*  Transitions Between Male and Female Heterogamety Caused by Sex-Antagonistic Selection | Genetics
Genetic sex determination in some groups of animals appears to make frequent shifts between male heterogamety (XY) and female heterogamety (ZW) systems (Ezaz et al. 2006). Several mechanisms can cause these transitions, including selection on pleiotropic effects of the sex-determination genes, selection on sex ratio, and meiotic drive. Our results add to this list of possibilities. We find that sexually antagonistic selection on loci linked to the sex-determination genes can trigger a heterogamety transition. Sex-antagonistic selection is thought to be key to the evolution of other aspects of sex chromosomes (Charlesworth 1991), and so it seems plausible that it may commonly be involved in these transitions as well.. The way ...
*  Karyotype and sex chromosome differentiation in two Nalassus species (Coleoptera, Tenebrionidae)
Cytogenetic features of Nalassus bozdagus Nabozhenko & Keskin, 2010 and Nalassus plebejus Küster, 1850 were analysed using conventional and differential staining. Mitotic and meiotic chromosomal analysis revealed the diploid number as 2n = 20 (9+Xyp) in both species. Besides the general resemblance of two Nalassus Mulsant, 1854 karyotypes, important differences related to variations in the number of metacentric/submetacentric chromosomes, localization of highly impregnated regions which are considered as NOR and heterochromatin distribution are clearly observed. The most prominent difference between two species is found related to the X chromosome which is clearly larger in N. bozdagus and has a conspicuous secondary constriction on the long arm. As a result of silver staining, the existence of highly impregnated areas associated with Xyp of N. bozdagus in both prophase I and metaphase I, suggests that NORs are seemingly located on ...
*  Avian sex chromosome dimorphism | Biology Letters
The evolution of sex chromosome dimorphism (SCD) is generally thought to follow a repeatable pattern. If one of the sex chromosomes carries a sex-determining region with at least two loci that should be linked together, selection favours the process of preventing sex chromosomes from recombination [1,2]. In turn, the lack of recombination leads to degeneration of the chromosome that is present only in one sex. The genetic degeneration of the hemizygous chromosome can occur because of Hill-Robertson effects, such as Muller's ratchet, background selection and the hitchhiking of deleterious alleles to advantageous mutations (reviewed in Charlesworth & Charlesworth [3]). Genetic degeneration, accompanied by morphological shrinking of hemizygous ...
*  The influence of sex chromosome aneuploidy on brain asymmetry. - Department of Psychiatry
The cognitive deficits present in individuals with sex chromosome aneuploidies suggest that hemispheric differentiation of function is determined by an X-Y homologous gene [Crow (1993); Lancet 342:594-598]. In particular, females with Turner's syndrome (TS) who have only one X-chromosome exhibit deficits of spatial ability whereas males with Klinefelter's syndrome (KS) who possess a supernumerary X-chromosome are delayed in acquiring words. Since spatial and verbal abilities are generally associated with right and left hemispheric function, such deficits may relate to anomalies of cerebral asymmetry. We therefore applied a novel image analysis technique to investigate the relationship between sex chromosome dosage and structural brain asymmetry. Specifically, we tested Crow's prediction that the magnitude of the brain torque (i.e., a combination of rightward frontal and leftward occipital asymmetry) would, as a function of ...
*  Evolution of sex chromosomes and sex-biased gene expression | Department of Biology
Sex chromosomes have evolved from non-sex-determining chromosomes (autosomes) many times throughout the tree of life. Ever since their discovery, these chromosomes have captivated researchers because of their obvious involvement in fundamental aspects of an organism's life, such as sex determination, sexual reproduction and sexual conflicts. Despite this long-lasting fascination, their biology remains unclear in several central aspects, in particular regarding their almost ubiquitous evolution of recombination cessation and impoverished gene content, and the multifaceted consequences thereof. This lack of detailed knowledge about sex chromosome evolution compromises our ...
*  Karyotypes, sex chromosomes and change of chromosome number - Revision Cards in University Biology
Maleness in humans is caused by the presence of the Y chromosome not by the lack of a second X chromosome. Obvious from studying sex chomosome abnormalities such as Klinefelter syndrome (causes XXY males) and Turner syndrome (causes X females).. Incidence of sex chromosome disorders is high. Caused by nondisjunction at anaphase I and II of meiosis. This causes some of the gametes to be unbalanced as both sex chromosomes will pass to one daughter nucleus.. The Y chromosome actively diverts the undifferentiated gonad in the developing embryo there is evidence of a testis-determining gene. As crossing over commonly occurs in the pseudoautosomal region, it indicates the gene is in the sub-terminal region of Y.. Other genes are present on the sex chromosomes than sex ...
