The human Y chromosome contains very low levels of nucleotide variation. It has been variously hypothesized that this invariance reflects historic reductions in the human male population, a very recent common ancestry, a slow rate of molecular evolution, an inability to evolve adaptively, or frequent selective sweeps acting on genes borne on the Y chromosome. We propose an alternative theory in which human Y chromosome evolution is driven by mutations in the maternally inherited mitochondrial genome, which impair (...) male fertility and ultimately lead to a reduction in the effective population size (Ne) and consequently the variability of the Y chromosome. BioEssays 24:275–279, 2002. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/bies.10062. (shrink)

The Y chromosome in the XY sex-determination system is often shorter than its X counterpart, a condition attributed to degeneration after Y recombination ceases. Contrary to the traditional view of continuous, gradual degeneration, our study reveals stabilization within large mating populations. In these populations, we demonstrate that both mutant and active alleles on the Y chromosome can reach equilibrium through a mutation-selection balance. However, the emergence of a new species, particularly through the founder effect, can disrupt this equilibrium. (...) Specifically, if the male founders of a new species carry only a mutant allele for a particular Y-linked gene, this allele becomes fixed, leading to the loss of the corresponding active gene on the Y chromosome. Our findings suggest that the rate of Y-chromosome degeneration may be linked to the frequency of speciation events associated with single-male founder events. (shrink)

Loss of the Y‐chromosome is a common feature of species with chromosomal sex determination. However, our understanding of why some lineages frequently lose Y‐chromosomes while others do not is limited. The fragile Y hypothesis proposes that in species with chiasmatic meiosis the rate of Y‐chromosome aneuploidy and the size of the recombining region have a negative correlation. The fragile Y hypothesis provides a number of novel insights not possible under traditional models. Specifically, increased rates of Y aneuploidy may (...) impose positive selection for (i) gene movement off the Y; (ii) translocations and fusions which expand the recombining region; and (iii) alternative meiotic segregation mechanisms (achiasmatic or asynaptic). These insights as well as existing evidence for the frequency of Y‐chromosome aneuploidy raise doubt about the prospects for long‐term retention of the human Y‐chromosome despite recent evidence for stable gene content in older non‐recombining regions. (shrink)

Studies of Y chromosome evolution often emphasize gene loss, but this loss has been counterbalanced by addition of new genes. The DAZ genes, which are critical to human spermatogenesis, were acquired by the Y chromosome in the ancestor of Old World monkeys and apes. We and our colleagues recently sequenced the rhesus macaque Y chromosome, and comparison of this sequence to human and chimpanzee enables us to reconstruct much of the evolutionary history of DAZ. We report that (...) DAZ arrived on the Y chromosome about 38 million years ago via the transposition of at least 1.1 megabases of autosomal DNA. This transposition also brought five additional genes to the Y chromosome, but all five genes were subsequently lost through mutation or deletion. As the only surviving gene, DAZ experienced extensive restructuring, including intragenic amplification and gene duplication, and has been the target of positive selection in the chimpanzee lineage.Editor's suggested further reading in BioEssays Should Y stay or should Y go: The evolution of non‐recombining sex chromosomes Abstract. (shrink)

The special properties of the Y chromosome stem form the fact that it is a non‐recombining degenerate derivative of the X chromosome. The absence of homologous recombination between the X and the Y chromosome leads to gradual degeneration of various Y chromosome genes on an evolutionary timescale. The absence of recombination, however, also favors the accumulation of transposable elements on the Y chromosome during its evolution, as seen with both Drosophila and mammalian Y chromosomes. Alongside (...) these processes, the acquisition and amplification of autosomal male benefit genes occur. This review will focus on recent studies that reveal the autosome‐acquired genes on the Y chromosome of both Drosophila and humans. The evolution of the acquired and amplified genes on the Y chromosome is also discussed. Molecular and comparative analyses of Y‐linked repeats in the Drosophila melanogaster genome demonstrate that there was a period of their degeneration followed by a period of their integration into RNAi silencing, which was beneficial for male fertility. Finally, the function of non‐coding RNA produced by amplified Y chromosome genetic elements will be discussed. BioEssays 27:1256–1262, 2005. © 2005 Wiley Periodicals, Inc. (shrink)

