I saw the news, according to Reuters - Several hundred thousand opponents of same-sex marriage marched in central Paris on Sunday. I did not expect that the French people who are so romantic nation actually value the genders so much. The Nation, who owns the Charles de Gaulle the greatest man in human history, loses the past glory immediately in my heart. It reminds me that the vast majority of people are always stupid in human history, whatever in west or east. So today, I want to have a look at how we define the female and male, and what exactly control the sex determination.
All living things reproduce. Reproduction is the process of generating offspring. There are only two types of reproduction: sexual and asexual, whatever animals or plants. Here I am not going to see the differences, advantages or disadvantages of sexual and asexual reproduction, and this chapter only focuses on how sex determination.
1，Apparently,
higher organisms have resorted to sexual reproduction in spite of its
complexity, although sexual reproduction involves more time and energy. Most animals and some plants have two genders,
and sex-determining mechanism in different types of organisms is a big
difference. How is gender determined in an organism? It is actually determined
in different ways. It is broadly divided into two main categories: temperature-dependent
sex determination (TSD) and genotypic sex determination (GSD).
TSD: Precisely speaking, the temperature-dependent
sex determination is just one of the non-genetic sex-determinations. Many other sex-determination
systems exist. In some species of reptiles, including alligators, some turtles,
the tuatara, sex is determined by the temperature at which the egg is incubated
during a temperature sensitive period. The temperatures required for the specific sexes
are known as the female promoting temperature and the male promoting
temperature. When the temperature stays near the threshold during the
temperature sensitive period, the sex ratio is varied between the two sexes. For
example, in sea turtles, warmer temperatures produce more or all females, cool
temperatures produce more or all males, and the pivotal temperature is the constant
incubation temperature that produces equal numbers of males and females. TSD
also occurs in other reptiles (crocodilians, some freshwater and land turtles,
some lizards), some types of fish, some types of invertebrates, etc.
In TSD animals, how do we define the genders? Apparently,
the only way we define it is depending on sex expressive traits, because the
same genders may not share the same sexual genes.
GSD:
Genotypic sex determination occurs when sex is established by genetic factors
(e.g. sex chromosomes) at conception and it has two main types: XX/XY and
ZW/ZZ. The XX/XY sex-determination system is the most familiar, as it is found
in humans. In the system, females have two of the same kind of sex chromosome
(XX), while males have two distinct sex chromosomes (XY). The XY sex
chromosomes are different in shape and size from each other, unlike the autosomes.
Some species (including humans) have a gene SRY on the Y chromosome that
determines maleness. The ZW sex-determination
system is found in birds, reptiles, some insects and other organisms. The ZW
sex-determination system is reversed compared to the XY system: females have
two different kinds of chromosomes (ZW), and males have two of the same kind of
chromosomes (ZZ). In the chicken, this was found
to be dependent on the expression of DMRT1. In birds, the genes FET1 and ASW
are found on the W chromosome for females, similar to how the Y chromosome
contains SRY. However, not all species depend upon the W for their sex. Because the use of ZW sex determination is varied,
it is still unknown how exactly most species determine their sex. I roughly
agree that God always finds a way, when he determines to do something.
In XX/XY system, Y chromosome evolved from X chromosome,
in contrary in WZ/ZZ system, W evolved from Z chromosome. In the history of
long evolution, some genes on Y and W chromosomes have been partially degraded，so Y or
W chromosome can’t synthesize the normal sex organ independently.
In GSD animals, how do we define the genders? If
you think the one who has penis is a male, what about the birds with WZ
chromosomes and fish? There is no big difference between two sexes, because
neither sex has penis. Birds choose cloaca kiss to fertilize, and fish
basically are in vitro fertilization. Even in mammals, you can not easily define
genders.
2，Next, we
are going to see some special examples in mammals which people call as abnormality.①Freemartin:
A freemartin or free-martin
is an infertile female mammal which has masculinized behavior and
non-functioning ovaries. It is genetically female, but has many
characteristics of a male. The ovaries of the freemartin do not develop
correctly, and they remain very small. Also, the ovaries of a freemartin do not
produce the hormones necessary to induce the behavioral signs of heat. The
external vulvar region can range from a very normal looking female to a female
that appears to be male. Usually, the vulva is normal except that in some
animals an enlarged clitoris and large tufts of vulvar hair exist. In short, these
animals often have a masculine steer-like appearance, but with XX chromosomes.
