Showing papers by "La Trobe University published in 1995"

Culture, gender, and self: A perspective from individualism-collectivism research.

Abstract: Individualism and collectivism are often equated with independent vs. interdependent, agentic vs. communal, and separate vs. relational self-construals. Although these same concepts have been used to characterize both cultural and gender differences, a perspective of cultural evolution suggests it is unlikely. A division of labor within society may produce gender differences, but this cannot explain cultural differences. A study of self-construal involving 5 cultures (Australia, the United States, Hawaii, Japan, and Korea) shows that differences between these cultures are captured mostly by the extent to which people see themselves as acting as independent agents, whereas gender differences are best summarized by the extent to which people regard themselves as emotionally related to others.

Identifying effective psychological treatments for insomnia: A meta-analysis.

Abstract: Insomnia is a debilitating and widespread complaint. Concern over the iatrogenic effects of pharmacological therapies has led to the development of several psychological treatments for insomnia. To clarify the effects of these treatments, 66 outcome studies representing 139 treatment groups were included in a meta-analysis. The results indicated that psychological treatments produce considerable enhancement of both sleep patterns and the subjective experience of sleep. In terms of enhancing sleep onset, active treatments were all superior to placebo therapies but did not differ greatly in efficacy. Greater therapeutic gains were available for participants who were clinically referred and who were not regular users of sedative hypnotics. Future research directions are suggested.

A far ultraviolet imager for the International Solar-Terrestrial Physics Mission

Abstract: The aurorae are the result of collisions with the atmosphere of energetic particles that have their origin in the solar wind, and reach the atmosphere after having undergone varying degrees of acceleration and redistribution within the Earth's magnetosphere. The global scale phenomenon represented by the aurorae therefore contains considerable information concerning the solar-terrestrial connection. For example, by correctly measuring specific auroral emissions, and with the aid of comprehensive models of the region, we can infer the total energy flux entering the atmosphere and the average energy of the particles causing these emissions. Furthermore, from these auroral emissions we can determine the ionospheric conductances that are part of the closing of the magnetospheric currents through the ionosphere, and from these we can in turn obtain the electric potentials and convective patterns that are an essential element to our understanding of the global magnetosphere-ionosphere-thermosphere-mesosphere. Simultaneously acquired images of the auroral oval and polar cap not only yield the temporal and spatial morphology from which we can infer activity indices, but in conjunction with simultaneous measurements made on spacecraft at other locations within the magnetosphere, allow us to map the various parts of the oval back to their source regions in the magnetosphere. This paper describes the Ultraviolet Imager for the Global Geospace Sciences portion of the International Solar-Terrestrial Physics program. The instrument operates in the far ultraviolet (FUV) and is capable of imaging the auroral oval regardless of whether it is sunlit or in darkness. The instrument has an 8° circular field of view and is located on a despun platform which permits simultaneous imaging of the entire oval for at least 9 hours of every 18 hour orbit. The three mirror, unobscured aperture, optical system (f/2.9) provides excellent imaging over this full field of view, yielding a per pixel angular resolution of 0.6 milliradians. Its FUV filters have been designed to allow accurate spectral separation of the features of interest, thus allowing quantitative interpretation of the images to provide the parameters mentioned above. The system has been designed to provide ten orders of magnitude blocking against longer wavelength (primarily visible) scattered sunlight, thus allowing the first imaging of key, spectrally resolved, FUV diagnostic features in the fully sunlit midday aurorae. The intensified-CCD detector has a nominal frame rate of 37 s, and the fast optical system has a noise equivalent signal within one frame of ∼ 10R. The instantaneous dynamic range is >1000 and can be positioned within an overall gain range of 104, allowing measurement of both the very weak polar cap emissions and the very bright aurora. The optical surfaces have been designed to be sufficiently smooth to permit this dynamic range to be utilized without the scattering of light from bright features into the weaker features. Finally, the data product can only be as good as the degree to which the instrument performance is characterized and calibrated. In the VUV, calibration of an an imager intended for quantitative studies is a task requiring some pioneering methods, but it is now possible to calibrate such an instrument over its focal plane to an accuracy of ±10%. In summary, very recent advances in optical, filter and detector technology have been exploited to produce an auroral imager to meet the ISTP objectives.

