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I can answer this for mammals. The mammalian oocyte (egg) is surrounded by a layer called the zona pellucida. There are three well-characterized proteins in this layer, called ZP1, ZP2 and ZP3 (not very imaginative, I know). I don't know much about ZP1 but ZP2 and ZP3 are involved in fertilization. The sperm's outer surface has receptors for ZP2 and ZP3. ...


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Strictly defined, a hysterectomy is removal of only the uterus. But sometimes the ovaries are also removed, depending on the reason for the surgery and age of the woman. If the ovaries are also removed, there would no ovarian or uterine cycling, true. But without the negative feedback effect of ovarian steroids (progesterone and estrogen), levels of both ...


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Yes, it is perfectly possible for both pairs of non-sister chromatids to cross over in a single tetrad. The "standard textbook" depiction is a simplification, true tetrads can sometimes be very complicated and the nested crossing-over would be difficult for entry-level textbooks to cover. This microscope image clearly shows two chiasmata occurring on two ...



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