Gonads do not acquire male or female characteristics until
**Core Concept**
The development of gonadal sex characteristics is a complex process that involves the interplay of genetic, hormonal, and environmental factors. Specifically, the gonads of an embryo must undergo a series of molecular and cellular changes to acquire either male or female characteristics.
**Why the Correct Answer is Right**
During embryonic development, the gonads initially form as indifferent gonads, which are capable of developing into either ovaries or testes. This stage is influenced by the presence or absence of the SRY (sex-determining region Y) gene on the Y chromosome, which triggers the development of testes. The testes then produce anti-Müllerian hormone (AMH), which suppresses the development of female reproductive structures, and Müllerian inhibiting substance (MIS), which causes the regression of the paramesonephric ducts. In contrast, the absence of SRY and the presence of the Wnt4 gene promote the development of ovaries. The gonads do not acquire definitive male or female characteristics until after the 6th week of gestation, when the testes begin to produce testosterone and dihydrotestosterone (DHT), which induce the development of male internal and external genitalia.
**Why Each Wrong Option is Incorrect**
**Option A:** This is not a correct answer, as the indifferent gonads begin to develop into either ovaries or testes much earlier than this.
**Option B:** This option is incorrect, as the gonads undergo significant changes in sex determination much earlier in embryonic development.
**Option C:** This is not a correct answer, as the gonads do not acquire definitive male or female characteristics until after the 6th week of gestation.
**Clinical Pearl / High-Yield Fact**
The SRY gene is a critical regulator of sex determination, and mutations in this gene can lead to sex reversal or other disorders of sex development.
**Correct Answer: C.**