Sexual differentiation in humans - wikipedia Sexual differentiation in humans The human Y chromosome showing the SRY gene which codes for a protein regulating sexual differentiation. Sexual differentiation in humans is the process of development of sex differences in humans. It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination. Sexual differentiation includes development of different genitalia and the internal genital tracts, breasts, body hair, and plays a role in gender identification. The development of sexual differences begins with the XY sex - determination system that is present in humans, and complex mechanisms are responsible for the development of the phenotypic differences between male and female humans from an undifferentiated zygote. Females have two X chromosomes, and males have a Y chromosome and an X chromosome. At an early stage in embryonic development, both sexes possess equivalent internal structures. These are the mesonephric ducts and paramesonephric ducts. The presence of the SRY gene on the Y chromosome causes the development of the testes in males, and the subsequent release of hormones which cause the paramesonephric ducts to regress. In females, the mesonephric ducts regress. Divergent sexual development, known as intersex, can be a result of genetic and hormonal factors. Contents 1 Sex determination 2 Reproductive system 2.1 Internal genital differentiation 2.2 External genital differentiation 3 Secondary sexual characteristics 3.1 Breast 4 Psychological and behavioral differentiation 5 Intersex conditions 6 Timeline 7 See also 8 Further reading 9 References 9.1 Sources Sex determination Main article : XY sex - determination system Most mammals, including humans, have an XY sex - determination system : the Y chromosome carries factors responsible for triggering male development. The `` default sex, '' in the absence of a Y chromosome, is female - like. This is because of the presence of the sex - determining region of the Y chromosome, also known as the SRY gene. Thus, male mammals typically have an X and a Y chromosome ( XY ), while female mammals typically have two X chromosomes ( XX ). In humans, biological sex is determined by five factors present at birth : the presence or absence of a Y chromosome, the type of gonads, the sex hormones, the internal genitalia ( such as the uterus in females ), and the external genitalia. Chromosomal sex is determined at the time of fertilization ; a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell. Gonadal sex refers to the gonads, that is the testis or ovaries, depending on which genes are expressed. Phenotypic sex refers to the structures of the external and internal genitalia. A human fetus does not develop its external sexual organs until seven weeks after fertilization. The fetus appears to be sexually indifferent, looking neither like a male or a female. Over the next five weeks, the fetus begins producing hormones that cause its sex organs to grow into either male or female organs. This process is called sexual differentiation. The precursor of the internal female sex organs is called the Müllerian system. Reproductive system Main article : Development of the reproductive system By 7 weeks, a fetus has a genital tubercle, urogenital groove and sinus, and labioscrotal folds. In females, without excess androgens, these become the clitoris, urethra and vagina, and labia Differentiation between the sexes of the sex organs occurs throughout embryological, fetal and later life. This includes both internal and external genital differentiation. In both males and females, the sex organs consist of three structures : the gonads, the internal genitalia, and the external genitalia. In males, the gonads are the testes and in females they are the ovaries. These are the organs that produce gametes ( egg and sperm ), the reproductive cells that will eventually meet to form the fertilized egg ( zygote ). As the zygote divides, it first becomes the embryo ( which means ' growing within ' ), typically between zero and eight weeks, then from the eighth week until birth, it is considered the fetus ( which means ' unborn offspring ' ). The