Reproduction 1

• Chromosomal sex


  Autosomal chromosomes + a pair of sex chromosomes

  
• Sex-determining region Y (SRY) gene


  • Necessary for the development of the testes, testicular hormones and male characteristics

  
• Gonads are composed of 3 cell types

  • Supporting cells (Sertoli or granulosa cells)
  • Stromal cells (Leydig or theca cells)
  • Germ cells (spermatogonia or oocytes)
• Anti-mullerian hormone


  Hormone secreted by foetal testes essential for development of the male gonads and internal genitalia
• Testosterone


  Hormone secreted by foetal testes essential for development of the male gonads and internal genitalia
• Dihydrotestosterone


  Responsible for development of male external genitalia
• Indifferent gonads


  The early genital system is similar in both sexes - primordia of the gonads

  
• Gonadal differentiation

  1. Depends on whether Y chromosome is present

  2. Development of the gonads: Testes & ovaries

  3. Development of the genital ducts and auxiliary genital glands

  4. Development of the external genitalia

  
• Mullerian inhibiting hormone (MIH)


  Secreted by Sertoli cells, causes local, ipsilateral regression of the Mullerian duct
• Testosterone


  Secreted by Leydig cells, causes local, ipsilateral development of the Wolffian ducts
• Psychic sex


  • Certain regions of the brain are sexually dimorphic and differentially sensitive to steroids
  • Preoptic area and ventromedial nucleus of the hypothalamus
  • Amygdala

  
• Testosterone


  Presence or absence during foetal development (humans) or soon after birth in some species (rodents) responsible for neurological alterations which affect sex differences in thinking, sexual orientation, aggression and cognitive functioning
• Estrogens


  Derived from the neural aromatization of testosterone, cause the brain to develop as male in their presence and as female in their absence
• Alpha-fetoprotein


  Plasma glycoprotein that binds estrogen and acts as a carrier, protecting the foetal brain from the masculinizing effect of estrogen by preventing its entry into cells
• Turner's syndrome is a disorder of chromosomal sex where the karyotype is XO, the gonads contain rudimentary ovarian tissue, and the phenotype is female with no maturation at puberty

  
• Klinefelter's syndrome is a disorder of chromosomal sex where the karyotype is XXY, there is testicular development but the seminiferous tubules are abnormal and there is no spermatogenesis

  
• Super female/Trisomy X is a disorder of chromosomal sex where the karyotype is XXX and there are ovary abnormalities

  
• True hermaphroditism


  Rare disorder where there is presence of testicular tissue (with distinct seminiferous tubules) and ovarian tissue (with mature Graafian follicles) in a single individual, common karyotype is XX, internal genitalia correspond to the 'sex' of the ipsilateral gonad, external genitalia are ambiguous

  
• Causes of true hermaphroditism include division of one ovum followed by fertilization of each haploid ovum and fusion of the two zygotes early in development, an ovum fertilized by two sperms followed by trisomic rescue, and two ova fertilized by two sperm cells fusing to form a tetragametic chimera
• Male pseudohermaphroditism


  Disorder where the karyotype is XY, the internal genitalia are male (testes), but the external genitalia resemble a female and are ambiguous, caused by abnormalities of Leydig cell function or androgen insensitivity

  
• Female pseudohermaphroditism

  Disorder where the karyotype is XX, the internal genitalia are female (ovaries), but the external genitalia are partially masculinized and ambiguous, caused by congenital adrenal hyperplasia or placental aromatase deficiency
• Common karyotypes and associated gonad status and genitalia in disorders of phenotypic sex

  • True hermaphrodite: XX, ovary and testes or ovotestis, hypospadia, variable/rudimentary uterus
  • Male hermaphrodite: XY, testes, hypospadia/micropenis, absent uterus
  • Female hermaphrodite: XX, ovary, hypospadia, present uterus

  
• Freemartinism

  An infertile female cattle with masculinized behaviour and non-functioning ovaries born twin to a male, where the female (XX) acquires the male (XY) component in utero by exchange of some cellular material from a male twin, via vascular connections between placentas