*  The origin of sex chromosomes › News in Science (ABC Science)
Research published in this week's Science reveals that the Y chromosome developed from an X-like ancestor around 300 million years ago.. Of our 46 human chromosomes, 44 form matched pairs. But two - the X and the Y chromosomes - stand apart because they have no perfect match. But it wasn't always like this. Researchers at the Howard Hughes Medical Institute have found that the X and Y chromosomes evolved from a standard identical pair around 300 million years ago - shortly after the divergence of the evolutionary lines leading to mammals and birds.. "The first events that created the sex chromosomes had been thought to have occurred at least 170 million years ago," says researcher Dr David Page. "We're pushing that back another 100 million years or so.". Page and colleague Dr Bruce Lahn reconstructed the stages of ...
*  Sex Chromosomes: Genetics, Abnormalities, and Disorders
Sex chromosomes determine the sex of an organism. A human somatic cell has two sex chromosomes: XY in male and XX in female. A human germ cell has one sex chromosome: X or Y in a sperm and X in an egg. When an X-sperm is combined with an egg, the resulting zygote (fertilized egg) will contain two X chromosomes. A person developed from the XX-zygote will have the characteristics of a female. Combination of a Y-sperm and an egg will produce a male.Usually, a woman has two X chromosomes (XX) and a man one X and one Y (XY). However, both male and female characteristics can sometimes be found in one individual, and it is possible to have XY women and XX men. Analysis of such individuals has revealed some of the molecules involved in ...
*  Journal papers online - reference list - The Classroom @ The Coop
Comparisons of the sex chromosome systems in birds and mammals are widening our view and deepening our understanding of vertebrate sex chromosome organization, function, and evolution. Birds have a very conserved ZW system of sex determination in which males have two copies of a large, gene-rich Z chromosome, and females have a single Z and a female-specific W chromosome. The avian ZW system is quite the reverse of the well-studied mammalian XY chromosome system, and evolved independently from different autosomal blocs. Despite the different gene content of mammal and bird sex chromosomes, there are many parallels. Genes on the bird Z and the mammal X have both undergone selection for male-advantage functions, and there has been amplification of male-advantage genes and accumulation of LINEs. The bird W and mammal Y have both undergone ...
*  Sex Hormones and Sex Chromosomes Cause Sex Differences in the Development of Cardiovascular Diseases | ...
This review summarizes recent evidence concerning hormonal and sex chromosome effects in obesity, atherosclerosis, aneurysms, ischemia/reperfusion injury, and hypertension. Cardiovascular diseases occur and progress differently in the 2 sexes, because biological factors differing between the sexes have sex-specific protective and harmful effects. By comparing the 2 sexes directly, and breaking down sex into its component parts, one can discover sex-biasing protective mechanisms that might be targeted in the clinic. Gonadal hormones, especially estrogens and androgens, have long been found to account for some sex differences in cardiovascular diseases, and molecular mechanisms mediating these effects have recently been elucidated. More ...
*  Using conventional F-statistics to study unconventional sex-chromosome differentiation [PeerJ]
Species with undifferentiated sex chromosomes emerge as key organisms to understand the astonishing diversity of sex-determination systems. Whereas new genomic methods are widening opportunities to study these systems, the difficulty to separately characterize their X and Y homologous chromosomes poses limitations. Here we demonstrate that two simple F-statistics calculated from sex-linked genotypes, namely the genetic distance (Fst) between sexes and the inbreeding coefficient (Fis) in the heterogametic sex, can be used as reliable proxies to compare sex-chromosome differentiation between populations. We correlated these metrics using published microsatellite data from two frog species (Hyla arboreaand Rana temporaria), and show that they ...
According to dominant models of sex chromosome evolution (Ohno 1967; Bull 1983; Rice 1996), the initial step in the life of a sex chromosome is set by an autosomal mutation (or gene duplication) that interacts with the sex-determining cascade, such that heterozygotes develop into one sex (e.g., XY males), while homozygotes develop into the other (XX females).. Sexually antagonistic mutations should soon accrue in the vicinity of this gene, benefiting from linkage disequilibrium with the sex-determining locus (Fisher 1931; Rice 1987). Cosegregation with sex will then be improved through reduced recombination in the heterogametic sex (Nei 1969; Charlesworth and Charlesworth 1980; Bull 1983; Rice 1987). This nonrecombining ...