The Y chromosomes of most Drosophila species are necessary for male fertility but they are not involved in sex determination. They have many puzzling properties that resemble the effects caused by B chromosomes. Classical genetic and molecular studies reveal substantial affinities between Y and B chromosomes and suggest that the Y chromosomes of Drosophila are not degenerated homologues of the X chromosomes, but rather that their Y chromosomes evolved as specialized supernumeraries similar to classical B chromosomes.

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. (shrink)

Gradual degradation seems inevitable for non‐recombining sex chromosomes. This has been supported by the observation of degenerated non‐recombining sex chromosomes in a variety of species. The human Y chromosome has also degenerated significantly during its evolution, and theories have been advanced that the Y chromosome could disappear within the next ∼5 million years, if the degeneration rate it has experienced continues. However, recent studies suggest that this is unlikely. Conservative evolutionary forces such as strong purifying selection and intrachromosomal (...) repair through gene conversion balance the degeneration tendency of the Y chromosome and maintain its integrity after an initial period of faster degeneration. We discuss the evidence both for and against the extinction of the Y chromosome. We also discuss potential insights gained on the evolution of sex‐determining chromosomes by studying simpler sex‐determining chromosomal regions of unicellular and multicellular microorganisms. (shrink)

PURPOSE:To report the localization of a gene causing drusen and macular degeneration in a previously undescribed North American family. METHODS:Genetic mapping studies were performed using linkage analysis in a single family with drusen and atrophic macular degeneration. RESULTS:The clinical manifestations in this family ranged from fine macular drusen in asymptomatic middle-aged individuals to atrophic macular lesions in two children and two elderly patients. We mapped the gene to chromosome 6q14 between markers D6S2258 and D6S1644. CONCLUSIONS:In a family with autosomal (...) dominant drusen and atrophic macular degeneration, the gene maps to a 3.2-cM region on chromosome 6q14. This locus appears to be distinct from, but adjacent to, the loci for cone-rod dystrophy 7 (CORD7) and North Carolina macular dystrophy (MCDR1). Future identification of the gene responsible for the disease in this family will provide a better understanding of macular degeneration. (shrink)

The spatial organization of the genome is intimately linked to its biological function, yet our understanding of higher order genomic structure is coarse, fragmented and incomplete. In the nucleus of eukaryotic cells, interphase chromosomes occupy distinct.

Nucleotide diversity of the human Y chromosome is much lower than that in the rest of the genome. A new hypothesis postulates that this invariance may result from mutations in maternally inherited mitochondrial DNA (mtDNA), leading to impaired reproduction among males and lowered male effective population size. If correct, we should expect to see low levels of polymorphism in the male‐specific Y chromosome of many organisms but not necessarily in the female‐specific W chromosome in organisms with female (...) heterogamety. However, recent observations from birds suggest that the avian W chromosome is very low in nucleotide diversity. This indicates that mtDNA mutations cannot broadly explain the evolution of the sex‐limited chromosome. Other work has suggested that sexual selection at loci involved in sex determination or secondary sexual characteristics might reduce levels of genetic variability on Y through hitch‐hiking effects. Although the W chromosome does not seen to play a dominant role for sex determination in birds, it cannot be excluded that selective sweeps arising from natural or sexual selection contribute to the low levels of genetic variability seen on this chromosome. BioEssays 25:163–167, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

