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Lecture 13

PSYC 211 Lecture 13: Reproductive System
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by OneClass2322298 , Fall 2017
12 Pages
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Fall 2017

Department
Psychology
Course Code
PSYC 211
Professor
Jonathan Britt
Lecture
13

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Reproduction
Overview
Reproductive behaviours constitute most important category of social behaviours, because
without them, most species would not survive
These behaviours include flirting, mating, parental behaviour, and most forms of aggressive
behaviours - aggression is most related to animal's desire to have sex or defend their offspring
These behaviours are the most striking categories of sexually dimorphic behaviours
Sexual dimorphic behaviours - behaviour that has different forms (or that occurs with different
probabilities or under different circumstances) in males and females
Differences between males and females
Sex differences in anatomy
o Usually very different anatomical features of males and females throughout the animal
kingdom (colour and presentation, body size; in some species male can fly and the female
can't)
o The Triplewart Seadevil
The female is large and has a light on the top of her head
The male is a tiny sperm-producing appendage that lives on the females back
parasitically
No rules in the animal kingdom that males and females have to act or look anything alike at all -
there can be very dramatic differences
o Typically in the mammalian kingdom the differences are not as dramatic
Humans
In terms of behaviour, there are differences between sexes, on average, in their mixture of
talents, temperaments, and interests
These differences can be the result of biology, socialization, or culture and the interaction of the
two or three
o The extent to which the differences are influenced by any of these factors is unclear
o Historically we used to think that the biological differences between men and women were
so important that men and women should be treated differently from birth onward
o Over time, people have come to appreciate the social and cultural influence - these are
much more important (but biological differences are still real and still important)
Differences between the sexes on behavioural traits (i.e. talents, interests, etc.) are caused by
biological differences
o People have assumed the biological differences are so important in driving these
behavioural differences, but they've been misguided over time (proved wrong all the time)
o Now we assume any differences are a result of socialization and culture
Men and women have specific, hard-wired differences in both their bodies and brains
o Exposure to sex hormones, both before and after birth, is responsible for this sexual
dimorphism
General intelligence (or the aptitude to perform any particular job) is not located in a single
neuroanatomical structure
o Traits like general intelligence are hard to define and measure
o We know that very different brains can produce similar levels of intellectual performance
Sexual Reproduction - DNA
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The X and Y chromosomes are the sex chromosomes
o Typically determine an organism's sexual identity
Mature reproductive cells (gametes - sperm or ova) only have one copy of every chromosome
o These reproductive cells, made in the gonads (ovaries or testes)
All our cells have 46 chromosomes - 2 copies of each chromosome
Gametes only have 1 copy of each chromosome, so they only have 23 chromosomes
Through sexual reproduction, the sperm and the ova meet to create offspring, which creates the
46 chromosomes
Through sexual production, a person either has XX or XY in DNA
Embryonic Sex Organs
To appreciate the biological differences between males and females, it's helpful to understand the
differential development of the sexes
All embryos contain precursors for both female and male sex organs (for the first 2 months)
but during third month of gestation one of these precursors typically develops while the other
withers away
Müllerian s ys tem - embryonic precursors of female internal sex organs
Wolffian system - embryonic precursors of male internal sex organs
o 1st 2 months embryos have both
Sex determination
In humans, biological sex is determined by five factors present at birth
1. Sex chromosomes: XX or XY
2. Gonads: testes or ovaries
3. Sex hormones: androgen signaling
4. Internal reproductive anatomy
5. External anatomy
The 5 factors are generally all male or all female
There is going to be differences in DNA - this triggers undifferentiated gonad tissue to develop into
testes of ovaries
o Then there is either going to be a release of sex hormones or not
o Release of sex hormones triggers differences in internal sex organs and external anatomy
There is a signaling cascade (molecules released, bind to receptors, cause activity) that produces
characteristics where the 5 factors are all either going to be male or female
Unexpected combinations in the 5 factors cause intersex conditions, in which the person cannot
be distinctly identified as male or female
o Often relate to gender identity and sex orientation
Some biological differences seem to be hard-wired and difficult to change
o One of these is gender identity and sexual orientation
Transgender is when people identify with a gender that is different than the gender they were
classified as at birth
3 categories of sex organs (sex of the person refers to:) are the gonads, internal reproductive
anatomy and the external reproductive anatomy
o Differentiated by the biological signaling cascades that regulate them
o Distinct cascades
Female Sex Organ Development
XX chromosome (need 2 X chromosomes to trigger the development of ovaries) --->
development of ovaries ---> which are largely silent (once developed) until puberty (in which they
find more resources at oneclass.com
find more resources at oneclass.com
become active) ---> puberty is triggered by hormones released from gonads (ovaries) and the
sudden onset of ovary function (true for both females and males)
o If you do not have 2 X chromosomes, you will not have ovaries
The Müllerian sys tem will develop into internal female s ex organs
o Internal female sex organs develop in the absence of anti-Müllerian hormone
o Includes the (inner) vagina, uterus, and fallopian tubes
The Wolffian system - without any signaling will wither away on its own
External female sex organs (the vulva) develop in the absence of androgen hormones (male
hormone release by testes)
If the ovaries don't do anything until puberty, what triggers development of female sex organs?
