[5][6] The gonads develop from three sources; the mesothelium, underlying mesenchyme and the primordial germ cells.

In the absence of the SRY gene from the Y chromosome, usually the female sex (ovaries instead of testes) will develop.

[9] This decline is likely due, in part, to reduced expression of genes that encode proteins necessary for DNA repair and meiosis.

[10][11] Such reduced expression can lead to increased DNA damage and errors in meiotic recombination.

[9] The testes of older men often have sperm abnormalities that can ultimately lead to male infertility.