In the tammar wallaby, which of the following is true about sex determination?

Question

In the tammar wallaby, which of the following is true about sex determination?

BlackTom AI · Accepted Answer

Let's examine each statement in light of sex determination in the tammar wallaby and general mammalian biology.
Option 1: 'SRY expression determines scrotal development' — This aligns with the idea that SRY expression drives testes development, which in turn influences downstream androgen production and male-associated traits. If SRY is expressed, gonads develop as testes, which then produce testosterone and related hormones that influence male differentiation, including scrotal development. Although the direct causal chain to scrotal development can be more complex and involve multiple downstream hormones, this statement captures the key role of SRY in initiating male (testicular) development that ultimately leads to male external genitalia features. Therefore, this option is consistent with known mechanisms and is considered true in the provided context.
Option 2: 'Penis development is regulated by the number of X chromosomes' — This is incorrect. In mammals, penis development is not determined by chromosome count alone; sex differentiation is directed by the presence of the SRY gene on the Y chromosome, which initiates testis formation and subsequent androgen-mediated development. X-number does not deterministically control penile development.
Option 3: 'Dihydrotestosterone can only be made via the classical steroid pathway' — This is inaccurate. DHT can be produced through alternative routes as well, such as conversion from testosterone by 5α-reductase, which is part of the typical pathway but not exclusive to a single “classical” route. The wording here oversimplifies androgen biosynthesis and overstates exclusivity of a single pathway.
Option 4: 'Androgen synthesis requires DHEA and androstendione' — This is misleading. While DHEA and androstenedione are precursors in androgen synthesis, they are not strictly required in all contexts; androgen synthesis can proceed via multiple precursor pools and enzymatic steps depending on species, tissue, and developmental stage. The statement overgeneralizes the precursor requirement.
Option 5: 'Testosterone levels are similar in male and female pouch young' — This is false. In most marsupials, as in other mammals, males develop higher expected testosterone levels due to testicular production, influencing male-specific development. Therefore, they are not typically similar between sexes in pouch young.

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