internal genitalia are all the accessory glands and ducts that connect the gonads to the outside environment. The external genitalia consist of all the external reproductive structures. The sex of an early embryo can not be determined because the reproductive structures do not differentiate until the seventh week. Prior to this, the child is considered bipotential because it can not be identified as male or female. Internal genital differentiation The internal genitalia consist of two accessory ducts : mesonephric ducts ( male ) and paramesonephric ducts ( female ). The mesonephric system is the precursor to the male genitalia and the paramesonephric to the female reproductive system. As development proceeds, one of the pairs of ducts develops while the other regresses. This depends on the presence or absence of the sex determining region of the Y chromosome, also known as the SRY gene. In the presence of a functional SRY gene, the bipotential gonads develop into testes. Gonads are histologically distinguishable by 6 -- 8 weeks of gestation. Subsequent development of one set and degeneration of the other depends on the presence or absence of two testicular hormones : testosterone and anti-müllerian hormone ( AMH ). Disruption of typical development may result in the development of both, or neither, duct system, which may produce morphologically intersex individuals. Males : The SRY gene when transcribed and processed produces SRY protein that binds to DNA and directs the development of the gonad into testes. Male development can only occur when the fetal testis secretes key hormones at a critical period in early gestation. The testes begin to secrete three hormones that influence the male internal and external genitalia : they secrete anti-müllerian hormone ( AMH ), testosterone, and dihydrotestosterone ( DHT ). Anti-müllerian hormone causes the paramesonephric ducts to regress. Testosterone converts the mesonephric ducts into male accessory structures, including the epididymis, vas deferens, and seminal vesicle. Testosterone will also control the descending of the testes from the abdomen into the scrotum. Many other genes found on other autosomes, includingWT - 1, SOX9, SF - 1 also play a role in gonadal development. Females : Without testosterone and AMH, the mesonephric ducts degenerate and disappear. The paramesonephric ducts develop into a uterus, fallopian tubes, and upper vagina. There still remains a broad lack of information about the genetic controls of female development, and much remains unknown about the female embryonic process. External genital differentiation Photograph of an adult female human and an adult male. Note that both models have partially shaved body hair. Males become externally distinct between 8 and 12 weeks, as androgens enlarge the phallus and cause the urogenital groove and sinus to fuse in the midline, producing an unambiguous penis with a phallic urethra, and a thinned, rugated scrotum. Dihydrotestosterone will differentiate the remaining male characteristics of the external genitalia. A sufficient amount of any androgen can cause external masculinization. The most potent is dihydrotestosterone ( DHT ), generated from testosterone in skin and genital tissue by the action of 5α - reductase. A male fetus may be incompletely masculinized if this enzyme is deficient. In some diseases and circumstances, other androgens may be present in high enough concentrations to cause partial or ( rarely ) complete masculinization of the external genitalia of a genetically female fetus. The testes begin to secrete three hormones that influence the male internal and external genitalia. They secrete anti-müllerian hormone, testosterone, and Dihydrotestosterone. anti-Müllerian hormone ( AMH ) causes the paramesonephric ducts to regress. Testosterone, which is secreted and converts the mesonephric ducts into male accessory structures, such as epididymis, vas deferens and seminal vesicle. Testosterone will also control the descending of the testes from the abdomen into the scrotom. Dihydrotestosterone, also known as ( DHT ) will differentiate the remaining male characteristics of the external