WBR0338

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Reproductive
Prompt	[[Prompt::A researcher studying the process of ovulation in human females recruits 10 female volunteers. He injects subcutaneously human chorionic gonadotropin (HCG) hormone and retrieves the eggs 35 hours later. Using the appropriate technique, he views the eggs under fluorescence microscopy. Under fluorescence microscopy, which of the following observations does the researcher most likely make?]]
Answer A	AnswerA::Beginning of the disappearance of the nuclear envelope
Answer A Explanation	AnswerAExp::Early prophase I is characterized by the disappearance of the nuclear envelope.
Answer B	AnswerB::Alignment of the sister chromatids on the equatorial plate.
Answer B Explanation	AnswerBExp::Alignment of the sister chromatids on the equatorial plate occurs during metaphase II, the step where oocyte arrest takes place, following ovulation and before fertilization.
Answer C	AnswerC::Alignment of the homologous chromosomes on the equatorial plate
Answer C Explanation	AnswerCExp::Alignment of the homologous chromosomes on the equatorial plate occurs during metaphase I.
Answer D	AnswerD::Movement of sister chromatids to opposite poles
Answer D Explanation	AnswerDExp::Movement of sister chromatids to opposite poles occurs during anaphase II.
Answer E	AnswerE::Movement of homologous chromosomes to opposite poles
Answer E Explanation	AnswerEExp::Movement of homologous chromosomes to opposite poles occurs during anaphase I.
Right Answer	RightAnswer::B
Explanation	[[Explanation::The process described above is induction of ovulation, whereby patients typically receive subcutaneous injections of HCG (a mimicker of LH) followed by egg retrieval 35-40 hours later. In this process, ovulation is most likely occurs and retrieval of oocytes is then made possible. Typically in females, following ovulation, oocytes are arrested at metaphase II, before fertilization takes place. Only if fertilization occurs, will the oocyte presume meiosis II. Under fluorescence microscopy, metaphase II is characterized by the presence of sister chromatids along the equatorial plate. In contrast, metaphase I is characterized by the presence of homologous chromosomes along the equatorial plate. Different species produce oocytes at different stages of meiosis. Educational Objective: Meiosis of human oocytes is arrested at metaphase II following ovulation. Metaphase II is characterized by the presence of sister chromatids along the equatorial plate. References: First Aid 2014 page 569]]
Approved	Approved::Yes
Keyword	WBRKeyword::metaphase I, WBRKeyword::metaphase II, WBRKeyword::anaphase, WBRKeyword::prophase, WBRKeyword::telophase, WBRKeyword::meiosis, WBRKeyword::oocyte, WBRKeyword::egg, WBRKeyword::HCG, WBRKeyword::human, WBRKeyword::chorionic gonadotropin, WBRKeyword::ovulation, WBRKeyword::fertilization, WBRKeyword::fluorescence microscopy
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Order in Linked Questions	LinkedOrder::