This article's factual accuracy is disputed. Relevant discussion may be found on the talk page. Please help to ensure that disputed statements are reliably sourced. When the baby is conceived, a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell, determining whether the baby will be female XX or male XY. It is the Y chromosome that is essential for the development of the male reproductive organs, and with no Y chromosome, an embryo will develop into a female.
This is because of the presence of the sex determining region of the Y chromosome, also known as the SRY gene.
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. 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: 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 cannot be determined because the reproductive structures do not differentiate until the seventh week. Prior to this, the child is considered bipotential because it cannot be identified as male or female.
Internal genital differentiation[ edit ] The internal genitalia consist of two accessory ducts: The mesonephric system is the precursor to the male genitalia and the paramesonephric to the female reproductive system. This depends on the presence or absence of the sex determining region of the Y chromosome, also known as the SRY gene.
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: Disruption of typical development may result in the development of both, or neither, duct system, which may produce morphologically intersex individuals.
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: 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. Without testosterone and AMH, the mesonephric ducts degenerate and disappear.
The paramesonephric ducts develop into a uterus , fallopian tubes , and upper vagina. 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 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. 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.
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 kD dimeric glycoprotein that is produced by sertoli cells. MIS blocks the development of paramesonephric ducts , promoting their regression.
Psychological and behavioral differentiation[ edit ] This section possibly contains original research. Please improve it by verifying the claims made and adding inline citations.
Statements consisting only of original research should be removed. May Learn how and when to remove this template message Human adults and children show many psychological and behavioral sex differences. 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. 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 The following variations are associated with atypical determination and differentiation process: 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.
Human prenatal sexual differentiation  Fetal age.