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Psychology 2035A/B Lecture Notes - X Chromosome, Sexual Differentiation, Prenatal Development

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Doug Hazlewood

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Sex & Gender - Becoming Male or Female: The Role of Biology and
Part 1: Reproductive Biology: Prenatal Sexual Differentiation
Begins at conception (sperm fertilizes egg)
Mother’s egg (“X” sex chromosome) - every child receives x chromosome
from mother
Father’s sperm (“X” or “Y” sex chromosome)
If x sperm fertilizes egg: genetic female (xx)
If a y sperm fertilizes egg: genetic male (xy)
A. The Genetic Factor - represents the first step in becoming a male or
but you’re not a male or female yet, because for several weeks after this,
you won’t have any sex organs
B. The Gonadal Factor (development of reproductive organs: testes or
ovaries) - depends on whether the y chromosome is present or active
If present - (a) stimulates the development of the testes;
(b) inhibits the development of the ovaries
we see this most clearly when problems occur: “True Hermaphrodites” -
genetic female (xx); with tiny piece of y chromosome attached (XXy)
y chromosome big enough to stimulate the development of testes.
Not big enough to inhibit development of ovaries (therefore BOTH)
- doesn’t happen very often
C. The Hormonal Factor (development of sex organs: penis or clitoris and
Testes produce androgens (male sex hormone)
When androgens are present; penis develops; (sometimes called the
Adam Principle)
When absent; clitoris and vagina develop - called the Eve Principle
Problems can occur:

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(a) The Adrenogenital Syndrome:
genetic female with unusually active adrenal glands (produce androgens);
fetus develops sex organs that appear to be “male” (clitoris is enlarged,
vagina is fused (no clear opening) - individual doesn’t have testes
because they are a genetic female
(b) Androgen-insensitivity syndrome:
genetic male with normal testes that produce normal levels of androgens;
but body is insensitive to androgens (like the androgens are not present)
and therefore develops sex organs that have a “female” appearance -
testes are there but they remain up in the body, “vagina” lacks any depth
women were given progestin to prevent miscarriages - was actually
producing large quantities of androgens and then creating Androgenital
if everything goes as planned, you are now a biological “male” or “female”
(end of prenatal sexual differentiation)
But, for the next decade, you can’t reproduce
D. The Puberty Factor (involves hormones)
Girls (age 10-12); Boys (12-14)
(a) development of secondary sex characteristics - boys and girls: pubic
hard, growth spurt
girls: breast development
Boys: facial hair, deeper voice, larger penis
(b) gonads (reproductive organs) mature:
menstruation in girls (mature eggs are released from ovaries);
the first ejaculation in boys (production of mature sperm from
each of us has two basic identities
Part 2: Our Two Basic Identities
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