WBR0338

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
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 appropriate technique, he visualizes 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 is seen in metaphase II, which is the step that oocyte arrest at after ovulation 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 is seen in metaphase I.
Answer D	AnswerD::Movement of sister chromatids to opposite poles
Answer D Explanation	AnswerDExp::Movement of sister chromatids to opposite poles is seen in anaphase II.
Answer E	AnswerE::Movement of homologous chromosomes to opposite poles
Answer E Explanation	AnswerEExp::Movement of homologous chromosomes to opposite poles is seen in anaphase I.
Right Answer	RightAnswer::B
Explanation	[[Explanation::The process described above is induction of ovulation, whereby patients typically receive subcutaneous injections of HCG (mimicker of LH) followed by egg retrieval 35-40 hours later. In this process, ovulation is most likely to have occurred and retrieval of oocytes is then made possible. Normally in a human female, oocytes are arrested after ovulation at metaphase II before fertilization takes place. Only if fertilization ever happens, the oocyte should 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. Remarkably, different species have their oocytes at different stages of meiosis. Educational Objective: Meiosis of human oocytes is arrested at metaphase II after ovulation. Metaphase II is characterized by the presence of sister chromatids along the equatorial plate. References: ]]
Approved	Approved::No
Keyword	WBRKeyword::metaphase, WBRKeyword::I, WBRKeyword::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::fluorescent, WBRKeyword::fluorescence, WBRKeyword::microscope, WBRKeyword::microscopy
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