The origin and function of the mammalian Y chromosome and Y-borne genes – an evolving understanding

Abstract: Mammals have an XX:XY system of chromosomal sex determination in which a small heterochromatic Y controls male development. The Y contains the testis determining factor SRY, as well as several genes important in spermatogenesis. Comparative studies show that the Y was once homologous with the X, but has been progressively degraded, and now consists largely of repeated sequences as well as degraded copies of X linked genes. The small original X and Y have been enlarged by cycles of autosomal addition to one partner, recombination onto the other and continuing attrition of the compound Y. This addition-attrition hypothesis predicts that the pseudoautosomal region of the human X is merely the last relic of the latest addition. Genes (including SRY) on the conserved or added region of the Y evolved functions in male sex determination and differentiation distinct from the general functions of their X-linked partners. Although the gonadogenesis pathway is highly conserved in vertebrates, its control has probably changed radically and rapidly in vertebrate--even mammalian--evolution.

Comparison of Asperger syndrome and high-functioning autistic children on a Test of Motor Impairment

Abstract: Compared the motor impairment levels of Asperger syndrome and high functioning autistic children using a standardized test, the Test of Motor Impairment-Henderson Revision. The two groups did not differ on either total or subscale impairment scores. Intelligence level was negatively correlated with motor impairment although the relationship was mostly accounted for by the Asperger children. There was considerable variability within both clinical groups but 50% of Asperger children and 67% of autistic children showed a clinically significant level of motor impairment. Results offer no support for clumsiness as a diagnostically differentiating feature of these disorders.

Sex determination and population biology in the hymenoptera

Abstract: The Hymenoptera (ants, bees, wasps and sawflies) display a great variety of social systems and sex ratios and have played a key role in the development and testing of many evolutionary models. Traditionally, considerable emphasis was placed on the fact that hymenopterans have haploid males and diploid females but it is now clear that many species also regularly produce sterile, diploid males. Recent studies explore the diverse ways in which production of these diploid males influences selection on mating systems, sex ratios and social behaviour.

The sleep/wake rhythm in children with autism

Abstract: The sleep patterns of two groups of children with autism, one with moderate to severe intellectual handicap, and one with mild handicap to normal IQ level, were compared with those of children without autism. Parents completed 14 day sleep diaries and questionnaires. Results suggested that at some stage during childhood, particularly under 8 years of age, the majority of children with autism will experience sleep problems. These problems are likely to be severe in many cases and will generally include one or more of: extreme sleep latencies; lengthy periods of night waking; shortened night sleep; and early morning waking. Such problems may have some specificity for autism as they appear to be rare in non-handicapped children and in children with mild degrees of intellectual handicap. It is likely that sleep problems in early childhood are related to the severe social difficulties present in autism and the consequent inability of these children to use social cues to synchronise their sleep/wake cycle. Continued sleep difficulties at older ages and with higher IQ may also be related to arousal and anxiety factors.

Effects of creatine phosphate and P(i) on Ca2+ movements and tension development in rat skinned skeletal muscle fibres.

Abstract: 1. Mechanically skinned fast-twitch (FT) and slow-twitch (ST) muscle fibres of the rat were used to investigate the effects of fatigue-like changes in creatine phosphate (CP) and inorganic phosphate (P(i)) concentration on Ca(2+)-activation properties of the myofilaments as well as Ca2+ movements into and out of the sarcoplasmic reticulum (SR). 2. Decreasing CP from 50 mM to zero in FT fibres increased maximum Ca(2+)-activated tension (Tmax) by 16 +/- 2% and shifted the mid-point of the tension-pCa relation (pCa50) to the left by 0.28 +/- 0.03 pCa units. In ST fibres, a decrease of CP from 25 mM to zero increased Tmax by 9 +/- 1% and increased the pCa50 by 0.16 +/- 0.01 pCa units. The effect of CP on Tmax was suppressed in both fibre types by prior treatment with 0.3 mM FDNB (1-fluoro-2,4-dinitrobenzene), suggesting that these effects may occur via changes in creatine kinase activity. 3. Increases of P(i) in the range 0-50 mM reduced the pCa50 and Tmax in both fibre types. These effects were more pronounced in ST fibres than in FT fibres in absolute terms. However, normalization of the results to resting P(i) levels appropriate to both fibre types (1 mM for FT and 5 mM for ST fibres) revealed similar decreases in Tmax (approximately 39% at 25 mM P(i) and approximately 48% at 50 mM P(i)) and pCa50 (0.25 pCa units at 25-50 mM P(i)). The depressant action of P(i) on both parameters was considerably reduced when the rise in P(i) was accompanied by an equivalent reduction in [CP]. 4. Tension development in the presence of complex, fatigue-like milieu changes (40 mM P(i) for FT; 20 mM P(i) for ST) was decreased by 35-40% at a constant myoplasmic [Ca2+] of 6 microM in both fibre types. 5. SR Ca2+ loading at a myoplasmic [Ca2+] of 100 nM was found to increase abruptly when the [P(i)] during loading was increased to near 9 mM. At a myoplasmic [Ca2+] of 300 nM, the threshold P(i) for this effect dropped to approximately 3 mM. 6. Tension responses evoked by caffeine in the absence of P(i) were smaller and slower to peak if fibres were exposed to P(i) in a restricted myoplasmic Ca2+ pool after SR Ca2+ loading. This indicated that myoplasmic P(i) can decrease and prolong the rate of Ca2+ release from the SR.(ABSTRACT TRUNCATED AT 400 WORDS)

