Why is a sex-linked trait rarely (if ever) seen in the opposite sex from the expected sex type?
485911
because if its y linked then women can't have it because women don't have a Y chromosome while if its X linked it is usually recessive so males don't have a dominate allele to counteract it so the recessive shows through and to have two X recessive alleles in one cell is very rare because the male has to have the recessive phenotype and the female has to have a heterozygous genotype. Sorry for the in depth language.
1004595
i didnt know that. i used to think its more common in women because of pregnancy induced glucose intolerance etc,\n\nbut if it is  shown by statistics that its more common in men i think  its related to lifestyle (food , exercise, weight,stress,alcohol etc)\nmeaning that sex is not an independent risk factor for diabetes (at least thats what i think)\n\nthe next posting is talking about   (x linked recessive inheritance) and its got nothing to do with diabetes , you can be sure of that. other diseases like haemophilia are inherited this way .
416191
They are two VERY different creatures and the genetic research they are doing has recently shown that the X chromosome in men and the X chormosome in women is very differnt much to their surprise!\n\nIt is almost like we are two different species genetically.
617160
Chromosomal abnormalities, and missing or extra chromosomes.\n\nAlso sex: there are some XY people who appear to be female.
386547
There are certain genetic characteristics related to each race. This just happens to be a dominant trait with black women, but of course there are exceptions. Every race has a variety of body types
1075172
Although your questions deals more with race than with sexuality, a brief observation is in order: heterosexual intercourse being exclusively the ordinary route to natural human procreation, lifelong homosexuality is understandably rare among persons.\n\nPerhaps as a consequence of this, most cultures seem to have adopted a 2-person form for romantic relationships -- and in some instances, homosexual relationships are sanctioned by the State.\n\nHaving so stated, and in answer to the particulars of your question, this is what I recall from my college studies:\n\nThe following sociological stereotypes were derived by scientists from years of observation, and apply only when the entire earth population of each group is considered: caucasoid males and negroid females tend to be assertive, caucasoid females and negroid males tend to be submissive.\n\nBecause race is a function of evolution, were it not for advances in travel, there would be virtually no interracial couples.  The ancient aphorism is "birds of a feather flock together."\n\nAssertive persons tend to affiliate themselves with others on the basis of ideological compatibility; submissive persons tend to affiliate themselves with others on aesthetic grounds.\n\nNote: ideological compatibility does not preclude selfish motives; in fact, hope to realize one or more selfish aims may be for each party in a couple a driving influence (or even the sole influence).\n\nBeauty is subjective, but within cultural groups exist parameters common to the definition of a standard.  When this observation is applied on a global basis, caucasian women are generally more attractive than negroid women.\n\nThat doesn't mean there aren't stunning "Nubian" women, anymore than it means that there aren't any buggly "white" women.  Rather, it simply acknowledges a general trend that is always going to be locally rebuttable.\n\nOrdinarily, opposites attract (think of the poles of a magnet): assertive men desire as domestic companions submissive women, and vice-versa; however, the value of the aesthetic cannot be simply dismissed.\n\nAesthetic appeal is not limited to the beauty of physical form -- shape, color, tone, vocalization, etc. -- but includes personality.\n\nWith the exacerbation of competitive demands throughout both the global economy and local economies, psychoemotional pressures will continue to increase against effective assertive personalities -- (thus making them increasingly likely to be jerks).\n\nBy contrast, submissive personalities tend either to regard fate as cyclical or inevitable, and cope with the demands of life in a much more carefree manner.  This can't be lost on the "white women" that seem to crave "black men," and vice-versa.
1016963
I have the same problem. My understanding of genetics does not support a "gay gene"; however it is very possible and more frequent then most people think that certain males are exposed to more female hormones than normal and vice versa for females. These hormones (similar to how animals are attracted to one another) can influence whether or not and individual is attracted to males or females. Also (using males as an example) if a boy was exposed to or born with more female hormones and thus acts more feminine, he will most likely be attracted to someone who is opposite to him (hence masculine). It is more natural for feminine and masculine to attract rather than simply male or female. For example I am naturally more attratced to masculine guys, rather than feminine guys. I am not attracted to masculine women ("dykes") simply because society has taught me not to be attracted to women from birth, so my sexual preference is trained towards males...