The cause of this disease
is, in most cattle twins, the blood vessels in the
chorions become interconnected, allowing blood from each twin to flow around
the other. If a fetus has XX chromosomes, the lack of testosterone production
during gestation will allow her to develop female external and internal
genitalia. Male animals develop differently in the womb because their XY
chromosomal arrangement causes them to produce testosterone. This hormone
inhibits female reproductive tract development. When mixed sex twins are
developing, it is possible for the blood vessels within the two placentas so
fuse and form a common circulation. When this happens, the testosterone
produced by the male calf is able to circulate to the female twin and affect
her sexual differentiation. If both fetuses are the same sex this is of no
significance, but if they are different, male hormones pass from the male twin
to the female twin. It also occurs occasionally in other mammals including
sheep, goats and pigs.
The key word: the twins
shared the same placenta and the female one was affected by the testosterone
from the male one. I guess if a fertilized egg was injected by outside testosterone
from the beginning, the female babies always have masculine vulva. In other
words, if male really has a uterus, is he appropriate to have a baby? I do think
scientists also can create artificial freemartin human. You could say I have a
daydream, but I have another perfect evidence to support my daydream - Spotted Hyena.
②Spotted Hyena
The female Spotted Hyena's urogenital system is
unique among mammals: there is no vagina, and the clitoris is as large and as
erectile as the male's penis - only the shape of the glans makes it possible to
tell the sexes apart. In the case of female spotted hyena, the vulva is fused,
and the clitoris is used for urination, mating (when the clitoris contracts,
while the opening widens to allow penetration) and giving birth. When spotted
hyaenas mate, the male inserts his erect phallus into the female's flaccid one.
Another curious fact about female spotted hyenas, which scientists have
confirmed, is that they carry higher levels of testosterone than the males in
their blood, and this is something that can be observed as early as the embryo
stage. That's why biologists initially believed that the development of the
clitoris was caused by the huge quantities of testosterone to be found in the
fetus.
The key words: female spotted hyenas have higher
levels of testosterone than the males and the baby girl who lived in the mother’s
body like this must inevitably be led to masculine vulva. This point can be understandable.
In long history of spotted hyena evolution, she has already known how to get
along with that external factor in peace and evolved a special reproductive
system under that. I think we can do an experiment like this: have an artificial
insemination spotted hyena, and then put this zygote into normal dog’s uterus,
and see what the female baby dog’s vulva looks like? We will know whether it is
affected by mother or not? I bet the little female dog is goint to have a normal
feminine vulva, but infertility. The influence from mother to child or between
the twins is not just limited to the sex hormone, and they also can exchange
the cells.
③ChimeraHere I don’t want to talk about "chimera" in Greek mythology where it means a monster: part goat, part lion, part snake. In human biology, a chimera is an organism with at least two genetically distinct types of cells -- or, in other words, someone meant to be a twin. But while in the mother's womb, two fertilized eggs fuse, becoming one fetus that carries two distinct genetic codes -- two separate strands of DNA.
So far the case of Lydia Fairchild is the most famous case in U.S., and it turned out she's a chimera which is a fusion of non-identical twins, and the best thing of this case is to make lots of researchers started to pay attention to chimera on human. Here I have another big question: where are the non-identical twins from? Apparently, chimera must be a fusion of non-identical twins, and there is no cells exchange problem in identical twins, because no matter they exchange the cells or not, they always share the same genes, and you can’t find out. What about fraternal twins? But fraternal twins each have their own placenta and own amniotic sac, two different placenta means they both directly exchange everything with the mother, and two different amniotic sac means they don’t have any chance to exchange anything to each other. I think the fraternal twins are very hard to fuse together, so we can easily find that those conjoined twins are identical twins, at least so far we don’t find any conjoined twins are from traditional fraternal yet, and I also think the fraternal twins are very hard to affect each other, otherwise we must can find lots of fraternal female twin’s vulva masculinization, due to her brother’s androgens.
