Sex Differences in Behavior: Sex Determination and Differentiation

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Chapter 3 Sex Differences in Behavior Sex
Determination and Differentiation
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Stereotypes based on trends.
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• Sexual differentiation the developmental
  process leading to becoming a male or a female
• Hormones and environmental experiences guide
  development of physiological, morphological, and
  behavioral characteristics that are displayed
  later in life.
• Sex Determination and Sex Differentiation are
  different, but closely related
• Chromosomal sex (fertilization)
• Gonadal sex (ovaries or testes)
• Gametic sex (which type of gametes are produced)
• Hormonal sex (estrogen to androgen ratio)
• Morphological sex (differences in body type)
• Behavioral sex (male-typical vs female-typical)
• Specifically in humans
• Gender identity (sex or gender a person feels
  themselves to be)
• Sexual orientation (preference for a sex partner)
• Legal sex (governmentally determined)

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3.3 Levels of sex determination
Please notice how the line between chromosomal
sex and morphological sex is a dashed line, not a
solid line.
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ULTIMATE CAUSES OF SEX DIFFERENCES Parthenogenesi
s this is basically asexual reproduction in
vertebrates all offspring will be
female Polygamous having multiple mating
partners Sexual Selection a subset of Natural
Selection where selection pressures are based
upon the competition for obtaining mating
partners. PROXIMATE CAUSES OF SEX
DIFFERENCES Organizational / Activational
hypothesis behavioral sex differences result
from a) differential exposure to hormones that
act early in development to shape the brain and
nervous system guiding these behaviors, and b)
differential exposure to sex steroid hormones
later in life (puberty through adulthood)
activate the neural circuits shaped in (a)
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3.4 Gonadal development of the human embryo
All mammals start out being BIPOTENTIAL they
can develop into either the male or female
sex. The germinal ridge will be able to develop
into either primordial gonad once acted upon by
proteins produced in the body.
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• The bipotential nature of reproductive tissues
  early on is often referred to its anlagen a
  term relating to the dual primordial tissues and
  their predisposition to develop the secondary
  sexual characteristics.
• Mullerian duct system female accessory
  structures
• Wollfian duct system male accessory structures

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3.5 The Müllerian and Wolffian duct systems
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Female accessory sex structures are the default
pattern in mammals. But, due to the anlagen
effect (presence) of both systems early in
development, in rare circumstances, both systems
can develop in a single individual This leads
to potential hermaphroditism (now sometimes
called intersexism). There are variations in
the level of hermaphroditism. Partial
hermaphroditism is relatively more common. True
(full) hermaphroditism is exceptionally rare.
Hermaphroditic Lamb
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In the XY Sex Determining species, female
development is the default. Male development
requires testosterone and MIH (Mullerian
inhibitory hormone). The testosterone will
activate growth of the Wolffian duct
mophology. The MIH will cause regression of the
Mullerian duct morphology.
There are two pathways that occur simultaneously
to guide sexual differentiation. These are
referred to as 1. The masculinization
demasculinization continuum masculinization
induces male traits while demasculinization is
the removal of the potential for male
traits. 2. The feminization defeminization
continuum - feminization induces female traits
and defeminization is the removal of the
potential for female traits.
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3.6 Normal development of the accessory sex
organs
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3.7 Embryonic development of human external
genitalia
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3.8 Normal development of the external genitalia
Even in the external genitalia, there is a
continuum of development that is observed in
mammals.
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3.9 Sexual differentiation in humans
SRY the sex determining region on the Y
chromosome TDF testes determining factor GnRH
gonadotropin releasing hormone
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Aromatase Inhibitors - a class of drugs used
in the treatment of breast cancer and ovarian
cancer in postmenopausal women. Anastrozole
(Arimidex) Letrozole (Femara)
Exemestane (Aromasin) Vorozole (Rivizor)
Formestane (Lentaron) Fadrozole
(Afema) Some cancers require estrogen to grow.
Aromatase is an enzyme that facilitates the
synthesis of estrogen. Aromatase inhibitors block
the synthesis of estrogen. This lowers the
estrogen level, and slows the growth of estrogen
sensitive cancers. There are also naturally
occurring aromatase inhibitors in the body.
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Rat Developmental Time Line
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Study of the Pharmacological Agent ATD
Receives Exposure to ATD (an aromatase enzyme
inhibitor formally named 1,4,6
Androstatriene-Dione)
Pregnant Female Rat
Pups are born having been exposed to the ATD (the
aromatase enzyme inhibitor) developmentally
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Reproductive Behaviors
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3.15 Development of female copulatory behavior
requires active hormonal secretion
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3.16 Ovary and oviduct of a chicken
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3.18 Three types of male tree lizards
Territorial males Sedentary, non-territorial
males Nomadic non-territorial males -
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3.19 Temperature-dependent sex determination in
reptiles
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3.20 Aggression in adult female geckos
In this graph, you need to note The high
temperature range is a low-female population. The
low temperature is an all-female population.
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3.22 Freemartins
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Freemartins - an infertile female mammal which
has masculinized behavior and non-functioning
ovaries. Genetically and externally the animal
is female, but it is sterilized in the womb by
hormones from a male twin, becoming an infertile
partial intersex. Freemartinism is the normal
outcome of mixed-sex twins in all cattle species
that have been studied, and it also occurs
occasionally in other mammals including sheep,
goats and pigs. It is possible this may arise in
dizygotic mixed sex twins in humans as well,
although examples are limited
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3.23 LH profiles of female and male rats
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3.26 Experimental protocol
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3.27 Testosterone is a prohormone
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3.28 Rat pups gestating in utero
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3.29 Rough-and-tumble play behavior is
demasculinized in males by stress in utero
This study uses rats that were stressed in
utero. Similar studies have looked at human
populations that have undergone stress in utero.
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3.24 Positive feedback and the control of
ovulation
The lighter grey curved line from the Surge
Center is showing how it can, during ovulation,
direct a a much larger release of GnRH than
occurs in a typical pulsatile fashion from the
Pulse Center.
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3.25 The surge and pulse centers of the
hypothalamus
The Anteroventral periventricular preoptic area
(AVP of the POA) nucleus is believed to be the
site for the Surge Center in females that causes
the massive release of GnRH during ovulation.