Prediction of employment status 2 years after traumatic brain injury

Abstract: The present study used a multivariate approach to investigate which of a range of variables relating to demographic factors, injury severity and degree of disability on admission to rehabilitation were the best predictors of employment status 2 years after traumatic brain injury (TBI). Subjects were 74 TBI patients who had been working prior to injury, had undergone rehabilitation at Bethesda Hospital and attended a review clinic 2 years after injury. A cross-validation sample consisted of a further 50 such subjects. Following preliminary analysis four input variables were selected: age under or over 40 at time of injury, Glasgow Coma Scale score on acute hospital admission, duration of post-traumatic amnesia and total score on the Disability Rating Scale (DRS) on admission to rehabilitation. Stepwise discriminant function analysis resulted in a discriminant function consisting of three variables—total score on the Disability Rating Scale, Glasgow Coma Scale Score and age—which correctly classified 74% of...

Raised intracellular [Ca2+] abolishes excitation‐contraction coupling in skeletal muscle fibres of rat and toad.

Abstract: 1. Raising the intracellular [Ca2+] for 10 s at 23 degrees C abolished depolarization-induced force responses in mechanically skinned muscle fibres of toad and rat (half-maximal effect at 10 and 23 microM, respectively), without affecting the ability of caffeine or low [Mg2+] to open the ryanodine receptor (RyR)/Ca2+ release channels. Thus, excitation-contraction coupling was lost, even though the Ca2+ release channels were still functional. Coupling could not be restored in the duration of an experiment (up to 1 h). 2. The Ca(2+)-dependent uncoupling had a Q10 > 3.5, and was three times slower at pH 5.8 than at pH 7.1. Sr2+ caused similar uncoupling at twenty times higher concentration, but Mg2+, even at 10 mM, was ineffective. Uncoupling was not noticeably affected by removal of ATP or application of protein kinase or phosphatase inhibitors. 3. Confocal laser scanning microscopy showed that the transverse tubular system was sealed in its entirety in mechanically skinned fibres and that its integrity was maintained in uncoupled fibres. Electron microscopy revealed distorted or severed triad junctions and Z-line aberrations in uncoupled fibres. 4. Only when uncoupling was induced at a relatively slow rate (e.g. over 60 s with 2.5 microM Ca2+) could it be prevented by the protease inhibitor leupeptin (1 mM). Immunostaining of Western blots showed no evidence of proteolysis of the RyR, the alpha 1-subunit of dihydropyridine receptor (DHPR) or triadin in uncoupled fibres. 5. Fibres which, whilst intact, were stimulated repeatedly by potassium depolarization with simultaneous application of 30 mM caffeine showed reduced responsiveness after skinning to depolarization but not to caffeine. Rapid release of endogenous Ca2+, or raised [Ca2+] under conditions which minimized the loss of endogenous diffusible myoplasmic molecules from the skinned fibre, caused complete uncoupling. Taken together, these results suggest that Ca(2+)-dependent uncoupling can also occur in intact fibres. 6. This Ca(2+)-dependent loss of depolarization-induced Ca2+ release may play an important feedback role in muscle by stopping Ca2+ release in localized areas where it is excessive and may be responsible for long-lasting muscle fatigue after severe exercise, as well as contributing to muscle weakness in various dystrophies.

Myelin oligodendrocyte glycoprotein induces a demyelinating encephalomyelitis resembling multiple sclerosis.