In the uterus, a majority of monozygotic twins (60–70%) share the same placenta but have separate amniotic sacs. In 18–30% of monozygotic twins each fetus has a separate placenta and a separate amniotic sac. A small number (1–2%) of monozygotic twins share the same placenta and amniotic sac. Fraternal twins each have their own placenta and own amniotic sac.
Microchimerism (abbreviated Mc) is the presence of a small number of cells that originate from another individual and are therefore genetically distinct from the cells of the host individual. Microchimerism in humans commonly happens during pregnancy. Cells from the fetus' immune system can enter the mother through the placenta, where they may survive and continue to reproduce through mitosis. In some cases, the descendants of these fetal cells remain in the mother decades later. The same process in reverse can result in populations of maternal immune cells living in the fetus, though this is less common. I think as time goes by, microchimerism will be observed in many tissues and organs in our human. Here I want to illustrate that freemartin doesn’t mean she is a microchimerism, maybe her vulva development is just interfered by androgens from her brother, but she is not a chimera at all. I just make a guess, what I want to say is they are not necessary and sufficient conditions. Same logic to Spotted Hyena. I want to emphasize that If the Microchimerism between mother and child really happens generally, I think we should reconsider the surrogacy very carefully.
No matter what type of the twins, they always have to exchange things with the mother, so we can understand the chimera between child and mother, but what about the chimera between the twins? I think we have to know another Interesting case – polar twins.
④Semi-identical twins
According to BBC news, Scientists have revealed details of the world's only known case of "semi-identical" twins. Researchers have discovered a pair of twins who are identical through their mother's side, but share only half their genes on their father's side.
Researchers investigated the twins' genetic makeup because one was born with ambiguous genitalia. This twin turned out to be a 'true hermaphrodite', with both ovarian and testicular tissue. The other twin is anatomically male. Genetic tests revealed that each twin contained some 'female' cells with two X chromosomes, and some 'male' cells with an X and a Y. The proportion of each type varies from tissue to tissue in each twin, the researchers report in Human Genetics. So scientists gave the explanation is that the 'semi-identical' twins are the result of two sperm cells fusing with a single egg — a previously unreported way for twins to come about, say the team that made the finding.
Frankly speaking, I do not agree with the interpretation like that. The explanation they gave depends on two evidences: one is the twins both are chimaeras, and the other is one of the twins was born with ambiguous genitalia and turned out to be a 'true hermaphrodite' with both ovarian and testicular tissue. I think these two points are insufficient to support the conclusion they gave. Here I can give you another story depending on these two points.
We
have to recall Meiosis first. In humans (and most vertebrates), the first polar
body does not go on to meiosis II, but the secondary oocyte does proceed as far
as metaphase of meiosis II and then stops. Only if fertilization occurs will meiosis II ever be completed. Entry
of the sperm restarts the cell cycle. In principle, polar bodies are fertilized by sperm,
even if the egg cell and a polar body were both fertilized by separate sperms.,
further development would usually not occur because the zygote formed by the
fusion of the sperm and polar body would not have enough cytoplasm or stored
nutrients to feed the developing embryo. The following figure is a normal
process of meiosis and fertilization:
One
egg × One sperm
I don’t know what the key it is to decide which lucky half can win all cytoplasm and which poor half genes have to dies due to uneven splitting of the cytoplasm, but I believe competition is everywhere. Once the game is evenly matched, the first polar body also gets some cytoplasm as much as secondary oocyte. The following figure is an even splitting during meiosis I, but uneven splitting during meiosis II. Due to the two sperm are random, so they share 50% identical genes to each other. Don’t forget homologous chromosomes segregate from each other during meiosis I, so the two eggs share 0% identical genes. The result is the twins share no genes on their mother's side, but only half their genes on their father's side. Maybe we can call them “Quarter identical twins”.
Two
eggs(share 0% identical genes) × Two
sperm(share 50% identical genes)
Two eggs(share 100% identical genes) × Two
sperm(share 50% identical genes)
Four
eggs × Four sperm(share 50% identical genes)
I think the case of Lydia Fairchild is not closed, we can check the two different sets of genes on her body, and then we can figure out what kind of twins before they fused. Above three examples are female were interfered by the male hormone more or less, but sometimes androgen got the bad luck.