o The absence of hormone signaling
Male Sex Organ Development
One specific gene on the Y chromosome know as the SRY gene; encodes a protein that causes the
undifferentiated fetal gonads to develop into testes - regardless of how many X's a person has
This gene overpowers XX-ovary instructions, so XXY individuals develop testes
SRY gene ---> development of testes ---> embryonic testicular release of: (1) anti-Müllerian
hormone --> s tops development of Müllerian s ys tem (internal female sex organs) and (2)
androgens (testosterone) --> triggers development of male sex organs (both internal and external)
SO:
o Presence of SRY gene on the Y chromosome causes the development of testes
o The Anti-Müllerian hormone s huts down the female sys tem (withers away)
o Another hormone (androgens) cause the Wolffian system to develop into internal sex
organs as well as the external organs
2 hormones have different effects
Defeminizing effect - effect of anti-Müllerian hormone early in development, which prevents
development of the internal anatomy typical of females
o Shuts down system
Masculinizing effect - effect of androgen hormones early in development, which promotes
anatomical and behavioural characteristics typical of males
o Activates system
Androgens - male sex steroid hormones (2 main ones)
o Testosterone is the principle mammalian androgen
o Dihydrotestosterone is also one that is made from testosterone
It triggers development of male external sex organs
These hormones also have effects on brain anatomy which will influence behaviour
Organizational effects of androgens on behavioural masculinization and defeminization
Behavioural defeminization - the organizational effect of androgens on the brain that prevent
animals from displaying female-typical behaviours in adulthood
Behavioural masculinization - organizational effect of androgens on the brain that enables
animals to engage in male-typical behaviours in adulthood
Sexual Orientation and the Brain
The human brain is a sexually dimorphic organ
The sizes (of nuclei) and interconnectivity of different brain regions vary according to biological
sex and sexual identity
Some of the differences between males and female brains are clearly caused by genetic and
hormonal differences during development
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Description
Reproduction Overview Reproductive behaviours constitute most important category of social behaviours, because without them, most species would not survive These behaviours include flirting, mating, parental behaviour, and most forms of aggressive behaviours - aggression is most related to animal's desire to have sex or defend their offspring These behaviours are the most striking categories of sexually dimorphic behaviours Sexual dimorphic behaviours - behaviour that has different forms (or that occurs with different probabilities or under different circumstances) in males and females Differences between males and females Sex differences in anatomy o Usually very different anatomical features of males and females throughout the animal kingdom (colour and presentation, body size; in some species male can fly and the female can't) o The Triplewart Seadevil The female is large and has a light on the top of her head The male is a tiny sperm-producing appendage that lives on the females back parasitically No rules in the animal kingdom that males and females have to act or look anything alike at all - there can be very dramatic differences o Typically in the mammalian kingdom the differences are not as dramatic Humans In terms of behaviour, there are differences between sexes, on average, in their mixture of talents, temperaments, and interests These differences can be the result of biology, socialization, or culture and the interaction of the two or three o The extent to which the differences are influenced by any of these factors is unclear o Historically we used to think that the biological differences between men and women were so important that men and women should be treated differently from birth onward o Over time, people have come to appreciate the social and cultural influence - these are much more important (but biological differences are still real and still important) Differences between the sexes on behavioural traits (i.e. talents, interests, etc.) are caused by biological differences o People have assumed the biological differences are so important in driving these behavioural differences, but they've been misguided over time (proved wrong all the time) o Now we assume any differences are a result of socialization and culture Men and women have specific, hard-wired differences in both their