169848
"The term "hermaphrodite" has historically been used to describe people with ambiguous genitalia or biological sex. The broader term intersexual is often used and is preferred by many such individuals and medical professionals. The term is still used by the pornography industry, though often as a synonym for transsexual, as true human intersexuals are rare."\n\nIntrasexuality is not necessarily chimerism and chimerism is not necessarily intarsexuality or hermaphroditism\n\n"Tetragametic chimerism is a less common cause of congenital chimerism. It occurs through the fertilization of two ova by two spermatozoa, followed by the fusion of the zygotes and the development of an organism with intermingled cell lines. This happens at a very early stage of development, such as that of the blastocyst. Such an organism is called a tetragametic chimera as it is formed from four gametes — two eggs and two sperm.\n\nAs the organism develops, the resulting chimera can come to possess organs that have different sets of chromosomes. For example, the chimera may have a liver composed of cells with one set of chromosomes and have a kidney composed of cells with a second set of chromosomes. This has occurred in humans, though it is considered extremely rare."\n\n"Affected persons are identified by the finding of two populations of red cells or ambiguous genitalia and hermaphroditism alone or in combination; such persons sometimes also have patchy skin or eye pigmentation. If the blastocysts are of the same sex, it can only be detected through DNA testing, which itself is currently rare, and it may be more common than currently believed. If the blastocysts are of opposite sex, genitals of both sexes are formed, either ovary and testis, or combined ovotestes, in one rare form of intersexuality, a condition previously known as true hermaphroditism. As of 2003, there were about 40 human cases in the literature, according to New Scientist.\n\n\n\n\nAccording to the New England Journal of Medicine, vol 338, p 166, physicians in the Western General Hospital of Edinburgh have reported on a child with a penis, one testicle, and an ovary and fallopian tube instead of a second testicle. Some of this child's body cells are XY (male), and some are XX (female). The child was conceived as the result of in-vitro fertilization, and it appears most likely that two embryos, a male embryo and a female embryo, fused before or soon after embryos were transferred to the mother's uterus.\n\nThis kind of condition, where there is more than one set of cell lines with different sets of chromosomes making up the body is known as chimerism. This kind of tetraploid chimerism can also occur naturally, without in-vitro fertilization (see New England Journal of Medicine, vol 346, p 1545).\n\nNot all cases of Chimerism involve intersexuality, however. There have been about 40 known cases worldwide of humans reproducing naturally and producing offspring with absolutely no genetic similarities between mother and child. Discovery Health Channel has produced a documentary on two families and their issues in dealing with chimerism. It was called "I Am My Own Twin.""
769949
well it could either that shes carrying the red/green colorblind trait recessive (sex linked) or not since probability does not guarantee one or the other.
942552
both parents.  Generally, the sex-linked recessive genes are on the X chromosome.  She would have two recessive genes, meaning she had to get a recessive gene from each parent in order to have that phenotype.  The above information is incorrect- sex-linked recessive disorders actually occur more often in men than women because men don't have another X chromosome to nullify the recessive gene.
786358
When Mendal observed that his 7 traits assorted independantly of each other in peas, he assumed that all traits assorted independantly of all other traits, and made that a law of inheritance.\n\nWell, we know know that's wrong.  We observe that while many pairs of traits assort independantly, many other pairs do not.  Thomas Hunt Morgan's lab first observed that fuit fly eye color was linked to fly sex.  Other people observed that other pairs of traits were not totally completely linked, but that they were not totally independant either.  When two traits were found to not assort completely independantly, the term used to describe that situation was "linkage".\n\nWe now know that linkage happens because genes aren't floating around as perfect little gene spheres, bobbing around the nucleus.  They are arranged "like pearls on a string" on chromosomes.  So genes that are on the same string will not assort independently.  Meiosis will sometimes split them, sometimes not, depending on how close the genes are to each other.  They are physically linked, and we call the dependant assortment linkage too.
32401
Biological evolution has nothing to do with it.  Social evolution might.\nHumans seem to be the only species that has some members which are exclusively same sex orientated.  Once classified as a disease, now the causation is unknown.  Conscious choice may have little to do with sexual behavior, and how the programming of the unconscious mind happens is not clearly understood.\nIf the environment has anything to do with this, then it is probably related to population density.\nNo-one knows for sure.  Almost everyone has some pet theory that they want to push as scientific fact.
621951
all normal males are XY.  all normal females are XX.  the female always donates 1 X chromosome to the offspring.  the male donates either an X or a Y to the offspring (50% chance of each event).  If the male donates an X, the offspring will be XX and female.  if the male donates a Y, the offspring will be XY and male.