Abstract: Chronic relapsing experimental autoimmune encephalomyelitis, a demyelinating disease induced by injection of central nervous system (CNS) tissue, is widely used as a model for multiple sclerosis. However, it is unclear which Ag or combination of Ags in the CNS induce the demyelinating immune response. We now show in Lewis rats that a single injection of myelin oligodendrocyte glycoprotein, a specific CNS myelin component, or an appropriately derived myelin oligodendrocyte glycoprotein peptide produces a relapsing remitting neurologic disease with extensive plaque-like demyelination. Igs from affected animals reacted specifically with myelin oligodendrocyte glycoprotein and stimulated a myelin protease activity, leading to myelin basic protein degradation. The demonstrated involvement of myelin oligodendrocyte glycoprotein as a new demyelinating neural Ag may provide a deeper insight into the pathogenesis of multiple sclerosis and its treatment.

The effect of household distribution on transmission and control of highly infectious diseases

Abstract: Two epidemic threshold parameters are derived for the spread of a highly infectious disease in a community of households, where a household is any group whose members have frequent contacts with each other. It is assumed that the infection of any member of a household results in the infection of all susceptible members of that household. The threshold parameters have simple expressions in terms of the mean household size and the mean and variance of the number of susceptibles per household. They provide a basic reproduction number R0 for the spread of infection from individual to individual and a basic reproduction number RH0 for the spread of infection from household to household. The threshold parameters are used to derive the levels of immunity required for the prevention of major epidemics in the community. They are also used to evaluate various vaccination strategies having the same vaccination coverage. For a community with households of equal size, it is found that random vaccination of individuals is better than immunizing all members of a corresponding fraction of households. In contrast, when households have varying sizes, immunizing all members of large households can be better than a corresponding vaccination coverage of randomly selected individuals. It is illustrated that these threshold parameters can also be used for a community of households with schools or day care centers. In particular, the effectiveness of immunizing all members of a school is quantified.

Risk factors for stress fractures in female track-and-field athletes: a retrospective analysis.

Abstract: The incidence and nature of stress fractures and the relationship of potential risk factors to stress-fracture history were investigated retrospectively in a group of 53 female competitive track-and-field athletes. Forty-five stress fractures, diagnosed by clinical findings and bone scan, radiograph, or CT scan, were reported in 22 women. Tibial fractures were the most common (33%). There was no significant difference in bone mineral density at the lumbar spine and tibia/fibula or in percentage body fat and total lean mass when comparing the groups with and without a stress-fracture history. Athletes with a past stress fracture were significantly older at menarche and were more likely to have experienced a history of menstrual disturbance (p < 0.05). Analysis of dietary behavior found that athletes with stress fractures scored significantly higher on the EAT-40 test and were more likely to engage in restrictive eating patterns and dieting. Multiple logistic regression showed that athletes with a history of oligomenorrhea were six times more likely to have sustained a stress fracture in the past, while those who were careful about their weight were eight times more likely. Prevention and treatment of stress fractures in female athletes should include a thorough assessment of menstrual characteristics and dietary patterns.

Electrochemical Study of Microcrystalline Solid Prussian Blue Particles Mechanically Attached to Graphite and Gold Electrodes: Electrochemically Induced Lattice Reconstruction

Abstract: The voltammetric behavior of solid Prussian blue mechanically attached to graphite, glassy carbon, or gold electrodes as an array of microscopically small particles is extremely well defined when the electrode is placed in aqueous media containing suitable electrolytes. Electron microscopy, electron microprobe analysis, and in situ electrochemical quartz crystal microbalance techniques have been used in addition to the voltammetric data, to characterize the redox and ion-transport processes of solids attached to the electrode. The results compare favorably with published studies based on electrogenerated films, although, as expected, the scan rate dependence is different when solid particles are used. Ion-exchange reactions accompanying redox processes have been examined in K+ and Cd2+ containing aqueous electrolyte solutions, and two types of ion exchange can be distinguished. These are based on replacement of interstitial positions and replacement of lattice positions. An overall reaction scheme based on electrochemically initiated lattice reconstruction is presented to explain the generation of cadmium hexacyanoferrate when oxidation or reduction of Prussian blue occurs at the electrode-solid-K+/Cd2+ containing aqueous electrolyte interface.