⑤AIS:
Androgen insensitivity syndrome (AIS), formerly known as testicular feminization, is an X-linked recessive condition resulting in a failure of normal masculinization of the external genitalia in chromosomally male individuals. This failure of virilization can be either complete androgen insensitivity syndrome (CAIS) or partial androgen insensitivity syndrome (PAIS), depending on the amount of residual receptor function. In short, these defects make the body unable to respond to the androgens that produce a male appearance.
Human embryos develop similarly for the first six weeks, and the indifferent gonads begin to differentiate according to genetic sex. If the karyotype is 46, XY, testes develop due to the influence of the Y chromosome's SRY gene. This process does not require the presence of androgen, nor a functional androgen receptor. Then in the next process, what if mutation happens in the AR gene and the function of the androgen receptor (AR) is impaired. This gene provides instructions for making a protein called an androgen receptor. Androgen receptors allow cells to respond to androgens, which are hormones (such as testosterone) that direct male sexual development.
Apparently, the example of freemartin illustrates that, due to the exterior strong hormone (testosterone) interference, despite the presence of ovarian, the accessory sex glands still go to the direction of male, but the genotype is 100% sure of XX. Conversely, the example of AIS illustrates that, when the expression is blocked, despite the presence of testosterone, the accessory sex glands still go to the direction of female, but the genotype is 100% sure of XY.
Individuals with CAIS are raised as females. They are born phenotypically female and almost always have a heterosexual female gender identity; the incidence of homosexuality in women with CAIS is thought to be less than unaffected women. Because of this, we can get if the gay genes really exist on chromosomes, it doesn't have any concern with sex chromosomes.
The two examples of freemartin and AIS can apparently illustrate that together, in mathematics, the sexual expression which controlled by gene is a piecewise function. First step, the gonad (testes or ovaries) is synthesized by SRY on the Y chromosome or by some genes on X chromosome. Of course, in mammals, the genes which control the expression of testis are completely dominant genes, compared to the genes which control the expression of ovarian. Second, some specific hormones, released by testes or ovaries, control the growth direction of other accessory sex glands, whether labia fused or not, the clitoris shaft became big and wrapped urethra or not, the gonad descend or not. This two steps both control a person whether abnormality or not step by step.
In GSD animals, how do we define the genders? We should define it depending on sex genotype or expressive traits? If we choose expressive traits to distinguish the two genders, does it depend on gonad, primary sex characteristics, or secondary sexual characteristics? It is very complicated to classify on this issue.
3, Another thorny issue: hermaphrodite
①From the view of genes
As long as there are two different sex alleles on your chromosomes, you can be identified as hermaphrodite. In other words, if your sex genes are not homozygote, you are hermaphrodite. In my theory, male with XY chromosomes in mammals and female with ZW chromosomes in birds are all hermaphrodites. The reason, why sometimes testis genes become dominant genes in some species and sometimes ovarian genes become dominant genes in some other species, all depends on the environment of the sex genes, not only the natural environment, but also the genes environment. Apparently, the environment in birds determined that ovarian gene is dominant, but recessive in mammals. Anyway, whatever the environment determined which sex genes is dominant, it doesn’t change they are hermaphrodites from the gene view. XY and WZ are both Heterozygous in sex genes.
②From the view of sex phenotype
Compared to birds and fish with simple reproductive system, mammals have more complicated system. For example the difference between male and female in birds and fish is just in gonad, but no big much difference in the vulva between the sexes, so I think that is why sex reversal always happen on fish. In mammals, because the vulva between the sexes is very different, there is no chance to make sex reversal at all. So I think it can be divided into three different situations.
Gonad: As long as the testis and ovary both exist, we can call them as hermaphrodite. This case basically can’t happen on animals, but only some plants. Some flowers that contain both sexual flower parts (stamen and pistil) are called perfect or bisexual while those that contain either stamen or pistil only are called imperfect or unisexual flowers, regardless of whether they lack sepals or petals. We can call this case as true hermaphrodite, and I think it can’t happen on human, except for chimera under one condition two different cells in primary gonadal. Flowers with both stamens and a pistil are capable of self-fertilization, which does increase the chance of producing seeds but limits genetic variation. The separation of the male and female sexual organs increases the possibility of outcrossing or cross pollination.