genitalia. Further sex differentiation of the external genitalia occurs at puberty, when androgen levels again become disparate. Male levels of testosterone directly induce growth of the penis, and indirectly ( via DHT ) the prostate. Alfred Jost observed that while testosterone was required for mesonephric duct development, the regression of the paramesonephric duct was due to another substance. This was later determined to be paramesonephric inhibiting substance ( MIS ), a 140 kD dimeric glycoprotein that is produced by sertoli cells. MIS blocks the development of paramesonephric ducts, promoting their regression. Secondary sexual characteristics Breast Visible differentiation occurs at puberty, when estradiol and other hormones cause breasts to develop in typical females. Psychological and behavioral differentiation Human adults and children show many psychological and behavioral sex differences. Some ( e.g., dress ) are learned and obviously cultural. Others are demonstrable across cultures and have both biological and learned determinants. For example, some studies claim girls are, on average, more verbally fluent than boys, but boys are, on average, better at spatial calculation. Some have observed that this may be due to two different patterns in parental communication with infants, noting that parents are more likely to talk to girls and more likely to engage in physical play with boys. Because people can not explore hormonal influences on human behavior experimentally, the relative contributions of biological factors and learning to human psychological and behavioral sex differences ( especially gender identity, role, and sexual orientation ) are controversial ( and hotly contested ). Current theories on mechanisms of sexual differentiation of brains and behavior in humans are based primarily on three sources of evidence : animal research involving manipulation of hormones in early life, observation of outcomes of small numbers of individuals with intersex conditions or cases of early sex reassignment, and statistical distribution of traits in populations ( e.g., rates of homosexuality in twins ). Many of these cases suggest some genetic or hormonal effect on sex differentiation of behavior and mental traits this has been disputed as poor interpretation of scientific methodology. Intersex conditions Main article : Intersex The following are some of the variations associated with atypical determination and differentiation process : A zygote with only X chromosome ( XO ) results in Turner syndrome and will develop with female characteristics. Congenital adrenal hyperplasia - Inability of adrenal to produce sufficient cortisol, leading to increased production of testosterone resulting in severe masculinization of 46 XX females. Persistent müllerian duct syndrome - A rare type of pseudohermaphroditism that occurs in 46 XY males, caused by either a mutation in the Müllerian inhibiting substance ( MIS ) gene, on 19p13, or its type II receptor, 12q13. Results in a retention of Müllerian ducts ( persistence of rudimentary uterus and fallopian tubes in otherwise normally virilized males ), unilateral or bilateral undescended testes and sometimes causes infertility. XY differences of sex development - Atypical androgen production or inadequate androgen response, which can cause incomplete masculinization in XY males. Varies from mild failure of masculinization with undescended testes to complete sex reversal and female phenotype ( Androgen insensitivity syndrome ) Swyer syndrome. A form of complete gonadal dysgenesis, mostly due to mutations in the first step of sex determination ; the SRY genes. A 5 - alpha - reductase deficiency results in atypical development characterized by female phenotype or undervirilized male phenotype with development of the epididymis, vas deferens, seminal vesicle, and ejaculatory duct, but also a pseudovagina. This is because testosterone is converted to the more potent DHT by 5 - alpha reductase. DHT is necessary to exert androgenic effects farther from the site of testosterone production, where the concentrations of testosterone are too low to have any potency. Timeline Human prenatal