Characterizing heavy‐metal adsorption on oxides and oxyhydroxides

Abstract: Adsorption of Cu(II), Zn(II), Co(II) and Cd(II) on three different substrates : goethite, alumina and silica, was investigated over the pH range from 3.5 to 10. The consistent variation in the pH at which 50% of the metal is adsorbed (pH 50 ) indicates that the identity of the adsorbing ion is the principal factor determining the pH range over which adsorption occurs. However, the nature of the substrate does play a lesser role. The proton coefficient, χ, ranged from about 0.5 to 1.8, and was correlated with the difference between pH 50 and the pH for 50% precipitation. It is suggested that for most metal-substrate systems, for which χ is about 1, MOH + plays a dominant role in adsorption. Increasing the substrate concentration decreased pH 50 for adsorption of metals on goethite, but there was little change in χ. The change in pH 50 was inversely related to X. While the effect of the nature and concentration of the background electrolyte on Cu(II), Zn(II) and Co(II) adsorption depended on the substrate, increased ionic strength was found to decrease Cd(II) adsorption on all substrates.

A Score Test against One-Sided Alternatives

Abstract: A score-type statistic, T s , is introduced for testing H: ψ = 0 against K: ψ ≥ 0 and more general one-sided hypotheses when nuisance parameters may be present; ψ is a vector parameter. The main advantages of T s , are that it requires estimation of the model only under the null hypothesis and that, it is asymptotically equivalent to the likelihood ratio statistic; these are precisely the reasons for the popularity of the score tests for testing against two-sided alternatives. In this sense, T s preserves the main attractive features of the classical two-sided score test. The theoretical results are presented in a general framework where the likelihood-based score function is replaced by an estimating function so that the test is applicable even if the exact population distribution is unknown. Computation of T s , is simplified by the fact that it can be computed easily once the corresponding two-sided statistic has been computed. The relevance and simplicity of T s are illustrated by discussing ...

The development of patterns of stable, transient, and school-age onset aggressive behavior in young children.

Abstract: Objective To examine the development of patterns of aggressive behavior in children from the age of 2 to 8 years. Method Children with early histories of aggressive behavior were selected from a community sample of 2,400 infants participating in a longitudinal study. The sample was divided into four groups: children with stable aggressive behavior, those with transient aggression, those with aggression only after age 5 years (late onset), and a comparison group of nonaggressive children. Results Children with stable aggressive behavior were characterized by a difficult temperament, hostile sibling interactions, maternal perception of the child as difficult, and harsher child-rearing practices. Children whose early aggression decreased over time and those who became aggressive only after entering school could not be reliably classified with the selected family variables. Teacher ratings of temperament factors of task orientation and reactivity and ability ratings correctly classified 74% of children whose aggression began at school-age. Conclusions Children with persistent aggressive behavior differed from those who improved, predominantly in terms of symptom severity. Problems with aggression can be identified early in development, and a significant proportion of aggressive children are at risk for continuing social and scholastic difficulties. Knowledge of associated factors may play an important role in prevention.

Characterizing trace metal adsorption on kaolinite

Abstract: Summary Adsorption of Cu(II), Zn(II), Co(II) and Cd(II) on kaolinite has been investigated at 25°C as a function of pH, concentration of the substrate, and the nature and concentration of the supporting electrolyte. The adsorption edges for three metals (Zn(II), Co(II) and Cd(II)) showed clear evidence of two distinct adsorption processes. As the pH was increased adsorption began at pH 4.5 for all metals, but the fraction of metal adsorbed at the completion of the first stage differed, the order being Zn(II)>Co(II)∼Cd(II). The second stage of adsorption had characteristics similar to those for adsorption of the metals on alumina and silica. Type 1 adsorption (the first stage) probably occurs on the permanent negatively charged kaolinite faces, while Type 2 (the second stage) is associated with the variable-charge surfaces. Increasing the concentration of supporting electrolyte (KNO3 or NaCl) dramatically reduced the extent of Type 1 adsorption: at 0.1 m no evidence of this process existed. At intermediate concentrations electrolytes containing K+ suppressed Type 1 adsorption more than those containing Na+.