902693
The answer is an unequivocal "NO"!  For starters, lets look at the rationale against such a proposition.  \n\nEvolutionarily speaking, sexual reproduction is important in that it has the advantage over asexual reproduction of mixing genetic combinations available to the offspring.  In the human species, this sexual reproduction requires both a male and a female.  What accompanies these facts is that the female is genetically prepared to carry a child once pregnant.  Such features which are vital to this are a uterus, the hormones estrogen and progesterone which prepare the uterus for implantation, ovaries to supply eggs, and a vaginal canal for birthing.  All of these features are primary sex characteristics that can only develop in the ABSENCE of a "Y" chromosome.  Evolutionarily, then, it is to the advantage of the species that phenotypic distinctions between males and females exist, and these physical differences preclude the possibility of the male of the species to be capable of pregnancy.  On this logic alone, men can not become pregnant.  But there is more evidence.\n\nSecondly, think about this:  humans and our ancestors have had millions of years to develop such features, if it were in fact possible, but it has NOT happened.  Why not?  Because there is no SELECTIVE ADVANTAGE for the human species of men acquiring these features and abilities. \n\nThird, there ARE cases of individuals that receive extra SEX chromosomes (look up Klinefelters and Turner' syndrome, for example) where individuals are born with XXY and XYY.  XXY individuals, as a rule, are infertile and can not produce children.  XYY individuals are fertile but are phenotypically male and do not develop uteruses and other features necessary to become impregnated.  So even in the cases of chromosal conditions that might perhaps favor male pregnancy, we do not observe males with the ability to be so.\n\nSo, IF a male had eggs they could not be fertilized because there is no way that the design of a male can receive semen into the genetalia.  But even if this were possible, there would be no place for the fertilized eggs to implant.  And if even they could implant, they couldnt grow because estrogen and progesterone are not present in high enough quantities in males to prepare the uterus (high levels of these hormones would have produced a female during development of the fetus).  This all boils down to the simple and obvious reality that males can not become pregnant.\n\nSomeone might perhaps argue, well it would be possible if certain mutations occurred.  This also is false.  Why?  Because evolution is a process that moves down a one-way street.  While such capability is present in lower organisms, higher animals are too specialized to be capable of such a transformation.  Even if all the proper sets of supposed mutations had amassed in one organism, that organism would either (one) not survive and be spontaneously aborted in utero, or (two) be born as an infertile individual.  Again, only lower animals with less well specialized sexual reproductive organs are capable of self-fertilization and "pregnancy" (flowering plants, for example, are capable of this).\n\nFinally, a genotypic male could undergo gender reassignment and become female, but a uterus and other "equipment" would have to be transplanted and various hormones taken.  I imagine, in theory, that this individual would be capable of becoming pregnant but in this scenario "he" is no longer "male".  \n\nGood question, but the answer is NO!
234681
This is a large question, and the source of much controversy, conflict, anger, and hilarity for all of recorded history. Aristophanes' Lysistrata is merely one of the earliest in a long literary tradition exploring the question. James Thurber is only one of the most recent, and funniest, of those writing in English.\n\nOnly in the last few decades has there been any scientific evidence which even begins to explain why the so long observed differences exist. \n\nIt is clear that there are, on average, anatomic differences between female and male brains. For instance, in the connection between the two hemispheres. And imaging studies of working brains ('PET scans') have shown some apparently characteristic differences in the areas of the brain used by males and females when their brains are ostensibly doing the same thing. There is even enough of such evidence that there are now centers for the study of gender differences. \n\nFrom a behavioral viewpoint, the field of evolutionary psychology (or sociobiology) has produced a series of testable hypotheses about differences between female and male behavior. These are essentially unique in the field because they suggest experiments which can test them. Thus far, this approach has shown promise in accounting for some of the non-cultural non-religious behavior differences. Thus far, even such things as the clothing styles chosen when going to dance clubs have been accounted for to some extent by this approach. Much of this work is controversial amongst one or another group since it deals with issues (eg, sex, reproduction, mating behavior, ...) which are of great importance socially or religiously.\n\nThe most reasonable account of behavioral differences between the sexes is based on reproductive success. Males who behaved this way (or these ways) tended to have more descendants (more children who survived to have children themselves), and females who behaved that way (or those ways) also had more children who survived to have children of their own. Much of the reasoning on these matters is based in the fact that, in humans, females cannot have more than a small number of children, given the underlying biology. We humans are born far from able to cope with life, and require a long period of maturation before we can. We share some of this extended infancy with some other species (such as chimpanzees and orangutans) and, to some extent, they show similar sex linked behavioral differences. Males, on the other hand, are capable of having a great many children. But, because of the long term helpless infancy period, together with typical human female awkwardness during much of pregnancy, it seems likely that males who stayed with the female increased the chances that children (half of whose genes came from him) were more likely to survive to child-bearing age. This pattern may also account for male jealousy (only if the female is sexually exclusive can he be sure the child is his) and female interest in male resource control. If he's rich (however rich is measured in a society), he will likely be able to increase the chance that her children will survive to have children of their own. Some of these suggestions (hypotheses) are subject to test in humans and some other species; the evolutionary approach has illuminated some hitherto opaque behaviors.\n\nThese matters are very near to the center of much conflict in traditional (and some other not so traditional) societies, many of whose citizens are made uneasy by new and different behaviors and by research which either 'endorses' some of those behaviors or 'undermines' some of their existing or traditional behaviors. In fact, the science is still in its infancy, and those who claim it endorses this or that don't understand it, and those who fear the science would be better advised to concentrate on policy makers of various kinds who don't understand the nature of science, nor much of this emerging scien
878053
Gender traits, are they  learned or are they hereditary?
193025
kinda throws a kink in the debate about homosexuality hermaphrodites can be either male or female only a genetic test at the beginning of their life can tell as they get older and go through puberty their true sex becomes evident