Mammalian sex chromosomes exhibit marked sexual dimorphism in behavior during gametogenesis. During oogenesis, the X chromosomes pair and participate in unrestricted recombination; both are transcriptionally active. However, during spermatogenesis the X and Y chromosomes experience spatial restriction of pairing and recombination, are transcriptionally inactive, and form a chromatin domain that is markedly different from that of the autosomes. Thus the male germ cell has to contend with the potential loss of X‐encoded gene products, and it appears that coping strategies have (...) evolved. Genetic control of sex‐chromosome inactivation during spermatogenesis does not involve pairing or the presence of the Y chromosome or an intact X chromosome, and may therefore be under exogenous control by the gonad. Sex‐chromosome reactivation during oogenesis and inactivation during spermatogenesis probably reflect specific meiotic events such as recombination. Understanding these phenomena may help explain other sex‐related differences in genetic recombination. (shrink)

Mammal sex determination depends on an XY chromosome system, a gene for testis development and a means of activating the X chromosome. The duckbill platypus challenges these dogmas.1,2 Gutzner et al.1 find no recognizable SRY sequence and question whether the mammalian X was even the original sex chromosome in the platypus. Instead they suggest that the original platypus sex chromosomes were derived from the ZW chromosome system of birds and reptiles. Unraveling the puzzles of sex determination (...) and dosage compensation in the platypus has been complicated by the fact that it has a surplus of sex chromosomes. Rather than a single X and Y chromosome, the male platypus has five Xs and five Ys. BioEssays 27:681–684, 2005. © 2005 Wiley Periodicals, Inc. (shrink)

Comparative mapping and sequencing show that turnover of sex determining genes and chromosomes, and sex chromosome rearrangements, accompany speciation in many vertebrates. Here I review the evidence and propose that the evolution of therian mammals was precipitated by evolution of the male‐determining SRY gene, defining a novel XY sex chromosome pair, and interposing a reproductive barrier with the ancestral population of synapsid reptiles 190 million years ago (MYA). Divergence was reinforced by multiple translocations in monotreme sex chromosomes, the (...) first of which supplied a novel sex determining gene. A sex chromosome‐autosome fusion may have separated eutherians (placental mammals) from marsupials 160 MYA. Another burst of sex chromosome change and speciation is occurring in rodents, precipitated by the degradation of the Y. And although primates have a more stable Y chromosome, it may be just a matter of time before the same fate overtakes our own lineage. (shrink)

The creeping vole Microtus oregoni exhibits remarkably transformed sex chromosome biology, with complete chromosome drive/drag, X‐Y fusions, sex reversed X complements, biased X inactivation, and X chromosome degradation. Beginning with a selfish X chromosome, I propose a series of adaptations leading to this system, each compensating for deleterious consequences of the preceding adaptation: (1) YY embryonic inviability favored evolution of a selfish feminizing X chromosome; (2) the consequent Y chromosome transmission disadvantage favored X‐Y fusion (...) (“XP”); (3) Xist‐based silencing of Y‐derived XP genes favored a second X‐Y fusion (“XM”); (4) X chromosome dosage‐related costs in XPXM males favored the evolution of XM loss during spermatogenesis; (5) X chromosomal dosage‐related costs in XM0 females favored the evolution of XM drive during oogenesis; and (6) degradation of the non‐recombining XP favored the evolution of biased X chromosome inactivation. I discuss recurrent rodent sex chromosome transformation, and selfish genes as a constructive force in evolution. (shrink)

Chromosomes that harbor dominant sex determination loci are predicted to erode over time—losing genes, accumulating transposable elements, degenerating into a functional wasteland and ultimately becoming extinct. The Drosophila melanogaster Y chromosome is fairly far along this path to oblivion. The few genes on largely heterochromatic Y chromosome are required for spermatocyte‐specific functions, but have no role in other tissues. Surprisingly, a recent paper shows that divergent Y chromosomes can substantially influence gene expression throughout the D. melanogaster genome.1 These (...) results show that variation on Y has an important influence on the deployment of the genome. BioEssays 30:409–411, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

Graphical AbstractOn the Black Swans of conventional sex determination theory: There aren't many, but when an exception to the standard model of sex determination (evolutionary turnover of genes playing the role of “master sex determiner”) arises, it certainly screams out for an explanation. In this issue, a novel one is put forward. It now awaits testing, particularly at the population level.

