Bio 27: September 26, 2012

Chapter 5: Gender Issues

Exam grades• Mean exam score:

61.2% (D)• Median exam score:

65% (C)• Grading scheme:

≥85% = A75–84.99% = B65–74.99% = C50–64.99% = D

<50% = F A B C D F0

2

4

6

8

10

12

14

16

Course grades• Mean course score:

69.32% (C)• Median course score:

75.93% (B)• Grading scheme:

≥85% = A75–84.99% = B65–74.99% = C50–64.99% = D

<50% = F A B C D F0

2

4

6

8

10

12

14

16

Sex and Gender: some definitions

• Sex: biological female or maleness– genetic sex: determined by sex chromosomes– anatomical sex: determined by physical differences

• Gender: psychosocial meaning of maleness and femaleness; masculinity or femininity

• Gender Identity: each person’s subjective sense of being male or female

• Gender Roles: the cultural norms for male and female behavior

Chromosomal sex

• Humans have 23 pairs of chromosomes– 22 autosomes and 1

sex chromosome• Chromosomal sex

– XX: female• DSS gene on X

– XY: male• SRY gene on Y

– XXX: female– X only : female– Y only: lethal

Gonadal sex• We all begin life with gonads that are not sex-specific!• The SRY gene on the Y chromosome, if present, encodes

proteins that initiate the conversion of the gonads into testes

• In the absence of the SRY gene, the gonads become ovaries

Hormonal sex

• Once they begin to differentiate the gonads start to secrete hormones:– Ovaries: mostly estrogens and progestins– Testes: mostly androgens, including testosterone

• These hormones influence development of the internal & external genitalia

Hormones promote differentiation of the internal genitalia

Androgens present: disappearance of the Müllerian duct and maturation of the Wolffian ductAndrogens absent: disappearance of the Wolffian duct and maturation of the Müllerian duct

Hormones promote differentiation of the external genitalia

Homologous Sex Organs

Sex differences in the brain• Females and males have differences in their brain

structure; these differences seem to be influenced by androgens (testosterone) and estrogens

• These differences include:– Males have slightly larger brains than females– A region of the brain called the hypothalamus seems to

become less sensitive to estrogens in males– An area of the hypothalamus called the bed nucleus of the

stria terminalis (BST) is sensitive to androgens and estrogens and seems to influence sex differences and sexual functioning

– Another area of the hypothalamus, the preoptic area (POA), also shows differences in men and women

Other brain areas also differ• Cerebral cortex is the brain area

associated with “higher mental processes” like memory, perception, and thought

• The left and right sides of the cortex show specialization; the two sides are connected by a structure called the corpus callosum

• Males tend to have a larger right cortex and females a larger corpus callosum

• Women and men tend to use their brains differently when solving problems

Male and female brains?

• Findings of differences in brain function in males and females are controversial

• Our brains learn things by physically changing; our brains respond to many stimuli, including social messages

• Females often tend to score higher in verbal skills, and males in math skills, although females and males typically have similar math scores until around puberty

• Are these innate differences or learned differences?

Typical Prenatal Differentiation

ATYPICAL PRENATAL DIFFERENTIATION

Intersexed individuals

• Intersexed individuals are classified as:– True hermaphrodites: have both ovarian and

testicular structures in their bodies; extremely rare!– Pseudohermaphrodites: occurs 1 in every 2,000

births; have gonads that match chromosomal sex but ambigulous internal and external genitalia

Atypical Prenatal Differentiation

• Sex chromosome disorders:– Turner’s syndromeXO: 1 in every 2500–3000

females; develop typical female external genitals, but internal genitalia and gonads are not fully developed. Women with this syndrome do not develop breasts at puberty or menstruate.

– Klinefelter’s syndrome XXY: 1 in every 1000 males; develop male external genitalia, but are typically sterile with smaller than normal penises and testes. Usually identify as male but some have gender-identity issues

Disorders affecting prenatal hormonal processes

• Androgen insensitivity syndrome (AIS): Individuals are chromosomally male, but due to a mutation in their androgen receptors develop as females; have “blind” vaginas and undescended, undeveloped testes

Atypical Prenatal Differentiation

Homework assignment #3: due at the beginning of class 10/3/12

What people and other influences have influenced your own gender role development? Think about both positive and negative influences that shaped your gender role. What do you feel are the benefits and consequences of being the gender you are?

400-700 words