Do all fetus begin with XX chromosomes?
148814
No. Don't confuse the common phrase that "we all start as female" with the individual set of chromosomes. XY embryos are male; the "activation", so to speak, of the factors that will lead that individual to have male characteristics (gonads, genitalia and secondary sexual characters) occurs some time after the start of embryonic development. Thus if one examines an earlier embryo, males are indistinguishable from females.\nBut they each have their XX (females) or XY (males) sexual chromosome pair, and the proteins coded in their genome will lead to normal development of either sex.
227650
There is a syndrome called Klinefelters.\nHere, a male will have chromosomes XXY,\nand more than likely will appear from the outside to be female.  The genitals don't develop as a normal males, sometimes looking like he has female organs.  Cases such as these usually end up with the biological boy to be raised by a girl, and may even grow breasts during puberty.  For some klinefelters people, their masculine characteristics can appear during puberty or adulthood.  These women, are now resembled as men, and even their genital areas can develop into that of typical males, thus a woman turning into a man.  So some of the stories about women turning into men in history are true in a sense, although these women were not completely biologically female to begin with.
243784
It is haploid, only having 23 chromosomes until it is fertilized. Then it is diploid with 23 pairs(46 total) of chromosomes, and is capable of growing into a baby.
262065
During your 5th week of pregnancy (fetal age is 3 weeks..since conception occurs around week 2. ) the heart begins to beat.  The fetus grows very quickly during the stage...though the size of a lentil bean\n\nFrom Baby Center: How your baby's growing: Deep in your uterus your embryo is growing at a furious pace. At this point he's about the size of a sesame seed, and he looks more like a tiny tadpole than a human. He's now made up of three layers — the ectoderm, mesoderm, and endoderm — that will later form his organs and tissues. The cells are forming for his major organs, including his kidneys and liver, and his neural tube is beginning to develop. This neural tube — from which your baby's brain, spinal cord, nerves, and backbone will sprout — develops in the top layer, called the ectoderm. This layer will also give rise to his skin, hair, nails, mammary and sweat glands, and tooth enamel. His heart and circulatory system begin to form in the middle layer, or mesoderm. (This week, in fact, his tiny heart begins to divide into chambers and beat and pump blood.) The mesoderm will also form your baby's muscles, cartilage, bone, and subcutaneous (under skin) tissue. The third layer, or endoderm, will house his lungs, intestines, and rudimentary urinary system, as well as his thyroid, liver, and pancreas. In the meantime, the primitive placenta and umbilical cord, which deliver nourishment and oxygen to your baby, are already on the job.
832734
A karyotype can tell two sorts of information to a genetic counselor about an unborn child. First, it can show the sex of the child (XX=girl, XY=boy). Secondly, it can tell the counselor if there are any chromosomal abnormalities with the unborn child. One more common abnormality seen is Down's Syndrome, which occurs from an extra # 13 chromosome. Turner's Syndrome is when there is only one X sex chromosome. Klienfelter's Syndrome occurs when a fetus inherits 2 X and 1 Y sex chromosome (XXY). Patau's Syndrome is an extra # 18 chromosome. These are the sorts of things a karyotype can tell a genetic counselor.\nGood luck with your assignment!
398876
it's 50 50 every time.  genetics states that you get one chromosome from your mom (always X) and one from the dad, X or Y.  XX means girl, XY means boy. (assuming dad has even amounts of both).\n\nHence you use condition probablity assuming each occurance is a 50% chance.\n\n50% x 50% x 50% = 12.5%
60697
The Straight Dope says, "To tell you the truth, nobody really knows. The best explanation I've been able to find (and frankly it doesn't explain very much) is that nipples aren't a sex-linked characteristic. In other words, nipples are just one of those sexually neutral pieces of equipment, like arms or brains, that humans get regardless of sex." \n\nIt's also notable that the fetus starts to develop nipples long before any other sex-linked characteristics.
460679
XXY is called Klinefelter's Syndrome. Individuals with Klinefelter's are male instead of female, and they are almost always sterile.
40538
So what will they do, I know there are people born with both organs of male and female.. How will you do this? Very interesting...
656270
having xxx sex chromosome.or a female with turner syndrome
1123588
During pregnancy, the fetus inside the womb undergoes constant change in formation before finally being born.  All fetuses start off female, and require an extra hormone (XY chromosome) to start forming into a male.  So the nipples form before the male hormones are sent to the fetus.\n\nThere is one point in pregnancy where the fetus resembles a fish-like stage.  This is why humans have webbing in fingers and toes.  Crazy stuff, huh?