sexual differentiation Fetal age ( weeks ) Crown - rump length ( mm ) Sex differentiating events blastocyst Inactivation of one X chromosome 2 - 3 Development of wolffian ducts 5 7 Migration of primordial germ cells in the undifferentiated gonad 6 10 - 15 Development of müllerian ducts 7 13 - 20 Differentiation of seminiferous tubules 8 30 Regression of müllerian ducts in male fetus 8 32 - 35 Appearance of Leydig cells. First synthesis of testosterone 9 43 Total regression of müllerian ducts. Loss of sensitivity of müllerian ducts in the female fetus 9 43 First meiotic prophase in oogonia 10 43 - 45 Beginning of masculinization of external genitalia 10 50 Beginning of regression of wolffian ducts in the female fetus 12 70 Fetal testis is in the internal inguinal ring 12 - 14 70 - 90 Male penile urethra is completed 14 90 Appearance of first spermatogonia 16 100 Appearance of first ovarian follicles 17 120 Numerous Leydig cells. Peak of testosterone secretion 20 150 Regression of Leydig cells. Diminished testosterone secretion 24 200 First multilayered ovarian follicles. Canalisation of the vagina 28 230 Cessation of oogonia multiplication 28 230 Descent of testis See also Heteronormativity Gender essentialism Neuroscience of sex differences Sex differences in humans Further reading Josso, Nathalie. ( May 10, 2008 ). Sex Determination. Differences of Sex Determination. June 26, 2012. De Felici, M. ( 2010 ). `` Germ stem cells in the mammalian adult ovary : Considerations by a fan of the primordial germ cells ''. Molecular Human Reproduction. 16 ( 9 ) : 632 -- 6. doi : 10.1093 / molehr / gaq006. PMID 20086005. Rodolfo Rey. ( November 10, 2009 ). Externalgenitalia. Endotext. June 26, 2012. Sharman, GB ; Hughes, RL ; Cooper, DW ( 1989 ). `` The Chromosomal Basis of Sex - Differentiation in Marsupials ''. Australian Journal of Zoology. 37 ( 3 ) : 451. doi : 10.1071 / ZO9890451. Watson, CM ; Margan, SH ; Johnston, PG ( 1998 ). `` Sex - chromosome elimination in the bandicoot Isoodon macrourus using Y - linked markers ''. Cytogenetics and Cell Genetics. 81 ( 1 ) : 54 -- 9. doi : 10.1159 / 000015008. PMID 9691176. Minireview : Sex Differentiation. References ^ Jump up to : Hughes, Ieuan A. ( 1 August 2001 ). `` Minireview : Sex Differentiation ''. Endocrinology. 142 ( 8 ) : 3281 -- 3287. doi : 10.1210 / endo. 142.8. 8406. Retrieved 2 October 2017 -- via endo.endojournals.org. Jump up ^ `` Human sexual differentiation ''. Gfmer.ch. Retrieved 2 October 2017. Jump up ^ Mukherjee, Asit B. ; Parsa, Nasser Z. ( 1990 ). `` Determination of sex chromosomal constitution and chromosomal origin of drumsticks, drumstick - like structures, and other nuclear bodies in human blood cells at interphase by fluorescence in situ hybridization ''. Chromosoma. 99 ( 6 ) : 432 -- 5. doi : 10.1007 / BF01726695. PMID 2176962. 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Harrison 's principles of internal medicine ( 17th ed. ). New York : McGraw - Hill Medical. pp. 2339 -- 2346. ISBN 978 - 0 - 07 - 147693 - 5. ^ Jump up to : Fausto - Sterling, Anne ( 1992 ). Myths of Gender, Revised Edition. Perseus Books ( HarperCollins ), 81 - 82. Jump up ^ Hughes, Ieuan A... ( June 12, 2011 ). Jump up ^ Jost, A. ; Price, D. ; Edwards, R.G. ( 1970 ). `` Hormonal Factors in the Sex Differentiation of the Mammalian Foetus ( and Discussion ) ''. Philosophical Transactions of the Royal Society B : Biological Sciences. 259 ( 828 ) : 119 -- 31. Bibcode : 1970RSPTB. 259... 119J. doi : 10.1098 / rstb. 1970.0052. JSTOR 2417046. Jump up ^ Halpern, Diane F. ( 2011 ). Sex Differences in Cognitive Abilities : 4th Edition. NY : Psychology Press. Jump up ^ Geary, David C. ( 2009 ). Male, Female : The Evolution of Human Sex Differences ( 2nd Ed. ) Washington, D.C. : American Psychological Association. ^ Jump up to : 1963 -, Jordan - Young, Rebecca M.,. Brain storm : the flaws in the science of sex differences ( First Harvard University Press paperback ed. ). Cambridge, Massachusetts. ISBN 9780674063518. OCLC 733913684. ^ Jump up to : Cordelia., Fine, ( 2011 ). Delusions of Gender : The Real Science Behind Sex Differences. London : Icon Books. ISBN 9781848312203. OCLC 707442506. Jump up ^ Pinker, Steven ( 2002 ). The Blank Slate. New York : Penguin. pp. 346 -- 350. Jump up ^ MacLaughlin, David T. ; Donahoe, Patricia K. ( 2004 ). `` Sex Determination and Differentiation ''. New England Journal of Medicine. 