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