bodies and brains o Exposure to sex hormones, both before and after birth, is responsible for this sexual dimorphism General intelligence (or the aptitude to perform any particular job) is not located in a single neuroanatomical structure o Traits like general intelligence are hard to define and measure o We know that very different brains can produce similar levels of intellectual performance Sexual Reproduction - DNA The X and Y chromosomes are the sex chromosomes o Typically determine an organism's sexual identity Mature reproductive cells (gametes - sperm or ova) only have one copy of every chromosome o These reproductive cells, made in the gonads (ovaries or testes) All our cells have 46 chromosomes - 2 copies of each chromosome Gametes only have 1 copy of each chromosome, so they only have 23 chromosomes Through sexual reproduction, the sperm and the ova meet to create offspring, which creates the 46 chromosomes Through sexual production, a person either has XX or XY in DNA Embryonic Sex Organs To appreciate the biological differences between males and females, it's helpful to understand the differential development of the sexes All embryos contain precursors for both female and male sex organs (for the first 2 months) but during third month of gestation one of these precursors typically develops while the other withers away M llerian system - embryonic precursors of female internal sex organs Wolffian system - embryonic precursors of male internal sex organs o 1st 2 months embryos have both Sex determination In humans, biological sex is determined by five factors present at birth 1. Sex chromosomes: XX or XY 2. Gonads: testes or ovaries 3. Sex hormones: androgen signaling 4. Internal reproductive anatomy 5. External anatomy The 5 factors are generally all male or all female There is going to be differences in DNA - this triggers undifferentiated gonad tissue to develop into testes of ovaries o Then there is either going to be a release of sex hormones or not o Release of sex hormones triggers differences in internal sex organs and external anatomy There is a signaling cascade (molecules released, bind to receptors, cause activity) that produces characteristics where the 5 factors are all either going to be male or female Unexpected combinations in the 5 factors cause intersex conditions, in which the person cannot be distinctly identified as male or female o Often relate to gender identity and sex orientation Some biological differences seem to be hard-wired and difficult to change o One of these is gender identity and sexual orientation Transgender is when people identify with a gender that is different than the gender they were classified as at birth 3 categories of sex organs (sex of the person refers to:) are the gonads, internal reproductive anatomy and the external reproductive anatomy o Differentiated by the biological signaling cascades that regulate them o Distinct cascades Female Sex Organ Development XX chromosome (need 2 X chromosomes to trigger the development of ovaries) ---> development of ovaries ---> which are largely silent (once developed) until puberty (in which theybecome active) ---> puberty is triggered by hormones released from gonads (ovaries) and the sudden onset of ovary function (true for both females and males) o If you do not have 2 X chromosomes, you will not have ovaries The Mllerian system will develop into internal female sex organs o Internal female sex organs develop in the absence of anti-Mllerian hormone o Includes the (inner) vagina, uterus, and fallopian tubes The Wolffian system - without any signaling will wither away on its own External female sex organs (the vulva) develop in the absence of androgen hormones (male hormone release by testes) If the ovaries don't do anything until puberty, what triggers development of female sex organs? o The absence of hormone signaling Male Sex Organ Development One specific gene on the Y chromosome know as the SRY gene; encodes a protein that causes the undifferentiated fetal gonads to develop into testes - regardless of how many X's a person has This gene overpowers XX-ovary instructions, so XXY individuals develop testes SRY gene ---> development of testes ---> embryonic testicular release of: (1) anti-Mllerian hormone --> stops development of Mllerian system (internal female sex organs) and (2) androgens (testosterone) --> triggers development of male sex organs (both internal and external) SO: o Presence of SRY gene on the Y chromosome causes the development of testes o The Anti-Mllerian hormone shuts down the female system (withers away) o Another hormone (androgen
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