improved health outcomes across nations.

Adolescent↗
PubMed1998

Long-term effects of childhood maltreatment history on gender-related personality characteristics.

OBJECTIVE: The aim of the study was to test the hypothesis that different types of gender-related personality attributes are associated with a past history of different types of childhood maltreatment. METHOD: A survey was administered to 1,060 male soldiers and 305 female soldiers in the U.S. Army. The survey instrument included the Extended Personal Attributes Questionnaire (EPAQ) which is a self-assessment instrument of personality characteristics associated with gender, and includes measures of positive masculinity (self-assertive/instrumental traits), positive femininity (expressive/interpersonal traits), negative masculinity (hyper masculine/macho traits), and negative femininity (subordination of self to others). The survey instrument also included the Childhood Trauma Questionnaire (CTQ), which contains scales measuring sexual abuse, physical-emotional abuse, physical neglect, and emotional neglect, and four questions on childhood sexual abuse developed for a national survey of U.S. adults. RESULTS: Negative masculinity was predicted by male gender, younger age, and childhood physical-emotional abuse. Negative femininity was predicted by physical-emotional abuse and sexual abuse. The relationship to sexual abuse was mainly evident for males. Positive femininity was positively correlated with sexual abuse for females and negatively correlated with sexual abuse for males. Positive masculinity was negatively correlated with emotional neglect for males but not for females. Positive femininity was negatively correlated with emotional neglect for both genders. CONCLUSIONS: Childhood abuse was associated with the presence of negative gender-related attributes; childhood neglect was associated with absence of positive gender-related attributes. Childhood physical abuse was associated with negative masculine attributes in both genders. Childhood sexual abuse was associated with positive feminine attributes in females, and negative feminine attributes in males. The finding for females is counterintuitive, and is discussed in the light of the clinical literature on certain types of adaptation to incest.

Adult↗
PubMed1986

Interaction of sex role self-concept with relationship quality and relationship beliefs in married, heterosexual cohabiting, gay, and lesbian couples.

The relation between sex role self-concept (masculine, feminine, undifferentiated, and androgynous) and both relationship quality and dysfunctional relationship beliefs was examined in 370 monogamous partners who represented four types of couples (married, heterosexual cohabiting, gay, and lesbian). Analyses used both the individual partner and the couple as the unit of analysis. The individual partner analyses revealed that relationship quality and relationship beliefs differed by subjects' sex role self-concept. Androgynous and feminine subjects reported higher relationship quality than masculine and undifferentiated subjects; androgynous subjects had fewer "disagreement is destructive" beliefs than feminine subjects; and androgynous subjects had fewer "partner cannot change" beliefs than undifferentiated subjects. The couple analyses revealed a relation between partners' sex role self-concept only for the heterosexual cohabiting couples. For these couples, masculine men tended to pair with feminine or undifferentiated women, and androgynous partners tended to pair together. Relative to other couples, couples in which one or both partners were androgynous or feminine reported the highest relationship quality, whereas couples in which one or both partners were undifferentiated or masculine reported the lowest relationship quality. These effects did not vary by type of couple. The study concluded that sex role self-concept is a robust factor in appraisals of relationship quality. Relative to masculine and undifferentiated individuals, androgynous and feminine individuals report greater positive relationship functioning.

Adult↗
PubMed1999

Gender congruence in confirmatory and compensatory drinking.

The relationship between gender-stereotypical traits and drinking behaviors was examined in 422 university students via both positive and negative measures of masculinity and femininity. Two canonical variates summarized the underlying relationships. The 1st canonical variate indicated that both high negative masculinity and low positive femininity predicted alcohol consumption and alcohol-related problems. This behavior was labeled confirmatory drinking because it depicts a style of drinking that reinforces gender-stereotypical images about alcohol use; masculine characteristics are typically associated with high levels of alcohol consumption. The 2nd canonical variate indicated that both low positive masculinity and low positive femininity predicted problem drinking. This behavior was labeled compensatory drinking because drinkers often use alcohol to express their masculinity and femininity. The distinction between confirmatory and compensatory drinking has important implications for the development of more effective education and preventative strategies.

Adult↗
PubMed2002

Ancient sex-specific extension of the cytochrome c oxidase II gene in bivalves and the fidelity of doubly-uniparental inheritance.

Bivalves of the families Mytilidae and Unionidae show a unique mode of mitochondrial DNA inheritance called doubly uniparental inheritance. In addition to receiving the maternally transmitted mtDNA lineage, males receive a separate mtDNA genome from their fathers. This system is sometimes compromised, in that female genomes are occasionally recruited into the male cycle of inheritance. These masculinization events are common in the Mytilidae but have not been reported in the Unionidae. In order to estimate the age of the male and the female lineages in the Unionidae and to look for evidence of masculinization, we sequenced the junction between the cytochrome c oxidase II gene and the cytochrome c oxidase I gene. The unionid male and female lineages diverged approximately 450 MYA. There is no evidence for masculinization during this period, suggesting that there are taxon-specific differences in the rate of masculinization. Coincidentally, a 200-codon extension of the COII gene is present in the male genome of the Unionidae and may be responsible for the absence of masculinization.

Amino Acid Sequence↗