In most discussions of the evolution of sex chromosomes, it is presumed that the morphological differences between the X and Y were initiated by genetic changes. An alternative possibility is that, in the early stages, a key role was played by epigenetic modifications of chromatin structure that did not depend directly on genetic changes. Such modifications could have resulted from spontaneous epimutations at a sex‐determining locus or, in mammals, from selection in females for the epigenetic silencing of imprinted regions of (...) the paternally derived sex chromosome. Other features of mammalian sex chromosomes that are easier to explain if the epigenetic dimension of chromosome evolution is considered include the relatively large number of X‐linked genes associated with human brain development, and the overrepresentation of spermatogenesis genes on the X. Both may be evolutionary consequences of dosage compensation through X‐inactivation. BioEssays 26:1327–1332, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

Male superiority in mathematical ability (along with female superiority in verbal fluency) may reflect the operation of an X-Y homologous gene (the right-shift-factor) influencing the relative rates of development of the cerebral hemispheres. Alleles at the locus on the Y chromosome will be selected at a later mean age than alleles on the X, and only by females.

Sex chromosomes in plants have been known for a century, but only recently have we begun to understand the mechanisms behind sex determination in dioecious plants. Here, we discuss evolution of sex determination, focusing on Silene latifolia, where evolution of separate sexes is consistent with the classic “two mutations” model—a loss of function male sterility mutation and a gain of function gynoecium suppression mutation, which turned an ancestral hermaphroditic population into separate males and females. Interestingly, the gynoecium suppression function in (...) S. latifolia evolved via loss of function in at least two sex‐linked genes and works via gene dosage balance between sex‐linked, and autosomal genes. This system resembles X/A‐ratio‐based sex determination systems in Drosophila and Rumex, and could represent a steppingstone in the evolution of X/A‐ratio‐based sex determination from an active Y system. (shrink)

Graphical AbstractThe SRY gene, which is located on the Y chromosome and directs male development, may promote aggression and other traditionally male behavioural traits, resulting in the fight-or-flight reaction to stress.

In mammals, the Y chromosome induces testis formation and thus male sexual development; in the absence of a Y chromosome, gonads differentiate into ovaries and female development ensues. Molecular genetic studies have identified the Y‐located testis determining gene SRY as well as autosomal and X‐linked genes necessary for gonadal development. The phenotypes resulting from mutation of these genes, together with their patterns of expression, provide the basis for establishing a hierachy of genes and their interactions in the mammalian (...) sex determination pathway. (shrink)

This commentary examines the use of Y-chromosome testing to reconstruct a genetic ancestry for the Lemba, a group in southern Africa.

Some of my best friends are women, but I would not want my sister to marry one of them. Modern-minded persons criticize me for manifesting such out-dated prejudices, and would like to send me to Coventry for a compulsory course of reindoctrination. They may be right. It could conceivably be the case that in due course the Sex Discrimination Act will be tightened up, even to the extent of our recognizing that there are no ‘good reasons why the State should (...) not recognize contracts which are in all respects like marriage, except for the sex of the parties concerned’. We can envisage a society so enlightened that the relations between men and women will be purely platonic and it will be a matter of no concern whether two people are members of the opposite sex or not: or, alternatively, our feelings could be so completely homogenized, that it will make no difference to an emotional relationship whether Leslie and Julian have only one Y-chromosome between them, or two, or none at all. In that event I shall be shown to be wrong, and my critics entitled to erect a monument to female equality on my grave. But I have doubts, and suspect that long after I am dead men will go on falling in love with women and women will continue to find their hearts wooed and won by men. And this fact, if it is a fact, makes a profound difference to our social institutions. I want to follow out the logic of social differentiation, relying as little as I can on putative facts about the differences between the sexes. Scientifically attested knowledge is scarce in this field. Many academics take refuge in a safe suspension of judgment, but this is a craven dereliction of duty. We have yet to develop an adequate theory of knowledge in social matters, and only by thrashing out the apparently telling arguments on this and similar issues can we clear our minds about the nature of social knowledge. Moreover, if those who might argue rationally draw back from doing so, they leave the field clear for others who suffer from fewer inhibitions and fewer scruples. And finally, serious social consequences can follow from public confusion about the logic of a situation, and what things are possible and what desirable. There is a danger that in our attempts to remedy the real wrongs done to women we shall only succeed, as with much modern legislation, in making a bad case worse. (shrink)

