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Sex determined in human beings

  1. Determination of sex in human beings is done by their sex chromosomes.
  2. Females have XX chromosomes in their somatic cells whereas, males have XY chromosomes.
  3. Development of functional testes is present in males.
  4. These testes are induced by the activity of TDF (Testes Determining Factor).
  5. TDF is encoded by SRY (Sex Determining Region) that is located on the short arm of Y chromosome.
  6. This SRY is the only gene present at Y chromosome, which is necessary to initiate development of testes and expressed only in the cells that develop gonad.
  7. Expression of these genes in somatic cells differentiates the cells itself into “sertoli cells”.
  8. Sertoli cells are the supporting cells in testes that produce “anti-mullerian hormone”.
  9. This hormone suppresses the development of female reproductive organs.
  10. Sertoli cells also induce the development of “Leydig cells” from somatic cells that secrete the male sex hormone “Testosterone”.
  11. Now, in the absence of SRY gene, the somatic cells that develop gonad develop into “Ovary” and the supporting cells become “follicle cells”.
  12. The other somatic cells become “Theca cells” and secrete the female sex hormone “estrogen”.
  13. The male sex hormone is responsible to induce male secondary sexual characteristics.
  14. The below chart is the summary of the sequences involved in the human sex determination:

Sequences involved in the human sex determination