Gametogenesis and Fertilisation

A 28-year-old man attends an infertility clinic with his wife for evaluation of primary infertility (2 years duration). His wife's investigations are normal. Semen analysis reveals: volume 2.2 mL, pH 7.8, sperm concentration 45 million/mL, total sperm count 99 million, motility 35% (normal >40%), and morphology 6% normal forms (normal >4%). Repeat semen analysis 2 weeks later shows: concentration 38 million/mL, motility 28%, morphology 5%. The patient denies fever, genitourinary symptoms, or recent illness. Testicular examination is normal with normal testicular volume bilaterally. Serum testosterone is 450 ng/dL (normal 300–1000), FSH is 8.2 mIU/mL (normal 1.7–8.8), and LH is 7.1 mIU/mL (normal 1.7–8.6). What is the most likely explanation for this patient's semen abnormality based on the gametogenesis process?

During spermatogenesis, which phase of meiosis I is characterized by the pairing of homologous chromosomes and formation of tetrads?

At what stage of oogenesis is the first polar body extruded, and what is the ploidy of the secondary oocyte at this point?