I work (transcribe) for 5 pathologists here in the US and they all say the X Y chromosomes are the factors of being born a male or female. It’s true, that homosexuals are really born that way. They can’t help it. It’s no one’s fault. No one should hate them for being born that way. When my kids grow up, I would hope they wouldn’t turn out to be gay, but if they do, I wouldn’t love them any less, because I know it would be because they couldn’t help it; thats the way their were born. We all start off with X chromosome (XX which is female) and (XY which is male). The SRY gene plays the key step in switching that X to a Y. Some switch totally (men who or not gay) and some still carry the X trait (which might be bi-sexual) and works the same for homosexual woman as well. Besides the male/female traites, rare cases, about 1 in 2,000, are born with both male and female genitals. I’ve seen two babies this year born with both genitals and the Pathologist has to go and get samples to study if they have more female or male traits to determine for the surgeon as to which one to fix.
Their study below is what happens to the X and Y chromosomes during birth.
The complete set of chromosomes in the cells of an organism is its karyotype.
The karyotype of the human female contains 23 pairs of homologous chromosomes:
22 pairs of autosomes
-1 pair of X chromosomes
The karyotype of the human male contains:
the same 22 pairs of autosomes
-one X chromosome
-one Y chromosome
(A gene on the Y chromosome designated SRY is the master switch for making a male.)
What is the evidence?
On very rare occasions aneuploid humans are born with such karyotypes as XXY, XXXY, and even XXXXY. Despite their extra X chromosomes, all these cases are male.
(and thus, they should be female), however, they have a male phenotype. This is because they are transgenic for SRY. Fertilized XX eggs were injected with DNA carrying the SRY gene.
Another rarity: XX humans with testicular tissue because a translocation has placed the SRY gene on one of the X chromosomes
Still another rarity that demonstrates the case: women with an XY karyotype who, despite their Y chromosome, are female because of a destructive mutation in SRY.
The X chromosome carries hundreds of genes but few, if any, of these have anything to do directly with sex. However, the inheritance of these genes follows special rules. These arise because males have only a single X chromosome almost all the genes on the X have no counterpart on the Y; thus
any gene on the X, even if recessive in females, will be expressed in males.
Genes inherited in this fashion are described as sex-linked or, more precisely, X-linked.
X-Inactivation
Human females inherit two copies of every gene on the X chromosome, whereas males inherit only one (with 18 exceptions: the 9 pseudoautosomal genes and the 9 “housekeeping” genes found on the Y).
During interphase, chromosomes are too tenuous to be stained and seen by light microscopy. However, a dense, stainable structure, called a Barr body is seen in the interphase nuclei of female mammals. The Barr body is one of the X chromosomes. Its compact appearance reflects its inactivity. So, the cells of females have only one functioning copy of each X-linked gene - the same as males.
X-inactivation occurs early in embryonic development. In a given cell, which of a female’s X chromosomes becomes inactivated and converted into a Barr body is a matter of chance. After inactivation has occurred, all the descendants of that cell will have the same chromosome inactivated. The X-inactivation creates clones with differing effective gene content. An organism whose cells vary in effective gene content and hence in the expression of a trait, is called a genetic mosaic.
Mechanism of X-inactivation
Inactivation of an X chromosome requires a gene on that chromosome called XIST.
XIST encodes a large molecule of RNA. XIST RNA accumulates along the X chromosome containing the active XIST gene and proceeds to inactivate all, or almost all of the other hundreds of genes on that chromosome.
XIST RNA does not travel over to any other X chromosome in the nucleus.
Barr bodies are inactive X chromosomes “painted” with XIST RNA.
During the first steps of embryonic development of the female, the XIST locus on each of her two X chromosomes is expressed but the XIST RNA is quickly broken down. Then something happens to tip the balance in favor of one or the other of the X chromosomes. Transcription continues on one of the X chromosomes, leading to an accumulation of XIST RNA and converting that chromosome into an inactive Barr body.
Transcription of XIST ceases on the other X chromosome allowing all of its hundreds of other genes to be expressed. The shut-down of the XIST locus on the active X chromosome is done by methylating XIST regulatory sequences. DNA methylation usually results in gene repression so methylation permanently blocks XIST expression and permits the continued expression of all the other X-linked genes.
X-inactivation in the female embryo appears to be entirely random. There is no predicting whether it will be the maternal X or the paternal X that is inactivated in a given cell. But that is not the case for her extraembryonic membranes (that go on to form the amnion, placenta, and umbilical cord). In all the cells of the extraembryonic membranes, it is father’s X chromosome that is inactivated.
Some genes on the X chromosome escape inactivation.
X-Chromosome Abnormalities:
People are sometimes found with abnormal numbers of X chromosomes. Unlike most cases of aneuploidy, which are lethal, the phenotypic effects of aneuploidy of the X chromosome are usually not severe. Examples:
Turner’s syndrome: females with but a single X chromosome. The phenotypic effect is mild because their cells have a single functioning X chromosome like those of XX females. Number of Barr bodies = zero.
XXX, XXXX, XXXXX karyotypes: all females with mild phenotypic effects because in each cell all the extra X chromosomes are inactivated. Number of Barr bodies = number of X chromosomes minus one.
Klinefelter’s syndrome: people with XXY or XXXY karyotypes are males (because of their Y chromosome). But again, the phenotypic effects of the extra X chromosomes are mild because, just as in females, the extra Xs are inactivated and converted into Barr bodies.
I hope this helps you guys understand. I transcribe daily and it makes sense to me working in Pathology. Really, these people, I’m sure didn’t ask to be born that way, but by chance, their chromosome makeup didn’t switch over. It’s not their fault; nor anyone elses; it’s the way they were born.
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