350 ( 4 ) : 367 -- 78. doi : 10.1056 / NEJMra022784. PMID 14736929. Jump up ^ PC Sizonenko in Pediatric Endocrinology, edited by J. Bertrand, R. Rappaport, and PC Sizonenko, ( Baltimore : Williams & Wilkins, 1993 ), pp. 88 -- 99 Jump up ^ `` Page Not Found - HHMI BioInteractive '' ( PDF ). Hhmi.org. Retrieved 2 October 2017. Sources Achermann, John ; Jameson, Larry ( 2012 ). Fauci, Anthony S., ed. 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Sex differences in humans Physiology Medicine Sexual differentiation Autism Narcissism Schizophrenia Stroke care Neuroscience Memory Eyewitness memory Cognition Intelligence Emotional intelligence Psychology Gender psychology Sociology Crime Education Leadership Social capital Suicide Sex determination and differentiation Overview Sexual differentiation humans Development of the reproductive system gonads Mesonephric duct Paramesonephric duct Genetic basis Sex - determination system XY X0 ZW Temperature - dependent Haplodiploidy Sex chromosome X chromosome Y chromosome Testis - determining factor See also Hermaphrodite Intersex Disorders of sex development Development of the reproductive system Precursors Mesoderm intermediate lateral plate Endoderm Cloaca Urogenital sinus Ectoderm Cloacal membrane Internal Development of the gonads Gonadal ridge Pronephric duct Mesonephric duct Paramesonephric duct Vaginal plate Definitive urogenital sinus External Genital tubercle Labioscrotal swelling Primordial phallus Gubernaculum Peritoneum Vaginal process Canal of Nuck See also List of related male and female reproductive organs Prenatal development Embryogenesis Sex Biological terms Sexual dimorphism Male Female Sexual differentiation Feminization Virilization Sex - determination system XY ZW XO ZO Temperature - dependent Haplodiploidy Heterogametic sex / Homogametic sex Sex chromosome X chromosome Y chromosome Testis - determining factor Hermaphrodite Sequential hermaphroditism Intersex parasexuality Sexual reproduction Evolution of sexual reproduction Anisogamy Isogamy Germ cell Reproductive system Sex organ Meiosis Gametogenesis Spermatogenesis Oogenesis Gamete spermatozoon ovum Fertilization External Internal Sexual selection Plant reproduction Fungal reproduction Sexual reproduction in animals Sexual intercourse Copulation Human reproduction Sexuality Plant sexuality Animal sexuality Human sexuality Mechanics Differentiation Activity Sex portal Biology portal Human physiology of sexual reproduction Menstrual cycle Menarche Menstruation Follicular phase Ovulation Luteal phase Gametogenesis Spermatogenesis spermatogonium spermatocyte spermatid sperm ) Oogenesis ( oogonium oocyte ootid ovum ) Germ cell gonocyte gamete ) Human sexual activity Sexual arousal Sexual intercourse Masturbation Erection Orgasm Ejaculation Insemination Fertilization / Fertility Implantation Pregnancy Postpartum period Mechanics of sex Development of the reproductive system Sexual differentiation Sexual dimorphism Feminization Virilization ) Puberty Gonadarche Tanner scale Pubarche Menarche Spermarche Adrenarche ) Maternal age / Paternal age Menopause Egg Ovum Oviposition Oviparity Ovoviviparity Vivipary Reproductive endocrinology and infertility Hypothalamic -- pituitary -- gonadal axis Hypothalamic -- pituitary -- prolactin axis Andrology Hormone Breast Thelarche Development Lactation Breastfeeding Human reproductive system Male Female Retrieved from `` https://en.wikipedia.org/w/index.php?title=Sexual_differentiation_in_humans&oldid=858369950 '' Categories : Sex - determination systems Epigenetics Human reproduction Physiology Hidden categories : CS1 maint : Archived copy as title Talk Contents About Wikipedia Русский Tagalog Tiếng Việt 中文 Edit links This page was last edited on 6 September 2018, at 17 : 48 ( UTC ). 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Question: when do you become genetically male or female
Answer: at the time of fertilization