Sex Development

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•  A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone

Humans have 46 chromosomes in all diploid somatic cells – 22 pairs are autosomes and the 23rd pair are the sex chromosomes

  • Females possess two copies of the X chromosome (XX), while males possess one X and a shorter Y chromosome (XY)

The Y chromosome includes a gene called the SRY gene (Sex Determining Region Y), which leads to male development

  • The SRY gene codes for a testis-determining factor (TDF) that causes embryonic gonads to form into testes (male gonads)
  • In the absence of the TDF protein (i.e. no Y chromosome), the embryonic gonads will develop into ovaries (female gonads)

The male and female gametes produce different hormones to promote further development of sex characteristics:

  • The testes produce testosterone to promote the further development of male sex characteristics 
  • The ovaries will produce estrogen and progesterone to promote the development of female sex characteristics

Sex Determination in Humans

sex determination

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•  Testosterone causes pre-natal development of male genitalia and both sperm production and development of

    male secondary sexual characteristics during puberty

The main male reproductive hormone is testosterone, which is secreted by the testes and serves a number of roles:

  • It is responsible for the pre-natal development of male genitalia
  • It is involved in sperm production following the onset of puberty
  • It aids in the development of secondary sex characteristics (including body hair, muscle mass, deepening of voice, etc.)
  • It helps to maintain the male sex drive (libido)

The Role of Testosterone in Male Sex Development

male sex development


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•  Estrogen and progesterone cause pre-natal development of female reproductive organs and female secondary

    sexual characteristics during puberty

The main female reproductive hormones (secreted by the ovaries) are estrogen and progesterone, which serve several roles:

  • They promote the pre-natal development of the female reproductive organs
  • They are responsible for the development of secondary sex characteristics (including body hair and breast development)
  • They are involved in monthly preparation of egg release following puberty (via the menstrual cycle)

Initially, estrogen and progesterone are secreted by the mother’s ovaries and then the placenta – until female reproductive organs develop (this occurs in the absence of testosterone)

The Role of Estrogen and Progesterone in Female Sex Development

female sex development