Subsidiary structure: The cases like freemartin and AIS which have the subsidiary structures of the other gender because of some accidents. A genes of XX with female ovarian, but male vulva, or a genes of XY with male testis, but female vulva. How do we define the two genders now? I don’t think we should consider them as hermaphrodite.
Shemale: Famous shemales are always from Thailand, and most of them were from poor families and injected external estrogen when childhood. As a woman, I have to say some shemales are really pretty, I can’t help myself looking at them. They still have XY male genes, testis, normal male vulva and all normal male primary sex characteristics, but female secondary sex characteristics due to man-made after birth. Injection estrogen from outside only can change the secondary sex characteristics, but can’t change the genes, gonad and other accessory sex glands. How do we define them? Male? Female? Or hermaphrodite?
③Sex reversal
Sex reversal is very common in fish. Fish that can alter their sex are known as successive hermaphrodites. Normally the sex reversal occurs only once. For example, a sexually mature female reproduces and then becomes a male. The ovaries shrink, the fish develops testes, and male hormones are released. These physiological changes also alter the animals’ behavior. New males become aggressive, defend territory, and court females. In China's countryside, occasionally the kind of thing that hen becomes cock happens, but we never heard that cock becomes hen over night. Why? What if in some fish whole life, they don’t have sex reversal? Should we call them as hermaphrodite? Whatever they have sex reversal or not, their genes never change, right?
4, What are the genders exactly?
What can we learn from above? Do you lose yourself in my words? What is homosexuality? What is heterosexuality? Before we define someone is homosexual or heterosexual, we have to figure out how should define the two genders. What about the birds with WZ chromosomes and fish? There is no big difference between two sexes, because neither sex has penis. Birds choose cloaca kiss to fertilize, and fish basically are in vitro fertilization. Our human can’t even define the genders clearly, not to mention homosexual or heterosexual. Homosexuality is simply a false proposition.
Richard Dawkins wrote his opinion about genders in his book - The selfish gene “We simply accepted that some animals are called male, and others female, without asking what these words really meant but what is the essence of maleness? What, at bottom, defines a female? We as mammals see the sexes defined by whole syndromes of characteristics - possession of a penis, bearing of the young, suckling by means of special milk glands, certain chromosomal features, and so on, These criteria for judging the sex of an individual are all very well for mammals but, for animals and plants generally, they are no more reliable than is the tendency to wear trousers as a criterion for judging human sex, In frog, for instance, neither sex has a penis. Perhaps, then, the words male and female have no general meaning. In gene’s long journey down the generations therefore, an average gene will spend approximately half its time sitting in male bodies, and the other half sitting in female bodies.”
I do think our humans like to classify too much, fat and thin, high and short, white and black, man and woman, but we really ignore something very rare – true love. In long history of evolutionary: sexual reproduction showed up first; then penis intercourse, we have to admit that until now there some animals on earth that can reproduce but no penis intercourse, like IVF in fish or cloaca kiss in birds; and then marriage, until now I don’t think not every marriage is because of love, especially in patriarchal society, the purpose a woman get into a marriage is for survival, because women can’t go to school like boys, can’t go out to work like man, but only marriage for living; finally love, to be honest, I do not think love is necessary in evolutionary. The only purpose of non-human having intercourse is only for reproduction, not for love. So far in lots of human being countries, men only care about the possessive quantity and quality of women, and women only care about how much interests one man can offer to her. This is just a sale, not love. The nature of this relationship is as same as clients and prostitutes. Unfortunately, I live in this dynasty.
Let's go back to genes, in my theory, the testis and ovary genes are just an ordinary two alleles as same as single eyelids and double eyelids genes on autosomal. Don’t tell me the reason you think someone with single eyelids can only marry someone with double eyelids, is just because they don’t share the same trait on eyelids. Our human, as only one intelligent life on earth, should see the essence of things through outward appearance. Every person has 46 chromosomes; in other words, do not let one chromosome which only occupied the probability of 2.17% covers your heart. Just love someone following your heart.
What is love? Love is simple, to be together. If one day, women can wake up from the daydream of self-deception to find their self-consciousness, nothing is going to prevent two people being together, no matter a man with a woman, or two women, or two men.
Love is being together.
By the way, I saw some news that female orgasms increase the chance of fertility, and women can have orgasms during child birth. I am almost so mad to hematemesis!!!
没有评论:
发表评论