11. Meiosis is used to generate gametes. When is meiosis completed in mammalian
females?
a. During oogonia maturation in the fetal ovaries
b. In all primary oocytes during maturation at puberty
c. In an individual oocyte during the female ovarian cycle
d. During fertilization
Meiosis Completion in Mammalian Females: CSIR NET Life Sciences Solved Question
Meiosis in mammalian females generates gametes through oogenesis, starting in fetal ovaries but completing in stages during the ovarian cycle and fertilization. The correct answer is c. In an individual oocyte during the female ovarian cycle.
Option Analysis
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a. During oogonia maturation in the fetal ovaries: Oogonia are diploid mitotic cells that multiply before entering meiosis; primary oocytes begin meiosis I in the fetus but arrest in prophase I (dictyate stage), never completing it here.
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b. In all primary oocytes during maturation at puberty: Primary oocytes remain arrested from fetal life through puberty; not all resume meiosis simultaneously, only one per cycle under hormonal signals.
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c. In an individual oocyte during the female ovarian cycle: Correct—meiosis I completes in the dominant follicle just before ovulation (luteinizing hormone surge triggers progression to metaphase II arrest), while meiosis II finishes post-fertilization.
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d. During fertilization: Fertilization triggers meiosis II completion (extrusion of second polar body), but meiosis I ends earlier in the ovarian cycle.
Meiosis completed in mammalian females ensures haploid gametes for reproduction, a key process in oogenesis vital for CSIR NET Life Sciences. In fetal ovaries, oogonia enter meiosis I to form primary oocytes arrested at dictyate prophase until puberty.
Oogenesis Timeline
Primary oocytes resume meiosis in the ovarian cycle:
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LH surge in the Graafian follicle completes meiosis I, yielding secondary oocyte and first polar body.
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Secondary oocyte arrests at metaphase II until fertilization triggers meiosis II.
This staggered meiosis reduces aneuploidy risk and conserves resources, unlike continuous spermatogenesis.
Exam Relevance
For CSIR NET, note female meiosis differs from males: fetal initiation, cyclic completion per ovum. Misconceptions like fetal or puberty-wide completion test prophase arrest knowledge.
