Final answer:
XY mice with a conditional Cre knockout of Sox9 in the bipotential gonad are expected to display a female phenotype, as Sox9 is crucial for the development of male-specific organs, and its absence would lead to the default pathway of ovarian development. The correct option is b.
Step-by-step explanation:
In the context of embryonic development, the SRY gene plays a critical role in determining male sex characteristics by setting in motion the development of testes from the bipotential gonad. The Sox9 gene is also essential in this process, as it is one of the genes recruited by SRY to promote testis development. However, when Sox9 is knocked out in the bipotential gonad of an XY mouse using a Sf-1cre, this would disrupt the usual development pathway, as the activation sequence that leads to the differentiation of spermatogonia and subsequent male phenotype would be affected.
Given this information, the conditional Cre knockout of Sox9 would eliminate its function in the cascade of gene expression that typically leads to the development of male-specific organs. Consequently, without Sox9, the differentiation of the bipotential gonad towards testes formation could be severely compromised, and the embryonic gonadal development could default to forming an ovary, as would typically occur in the absence of SRY activity, leading to a phenotypic outcome consistent with the female sex.
Therefore, one would expect XY mice with a conditional Cre knockout of Sox9 to display a female phenotype, as the normal male developmental pathway cannot proceed without the essential function of Sox9 in the gonadal differentiation process. Hence, the correct answer to the student's question would be option (b. Female).