This is the first volume to address directly the question of the speciation of modern Homo sapiens. The subject raises profound questions about the nature of the species, our defining characteristic, and the brain changes and their genetic basis that make us distinct. The British Academy and the Academy of Medical Sciences have brought together experts from palaeontology, archaeology, linguistics, psychology, genetics and evolutionary theory to present evidence and theories at the cutting edge of our understanding of these issues.Palaeontological and (...) genetic work suggests that the transition from a precursor hominid species to modern man took place between 100,000 and 150,000 years ago. Some contributors discuss what is most characteristic of the species, focussing on language and its possible basis in brain lateralization. This work is placed in the context of speciation theory, which has remained a subject of considerable debate since the evolutionary synthesis of Mendelian genetics and Darwinian theory. The timing of specific transitions in hominid evolution is discussed, as also is the question of the neural basis of language. Other contributors address the possible genetic nature of the transition, with reference to changes on the X and Y chromosomes that may account for sex differences in lateralization and verbal ability. These differences are discussed in terms of the theory of sexual selection, and with reference to the mechanisms of speciation.These essays will be vital reading for anyone interested in the nature and origins of the species, and specifically human abilities. (shrink)

ABSTRACTThis commentary examines the relationship between genetics and Jewish identity. It focuses especially on the use of Y‐chromosome testing to map the genealogies of the Lemba in southern Africa.

The genetic stability of living cells is continuously threatened by the presence of endogenous reactive oxygen species and other genotoxic molecules. Of particular threat are the thousands of DNA single-strand breaks that arise in each cell, each day, both directly from disintegration of damaged sugars and indirectly from the excision repair of damaged bases. If un-repaired, single-strand breaks can be converted into double-strand breaks during DNA replication, potentially resulting in chromosomal rearrangement and genetic deletion. Consequently, cells have adopted multiple pathways (...) to ensure the rapid and efficient removal of single-strand breaks. A general feature of these pathways appears to be the extensive employment of protein–protein interactions to stimulate both the individual component steps and the overall repair reaction. Our current understanding of DNA single-strand break repair is discussed, and testable models for the architectural coordination of this important process are presented. BioEssays 23:447–455, 2001. © 2001 John Wiley & Sons, Inc. (shrink)

This article traces the ubiquitous geopolitical metaphors used by researchers in the field of pregnancy-related microchimerism. In this research domain, immunologists and medical geneticists locate ‘non-self’ cells in women by marking Y chromosomes in cells derived from their sons. In the course of this research trajectory, experiments have yielded a number of surprises, beginning with the very presence of these cells in women decades after pregnancy. This finding confounded the expectations predicted by classical immunology, which posits the destruction of such (...) ‘foreign’ entities. Once they were known to be present, fetal cells were implicated in pathological and destructive activity. In a series of reorientations in which metaphor, theory and practice are entangled with matter, the characterization of these cells has shifted from invaders to insurgent foreigners to assimilated productive immigrants. The article reflects on this rich domain of material-semiotic practice to demonstrate that the case of fetomaternal cell trafficking contributes to a growing uneasiness with dominant ontologies of bodies as bounded, defended, pure collectives of homogeneous inhabitants. (shrink)

