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Lecture 13

PSYC 211 Lecture 13: Reproductive System

12 Pages

Course Code
PSYC 211
Jonathan Britt

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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 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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