Question at position 16 The development of male gonads (testes) is initiated bymultiple genes on the long arm of the Y chromosomeestrogenpubertythe SRY geneClear my selectionSingle choice
A
multiple genes on the long arm of the Y chromosome
B
estrogen
C
puberty
D
the SRY gene

Question

Question at position 16 The development of male gonads (testes) is initiated bymultiple genes on the long arm of the Y chromosomeestrogenpubertythe SRY geneClear my selection

BlackTom AI · Accepted Answer

The SRY gene on the Y chromosome encodes the testis-determining factor that initiates male gonadal development.

1. Relevant knowledge points and concepts
- Genetic sex in mammals is typically determined by sex chromosomes: XX = genetic female, XY = genetic male.
- The SRY (Sex-determining Region Y) gene, located on the short arm of the Y chromosome, is the pivotal switch that drives indifferent (bipotential) gonadal primordia to differentiate into testes.
- Sertoli cell differentiation and secretion of anti-Müllerian hormone (AMH) and Leydig cell production of testosterone are downstream events that produce male internal and external reproductive structures.

2. Step-by-step reasoning process
1) An embryo with an XY karyotype carries the SRY gene. 
2) SRY expression in the genital ridge upregulates testis-promoting genes (notably SOX9). 
3) SOX9 and other factors drive differentiation of supporting cells into Sertoli cells. 
4) Sertoli cells secrete AMH → regression of Müllerian (female) ducts. 
5) Leydig cells, induced in testicular development, secrete testosterone → maintenance and differentiation of Wolffian ducts into epididymis, vas deferens, seminal vesicles. Dihydrotestosterone (DHT) drives masculinization of external genitalia.

3. Intermediate steps and molecular links
- SRY → transcriptional activation of SOX9 → Sertoli cell fate.
- Sertoli cells → AMH → Müllerian duct regression.
- Leydig cells → testosterone → Wolffian duct development; testosterone → DHT → external genitalia.

4. Why the correct answer is correct
SRY is the primary genetic trigger that converts the bipotential gonad into a testis. Without SRY (or functional downstream pathway), testes do not form even if a Y chromosome is present.

5. Why other options are incorrect
- "Multiple genes on the long arm of the Y chromosome": Incorrect because the key determinant is SRY (on the short arm), not multiple long-arm genes.  
- "Estrogen": Incorrect; estrogen is associated with female differentiation and does not initiate testis development.  
- "Puberty": Incorrect; puberty is a later physiological maturation stage that follows gonadal differentiation, not the initiating cause of testis development.

6. Conclusion
The SRY gene is the correct initiator of male gonad (testis) development, confirming the provided answer: the SRY gene.

Question at position 16 The development of male gonads (testes) is initiated bymultiple genes on the long arm of the Y chromosomeestrogenpubertythe SRY geneClear my selectionSingle choice

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