The study of logarithmic image processing model and its application to image enhancement

Abstract: Describes a new implementation of Lee's (1980) image enhancement algorithm. This approach, based on the logarithmic image processing (LIP) model, can simultaneously enhance the overall contrast and the sharpness of an image. A normalized complement transform has been proposed to simplify the analysis and the implementation of the LIP model-based algorithms. This new implementation has been compared with histogram equalization and Lee's original algorithm. >

Mitochondrial DNA variation in Moroccan and Spanish honey bee populations

Abstract: The mitochondrial DNAs of 192 Moroccan and 173 Spanish honey bee colonies were characterized by a rapid test involving the restriction by DraI of a PCR‐fragment of the COI‐COII region. In Morocco, we found eight haplotypes, all characteristic of the African (A) lineage, suggesting that most if not all the maternal lineages of the colonies repeatedly imported from Europe over the last 150 years have not contributed mitochondrial genomes to the local population. Using two new genetic distances analogous to the shared allele distance defined for nuclear genes, we showed that Morocco was most probably colonized by two sublineages, one from the north‐east and the other one from the south of the country and that the contact zone between them extends along both sides of the Atlas range. In Spain, we found eight haplotypes characteristic of lineage A (six in common with Morocco) and four of lineage M (the West European lineage). The distribution of haplotypes of both lineages forms a gradient with c. 10% of lineage M in the south of Spain (Seville) and up to 100% in the north (San Sebastian). Three hypotheses are presented to explain the large differences of haplotype frequencies between Moroccan and lineage A Spanish colonies: a non‐Moroccan origin of lineage A in Spain, an ancient Moroccan origin or a recent Moroccan origin with a rapid shift of haplotype frequencies due to a founder effect.

Sexuality and older people: revisiting the assumptions

Abstract: Anyone who aspires to a fulfilling life would probably accept that this should include a right to sexual fulfillment. Yet modern Western culture continues to deny older people the same opportunities enjoyed by the young to express their sexuality. We review the psychosocial and physiological factors that influence the sexual expression of older people, provide a critical review of research paradigms used in the study of aging and sexuality, and discuss educational issues that health professionals and older people themselves must consider in order to dispel myths about asexual older people. We argue that it should not be assumed that the physical and pathological changes associated with advancing age reduce the opportunity to enjoy sex. Alternative interpretations and expressions of sexuality may be one of the great opportunities of growing older, especially in the absence of societal and culturally adverse expectations and attitudes.

Dose dependent effects of S-20098, a melatonin agonist, on direction of re-entrainment of rat circadian activity rhythms

Abstract: The chronobiotic properties of melatonin are well documented. For example, following an 8-h phase advance of the light-dark cycle daily injections of melatonin administered at the pre-shift dark onset alter the direction of re-entrainment of rat activity rhythms. Using this 8-h phase advance paradigm, the effects of the melatonin agonist S-20098 (1 mg/kg and 3 mg/kg) on the rat circadian system were compared with those of melatonin. S-20098 altered the direction of re-entrainment in the same manner as melatonin. A study using lower doses of S-20098 showed that the effect on direction of re-entrainment was dose-dependent, with 100% of rats responding at a dose of 100 micrograms/kg. S-20098 may, therefore, have therapeutic potential as a chronobiotic in the treatment of circadian disorders in humans.

The evolution of mammalian sex chromosomes and the origin of sex determining genes

Abstract: Mammals have XX female: XY male chromosomal sex determination in which a small heterochromatic Y controls male development. Only a few active genes have been identified on the Y, including the testis determining factor SRY and candidate spermatogenesis genes. These genes, as well as several pseudogenes, have close relatives on the X, confirming that the Y was originally homologous to the X, but has been progressively degraded. We used comparative gene mapping of sex chromosomes from the three major groups of extant mammals (eutherians, marsupials and monotremes) to deduce how the X and Y evolved from a pair of autosomes, and how SRY assumed control of sex determination. We found that part of the X, and a corresponding region of the Y chromosome, is shared by all mammals and must be very ancient, but part of the X (and Y) was added quite recently. I propose that a small original X and Y were enlarged by cycles of autosomal addition to one partner, recombination onto the other and continuing attrition of the compound Y. This addition-attrition hypothesis predicts that the pseudoautosomal region of the human X is merely a relic of the last addition, and that the gene content of the pseudoautosomal region may well differ in different mammalian lineages. The only genes which remained active on the conserved or added regions of the Y were those, like SRY, that evolved functions in male sex determination and differentiation distinct from the general functions of their X-linked partners. Although the vertebrate gonadogenesis pathway is highly conserved, its control circuitry has probably changed radically and rapidly in evolution.