#1 - BE: Differentiation Some history: some...

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BE: Differentiation SUMMER 2007 Some history: some “landmarks” I. Earliest hypotheses Aristotle’s theory: Male semen is the primary determinants of the form of the embryo while females provide the material and supportive environment for embryonic development; if semen gain control, males develop; otherwise, embryos become females. Males are “hotter’ than females. Support: no good experimental evidence Arnold Berthold (1849) removed testes of a rooster: stopped crowing, no more aggressive behavior, no more sexual behavior. He reimplanted one testis in body cavity and restored normal crowing, sexual behavior, and aggression. The reimplanted testis had no nerve connections; must have been a chemical released into the circulatory system that changed behavior II. 20 th century hypotheses Geddes & Thompson (1901): the female is the outcome of anabolism and the male the result of katabolism where anabolism = endothermic and katabolism = exothermic contributors (not supported) Stevens (1905): sex is determined by chromosome pairs. Supported in mealworm research. Eggs supported by small chromosomes became male; those fertilized by chromosomes of equal size became female Lillie (1916): the freemartin effect in cattle (which occurs when a female in the womb becomes sterile due to androgens associated with her male co-twin) gave rise to the suspicion that hormone levels (and not just genotypes) were involved in differentiation of the sexes: testicular secretions induced masculine characteristics and ovarian secretions induced feminine attributes Pfeiffer (1936): hypothesized that perinatal (“around the time of birth”) testicular secretions have a permanent effect on some pituitary functions in adult rats. Manipulations and results: 1. newborn females + testes anovulatory ovaries, lack of corpora lutea 2. castrated adult females + ocular ovarian implants follicles, corpora lutea and vaginal cyclicity 3. castrated males + ocular ovarian implants follicles only Support for “masculinization” of the adenohypophysis (anterior pituitary) with the hypophysis as “bipotential” depending on whether an ovary or testis is present (= dominant model of the period) 1
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[Recall the ovarian cycle: follicular phase (oocyte is nurtured by the follicles); periovulatory phase (follicles rupture and release the oocyte) and luteal phase (remaining follicle becomes the corpus luteum) Be sure to review the Animated tutorial The Ovarian and Uterine Cycles ] 1940s “literature gap”: a period of quiescence until the “hypothalamus- hypophyseal chemotransmitter hypothesis” was put forward; researchers had to consider the idea that pituitary function was controlled by the brain
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#1 - BE: Differentiation Some history: some...

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