*  Y Chromosome Differentiation 180 Million Years Old | Men on the Moon
Just published in Nature is a study revealing the origins of maleness in mammals. The team of Prof. Henrik Kaessmann at the Center for Integrative Genomics and the Swiss Institute of Bioinformatics concludes that the key male-differentiating features in the Y chromosome appeared 180 million years ago in placentals and marsupials with the arrival of…
*  Sex-chromosome Synonyms, Sex-chromosome Antonyms | Thesaurus.com
Synonyms for sex-chromosome at Thesaurus.com with free online thesaurus, antonyms, and definitions. Dictionary and Word of the Day.
*  Sex chromosome | genetics | Britannica.com
Sex chromosome: Sex chromosome, either of a pair of chromosomes that determine whether an individual is male or female. The sex chromosomes of human beings and other mammals are designated by scientists as X and Y. In humans the sex chromosomes comprise one pair of the total of 23 pairs of chromosomes. The other
*  Sex Chromosomes | Blausen Medical
Sex chromosomes determine the sex of an individual. Humans have two sex chromosomes: XX for females and XY for males (as shown in this karyotype).
*  ROSALIND | Glossary | Sex chromosome
A sex chromosome is one of a special (nonhomologous) pair of chromosomes found in animals and determining sex and sex-linked traits; female animals possess two X chromosomes, whereas males possess an X chromosome as well as a shortened Y chromosome.. In humans, the X and Y chromosomes form the 23rd pair of chromosomes.. ...
*  You Can Get Pregnant in Your 40's: Sex chromosome gene link to infertility
Sharing articles I find, discussing options you might consider and suggesting what might help. Each person is different, what works for one might really mess up another. So what you do with this info is entirely up to you
*  Allosome - Wikipedia
An allosome (also referred to as a sex chromosome, heterotypical chromosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical pair of mammal allosomes, determine the sex of an individual created in sexual reproduction. Autosomes differ from allosomes because autosomes appear in pairs whose members have the same form but differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another and thereby determine sex. In humans, each cell nucleus contains 23 pairs of chromosomes, a total of 46 chromosomes. The first 22 pairs are ...
*  Sex chromosomes, sex determination, and sex-linked sequences in Microtidae - Abstract - Cytogenetic and Genome Research ...
The Arvicolidae is a widely distributed rodent group with several interesting characteristics in their sex chromosomes. Here, we summarize the actual knowledge of some of these characteristics. This m
*  NewsRoomAmerica.com - Knowledge Gap On The Origin Of Sex
Newsroom America) -- There are significant gaps in our knowledge on the evolution of sex, according to a research review on sex chromosomes from Lund University in Sweden. Even after more than a century of study, researchers do not know enough about the evolution of sex chromosomes to understand how males and females emerge.. Greater focus on ecological aspects would increase this knowledge, according to evolutionary biologists at Lund University, who have reviewed a lot of the research conducted in this field in the last 100 years.. Female and male bodies work differently, even though they have the same genome. One example is reproduction.. "There is a form of genetic conflict between the sexes - a conflict in the genome itself - which we know little about", says professor Bengt Hansson at Lund University.. ...
*  Chromosomes
... are cell structures that carry genetic material (DNA), or genes. They are a part of every cell in the body. Humans have 46 chromosomes (23 pairs). Half of a person's chromosomes come from the mother and half from the father. One of the 23 pairs determines a person's sex. The sex chromosomes are called X and Y. For a child to be female, she must inherit an X chromosome from each parent
*  MedWorm Heart Transplant | Transplant Professional Portal
This study is the first to examine the involvement of sex chromosomes in the disease's development in the absence of sex hormones. In humans, females typically have two copies of the X chromosome, while males typically have one X and one Y chromosome.METHODIn the lab, the researchers engineered mice with different chromosomal makeups and measured their development of pulmonary hypertension in an environment with 10 percent oxygen, which is a well-established setting for inducing the disease.One group of mice was engineered with sex chromosomes that were independent of their gonadal sex, or sex based on their genitalia, so that the researchers could isolate the impact of sex chromosomes. The other group of ...
*  Lec6 illustrations - LECTURE 6 Thursday January 26 Sex determination and sex chromosomes Announcements/reminders/comments...
View Notes - Lec6_illustrations from BICD 100 at UCSD. LECTURE 6 Thursday, January 26 Sex determination and sex chromosomes Announcements/reminders/comments Review from lecture #5 Sex-limited and
*  Male fruit fly karyotype - Stock Image C001/8373 - Science Photo Library
Male fruit fly (Drosophila sp.) karyotype. A karyotype is the complete set of chromosomes of an organism. Fruit flies have 8 chromosomes in total: 4 inherited from the mother and 4 from the father. The sex chromosomes, which determine the individual's gender, are at bottom right. Males have an X sex chromosome and a Y sex chromosome, females have two X sex chromosomes. - Stock Image C001/8373