645957
All human embryos in the womb look the same externally, until testosterone is either added or not.  If not, the baby will develop physically as a girl, if the testosterone is added, the baby develops physically as a boy.  This is true regardless of the XX or XY chromosome of the baby.  The nipples develop prior to the addition of the testosterone.\n\nThey are there because the child could have developed as a woman, and the only purpose that I can think of that they have for men is perhaps a little thrill when your lover pinches them. :)
153971
My guess is that they had first-trimester miscarriages.  It could just be coincidence.  It could also be that for whatever reason you have a relatively high number of defective sperm (no offense), or maybe your genetically defective sperm swim extra fast for some reason.  I'm just guessing here, but it seems to me that some individuals could be at a higher risk for nondisjunction events (when homologous chromosomes fail to separate) with results in trisomies and monosomies (the sperm has the wrong number of chromosomes, so the embryo has the wrong number of chromosomes).  Trisomy 21 causes Downs Syndrom, and I think there are one or two others that can result in full-term babies, but most of them self-abort in the first trimester.  If I'm right, it could also explain your fertility issues.  However, I want to make perfectly clear that this is just the speculation of a first-year bio major and shouldn't be taken as an authoritative answer!\n\nPS.  I think it's a really cool thing to have picked up on, and there's a very good reason your doctor didn't go into research. :)
974272
The word Fetus....after the 8th week of gestation.\nEmbryo is up to the 8th week.\nMost terminations are performed prior to the 8th week.  Not that it would matter in you strong opinion...just stating a fact.\nI think the more important question is:    "WHEN DOES LIFE BEGIN"
430415
To answer your question....yes.  The egg cells of the female all carry X chromosomes.  The sperm cells can carry either X or Y.  So basically, the sex of a mammal depends on the male, and which particular sperm fertilizes the egg (X).  If an X sperm fertilizes the egg, you have XX, which is a female, and if a Y sperm fertilizes it, you have XY, which is male.  This is why some sex-linked traits are more visible in males, such as color blindness, but that's a whole different post.
1073362
AFAIK, the Barr Body derives from the "spare" X chromosome that female mammals carry in (most of) their cells.  For example, we women inactivate one of our 2 X chromosomes, quite early in embryonic life.  From then on, tissues use the genes on one or the other, but not both.  The inactivated one sits aside in the nucleus, looking condensed.\n\nI think of it like the wallflower, at a dance; the girl left over...\n\n:-P\n\nAnyhow, men generally have just one X, so have no Barr Body.  Men with Klinefelter Syndrome have XXY, and have a Barr Body.\n\nThe number of X chromosome, minus one = number of Barr bodies.\n\nSome people have lots of X chromosomes, eg XXX, XXXX, etc, and the numerical rule applies.\n[AFAIK; it is a while since I studied this!]\n\n:-)
1051925
~~Fetal Development~~\nDevelopment of the Embryo and Fetus\n\nOverview\n\n* Did You Know?\nPregnancy is counted from the first day of the mother's last period. This means that at conception, the unborn child is already considered two weeks old.1 \nFirst Trimester \n \nWeek 2* Conception is the moment at which the sperm penetrates the ovum. Once fertilized it is called a zygote, until it reaches the uterus 3-4 days later. \n1st trimester photos\n \nWeek 4 The embryo may float freely in the uterus for about 48 hours before implanting. Upon implantation, complex connections between the mother and embryo develop to form the placenta. \nWeek 6 The embryo is about 1/5 of an inch in length. A primitive heart is beating. Head, mouth, liver, and intestines begin to take shape. \nWeek 10 The embryo is now about 1 inch in length. Facial features, limbs, hands feet fingers and toes become apparent. The nervous system is responsive and many of the internal organs begin to function. \nSecond Trimester\n  \nWeek 14 The fetus is now 3 inches long and weighs almost an ounce. The muscles begin to develop and sex organs form. Eyelids, fingernails, and toenails also form. The child's spontaneous movements can be observed. \n2nd trimester photos  \nWeek 18 The fetus is now about 5 inches long. The child blinks, grasps, and moves her mouth. Hair grows on the head and body. \nWeek 22 The fetus now weighs approximately 1/2 a pound and spans about 10 inches from head to toe. Sweat glands develop, and the external skin has turned from transparent to opaque. \nThird Trimester \n \nWeek 26 The fetus can now inhale, exhale and even cry. Eyes have completely formed, and the tongue has developed taste buds. Under intensive medical care the fetus has a over a 50% chance of surviving outside the womb. \n3rd trimester photos \nWeek 30 The fetus is usually capable of living outside the womb and would be considered premature at birth. \nWeek 40 This marks the end of the normal gestational period. The child is now ready to live in outside of his mother's womb.