How is the embryonic bipotential gonad regulated to produce either an ovary or a testis? In males, transient early activation of the Y chromosome Sry gene makes both germ cells and soma male. However, in females, available evidence suggests that the process of ovary sex determination may take place independently in the germline and somatic lineages. In addition, in contrast to testis, in ovary somatic cells, female‐to‐male gonadal sex reversal can occur at times throughout ovary development and maturation. We (...) suggest that a single gene pathway, likely hinging on the Foxl2 transcription factor, both initiates and maintains sex differentiation in somatic cells of the mammalian ovary. BioEssays 29: 15–25, 2007. Published 2006 Wiley Periodicals, Inc. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:XY/XOLianne SimonAs a boy child I might once have thrived, but the loss of a Y chromosome in one of the first few cell divisions left me a faie half–girl struggling for life—like some changeling left in place of a human baby. My genetic mosaic of XY and XO cell lines created a fetal legacy of Turner Syndrome medical issues. Among these were delayed growth, a largely absent (...) puberty, and micrognathia—a small jaw that feminized my face. [End Page E11]At two I weighed just eighteen pounds. My parents worried they might lose their little boy, I was that frail. All I knew was I was the smallest of my peer group and had a cute pixie face. I imagined myself a high–spirited elfin princess, but was in truth shy—almost timid—and prone to tears.I first responded to the Gospel at vacation Bible school. One of the women there read me Bible stories. I didn’t understand them all, but I wanted to love Jesus and be a good girl.At nine I was the size of a 6–year–old. By then I’d started growing faster, so my mother stopped taking me to the doctors. I didn’t see one again until an emergency appendectomy in college.Fifth grade brought surprises. Jim melted my heart with his Beatles love songs and cute smile. I dreamed of being his bride. Karen was the first classmate ever shorter than me. We were best friends, but one day the principal said I should play softball with the boys instead of hopscotch with her.My parents allowed me dolls and tea sets, even an Easy–Bake oven. But wearing my sister’s clothes triggered a sad–eyed lecture—boys didn’t do such things. No dresses. No talking with my hands. No long hair. And no crushes on boys.If I prayed hard enough, if I was really good, maybe God would make me a real boy—tall and strong, fast and agile—like my older brother. Two years later, puberty cracked my high–pitched squeal of a voice and sent it sliding down to a mellower soprano. I grew taller, but didn’t get muscles or body hair, and I remained hopelessly uncoordinated. An inguinal hernia kept me from running very far.High school turned my prayers into pleas for mercy. I despaired of ever fitting in. Some Christians might not have welcomed a feminine boy, but the pastor of our Southern Baptist mission considered me one more sinner in need of the saving grace of a forgiving God. He led me to faith in Christ. As a new believer, I assumed I could be a boy for real. Maybe even find a girlfriend. Instead, the mask that allowed me to function socially crumbled, leaving me no place to hide.In the spring of 1970, I registered for the draft. Me fighting in Vietnam seemed a real possibility. Or at least spending time in prison for refusing induction. Except that a delicate intersex kid would never have passed the physical. Nearly perfect SAT scores won me a scholarship to Miami, so I left a supportive home in Illinois for a boys’ dorm in south Florida.My surname then was Klett. The worst of the guys called me Clit, or sometimes Clitoris. Others derided my small size and lack of virility. One propositioned me. Another used to pin me to my bed and lie on top of me until I quit struggling. Though he stopped each time I surrendered, my defenses lay in ruin.A few of the boys were nice. David took me for long rides on his motorcycle, with my arms wrapped tight around his waist. He treated me with gentle kindness and asked nothing in return.To escape the dorm, I studied in the library stacks, where only honors and graduate students were allowed. The next year I found a derelict building where the university stored old theatrical sets. It even had a quiet place to sit in the sun. Best of all—nobody ever went there.One day my imagination wandered through the wardrobe. What would I have worn... (shrink)

For nearly two centuries, developmental biologists have known that body organs are derived from distinct germ layers. They have argued that adult stem cells formed in one of these, mesoderm for example, cannot give rise to cells that originate in another. We disagree. An exception to this “rule” has been described in crayfish recently. In this species, hemocytes appear to replenish neurogenic cells. This may happen in humans as well. In women who were given male bone marrow‐derived cells, Y (...) class='Hi'>chromosome positive cheek cells and brain neurons were detected. While repopulation of these tissues by bone marrow derived cells may not occur normally, and while it does not appear to be terribly efficient, the phenomenon should be studied in more detail. Perhaps cells in the marrow could be used to regenerate tissues elsewhere. (shrink)

