Indifferent gonad
In embryonic life, the gonad in males and females is initially identical. This gonad is said to be "indifferent" before it differentiates into a definitive testis or ovary. An indifferent gonad becomes a testis if the embryo has a Y chromosome, but if the embryo has no Y chromosome, the indifferent gonad becomes an ovary. Thus, an XY chromosome complement leads to testes while an XX chromosome complement leads to ovaries. People with just one X chromosome and no Y are females with Turner syndrome, and are infertile. The absence of a Y chromosome permits the indifferent gonad to become an ovary, but both X chromosomes are needed for the ovary to function normally.

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the sexually undifferentiated gonad of the early embryo. In human embryos this stage occurs during the fifth to seventh weeks.

Medical dictionary. 2011.

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