determination of biological sex 314

• reproductive system consists of

  primary and secondary sex organs
• primary sex organs (gonads)

  produce gametes (testes or ovaries)
• secondary sex organs


  organs other than gonads that are necessary for reproduction

  -male: system of ducts, glands; penis delivers sperm cells

  -female: uterine tubes, uterus, and vagina receive sperm and harbor developing fetus
• external genitalia


  located in perineum

  -externally visible (except accessory glands of female perineum)
• internal genitalia


  located in pelvic cavity

  -except testes and some associated ducts in scrotum
• secondary sex characteristics


  features that distinguish sexes and influence mate attraction

  -develop at puberty
• secondary sex characteristics in both sexes


  pubic and axillary hair and their associated scent glands, and pitch of voice
• secondary sex characteristics in males


  facial hair, coarse and visible hair on torso and limbs, muscle development
• secondary sex characteristics in females


  distribution of body fat, mammary gland development, and less body hair production
• male and female gametes (sex cells) combine their genes to form a


  zygote (fertilized egg)

  -one gamete has motility: sperm (spermatozoon)

  -other gamete contains nutrients for developing embryo: egg (ovum)
• sperm (spermatozoon)


  -parent producing sperm considered male

  -parent with a Y chromosome is male (needs to contain an SRY region)
• egg (ovum)


  -for sake of reproduction, parent producing eggs considered female

  -in mammals, female in parent that provides a sheltered internal environment and prenatal nutrition of embryo
• male reproductive system serves to


  produce sperm and introduce them into female body

  -males external genitalia serves to transfer gametes to female reproductive tract
• female reproductive system functions


  produces eggs, receives sperm, provides for gametes' union, harbors fetus, and nourishes offspring

  -females have a copulatory organ (vagina) for accepting genetic information (sperm)
• Y chromosomes have sex determining region (SRY)


  determine male phenotype

  -other Y chromosomal genes are needed for male to thrive
• XX with SRY region


  sterile males with effeminate appearance
• XXY / XXXY

  klinefelter syndrome

  -1 in 800 births

  -sterile male with effeminate appearance

  -cognitively average with XXY, delayed with XXXY
• XXX

  triple X syndrome

  -1 in 1000 births

  -fertile female with "older" appearance

  -physically larger, cognitively average
• XYY

  jacob's syndrome

  -1 in 1000 births

  -sterile male, physically taller than average

  -cognitive average
• XY

  androgen insensitivity

  -1 in 20,000 births

  -male chromosomes that have SRY region, but lacks ability to respond to male sex hormones

  -partial (hermaphrodite) or complete
• initially, a fetus is _____

  sexually undifferentiated
• gonads begin to develop at

  5 or 6 weeks as gonadal ridges
• 2 sets of ducts adjacent to each gonadal ridge

  -in males, mesonephric ducts develop into reproductive tract; paramesonephric ducts degenerate

  -in females, paramesonephric ducts develop into reproductive tract; mesonephric ducts degenerate
• SRY gene (sex-determining region of Y chromosome) found only in males


  -SRY codes for a protein, testes-determining factor (TDF), that initiates development of testes

  -testes begin to secrete testosterone at 8 to 9 weeks: stimulates mesonephric ducts to develop into male tracts

  -at same time, testes secrete mullerian-inhibiting factor causing degeneration of paramesonephric ducts
• estrogen levels are always high in pregnancy


  if estrogen was hormone that directed female development, all fetuses would be feminized from mothers hormone
• female development of a fetus occurs whenever there is an ____ of androgen hormones

  absence

  -not because estrogen is present
• two sexes anatomically indistinguishable for first _____ weeks of development

  8 to 10
• female reproductive tract develops from ____

  paramesonephric ducts

  -not because of positive action of any hormone

  -because of absence of testosterone and mullerian-inhibiting factor (MIF)
• similar development of external genitalia of both sexes


  -genital tubercle becomes head (glans) of penis or glans clitoris

  -pair of urogenital folds encloses male urethra helping to form penis or form labia minora

  -pair of labioscrotal folds becomes either scrotum or labia majora
• by week ____, either male or female genitalia are distinctly formed

  12
• male and female organs that develop from same embryonic structure are homologous

  -penis is homologous to clitoris

  -scrotum is homologous to labia majora