Both religion and science provide powerful images of human origins and human nature. Often these images are seen as incompatible or irreconcilable, with the religious image generally marginalized vis-à-vis the scientific image. Recent genetic studies into human origins, especially in terms of common cellular features like the mitochondrion from females and the Y-chromosome from males, provide evidence for common ancestors called mitochondrial Eve and Y-chromosomal Adam. The aim of this paper is to expound upon the Judeo-Christian and western scientific (...) images of humanity with respect to human origins and human nature, especially in terms of possible reconciliation of the two images. (shrink)

There is an emerging consensus within Natural Law that explains transgender identity as an “embodied misunderstanding.” The basic line of argument is that our sexual identity as male or female refers to our possible reproductive roles of begetting or conceiving. Since these two possibilities are determined early on by the presence or absence of a Y chromosome, our sexual identity cannot be changed or reassigned. I develop an argument from analogy, comparing gender and language, to show that this consensus (...) is premature. Language and gender imbue our body with further social meaning and so, I conclude, that just as we can learn multiple languages, so too can we learn multiple genders. Since language and gender each constitutively contribute to our wellbeing as a “second nature,” I argue against this consensus to show that the reason people who are transgender struggle to flourish is not because of a “troubled trans psyche,” but because there are conceptual, interpersonal, and institutional obstacles stacked against them. (shrink)

Following the tradition of feminist philosophers and scholars of science from the 1980s onward such as Evelyn Fox-Keller, Helen Longino, Anne Fausto-Sterling, and others who revealed how popular notions of masculinity and femininity infiltrated and shaped the content of scientific knowledge, Sarah S. Richardson's book Sex Itself: The Search for Male and Female in the Human Genome deserves a place on the shelf with this canonical literature. It addresses one of the most celebrated symbols of biological sex binary: the X (...) and Y chromosomes. The X and Y chromosomes, we learn, were not given the role of "sex chromosomes" upon their discovery in 1890 and 1905, respectively. Their transformation into the ultimate... (shrink)

ABSTRACT This summary lays out the basic science and methodology used in genetic testing that investigates historical population migrations and the ancestry of living individuals. The genetic markers used in this testing, and the distinction between Y‐chromosome, mitochrondial and autosomes analysis, are explained and the shortcomings of these methodologies are explored.

The endangered species Tokudaia osimensis has the unique chromosome constitution of 2n = 25, with an XO/XO sex chromosome configuration (2n = 25; XO). There is urgency to preserve this species and to elucidate the regulator(s) that can discriminate the males and females arising from the indistinguishable sex chromosome constitution. However, it is not realistic to examine this rare animal species by sacrificing individuals. Recently, true naïve induced pluripotent stem cells were successfully generated from a female T. (...) osimensis, and the sexual plasticity of its germ cells was elucidated. This achievement constitutes the basis of an attractive research area, including embryonic fate determination, sex determination, and factor(s) that can replace the Y chromosome. In this essay, concrete strategies to conserve rare animal species and to reveal their specific characteristics using other compatible and abundant animals are proposed. -/- . (shrink)

Spermatogenesis is an elaborate process involving both cell division and differentiation, and cell‐cell interactions. Defects in any of these processes can result in infertility, and in some cases these can be genetic in cause. Mapping experiments have defined at least three regions of the human Y chromosome that are required for normal spermatogenesis. Two of these contain the genes encoding the RNA binding proteins RBM and DAZ, suggesting that the control of RNA metabolism is likely to be an important (...) control point for human spermatogenesis. A similar analysis in mice has shown that at least two regions of the mouse Y chromosome are essential for spermatogenesis. Both genetic and reverse genetic approaches have been used to identify mouse autosomal genes required for spermatogenesis. These studies have shown that genes in a number of different pathways are essential for normal spermatogenesis, and also provide putative models of human infertility. (shrink)

In recent years, preimplantation genetic testing (PGT) of IVF embryos have gained much traction in clinical assisted reproduction for preventing various genetic defects, including Down syndrome. However, such genetic tests inevitably reveal the sex of IVF embryos by identifying the sex (X and Y) chromosomes. In many countries with less stringent IVF regulations, information on the sex of embryos that are tested to be genetically normal is readily shared with patients. This would thus present Muslim patients with unintended opportunities for (...) sex selection based on personal or social biases without any pressing need or valid medical reason. Additionally, there are other patients who claim using PGT for preventing genetic defects as a pretext or “convenient excuse,” with a secret intention to do sex selection when it is banned in their home country. Currently, non-medical sex selection is a highly-controversial and hotly debated issue in Islam, because there is generally a strong preference for having sons over daughters due to widespread cultural norms of elderly parents depending on their sons for financial support, as well as the need for male heirs to continue the family lineage within the backdrop of local patriarchal cultures. There is a risk of gender imbalance and social disequilibrium occurring in Islamic societies due to prevalent sex selection. Hence, the question is whether opportunistic sex selection with PGT would contravene Islamic ethics and principles, which will thus be discussed here. (shrink)

Different patterns of mitochondrial and Y-chromosome diversity have been cited as evidence of long-term patrilocality in human populations. However, what patterns are expected depends on the nature of the sampling scheme. Samples from a local region reveal only the recent demographic history of that region, whereas sampling over larger geographic scales accesses older demographic processes. A historical change in migration becomes evident first at local geographic scales, and alters global patterns of genetic diversity only after sufficient time has passed. (...) Analysis of forager populations in the ethnographic record suggests that patrilocality may not have predominated among pre-agricultural humans. The higher female migration rate inferred by some genetic studies may reflect a shift to patrilocality in association with the emergence of agriculture. A recent global survey does not show the expected effects of higher female migration, possibly because the sampling scheme used for this study is accessing pre-agricultural human migration patterns. In this paper, we show how the demographic shift associated with agriculture might affect genetic diversity over different spatial scales. We also consider the prospects for studying sex-biased migration using the X-linked and autosomal markers. These multi-locus comparisons have the potential of providing more robust estimates of sex differences than Y-linked and mitochondrial data, but only if a very large number of loci are included in the analysis. BioEssays 28: 290–300, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

Ramathal et al. have employed an elegant xenotransplantation technique to study the fate of human induced pluripotent stem cells (hiPSCs) from fertile males and from males carrying Y chromosome deletions of the azoospermia factor (AZF) region. When placed in a mouse testis niche, hiPSCs from fertile males differentiate into germ cell‐like cells (GCLCs). Highlighting the crucial role of cell autonomous factors in male sterility, hiPSCs derived from azoospermic males prove to be less successful under similar circumstances. Their studies argue (...) that the agametic “Sertoli cell only” phenotype of two of the AZF deletions likely arises from a defect in the maintenance of germline stem cells (GSCs) rather than from a defect in their specification. These observations underscore the importance of the dialogue between the somatic niche and its inhabitant stem cells, and open up interesting questions concerning the functioning of the somatic niche and how it communicates to the GSCs. (shrink)

In recent years, mtDNA and Y chromosome studies involving human populations from South Asia and the rest of the world have revealed new insights about the peopling of the world by anatomically modern humans during the late Pleistocene, some 40,000–60,000 years ago, over the southern coastal route from Africa. Molecular studies and archaeological record are both largely consistent with autochthonous differentiation of the genetic structure of the caste and tribal populations in South Asia. High level of endogamy created by (...) numerous social boundaries within and between castes and tribes, along with the influence of several evolutionary forces such as genetic drift, fragmentation and long‐term isolation, has kept the Indian populations diverse and distant from each other as well as from other continental populations. This review attempts to summarize recent genetic studies on Indian caste and tribal populations with the focus on the information embedded in the socially defined structure of Indian populations. BioEssays 29: 91–100, 2007. © 2006 Wiley Periodicals, Inc. (shrink)