Chapter 10: Reproductive Behaviours

Question 1

What does the SRY gene do?

Answer 1

The SRY gene (sex-determining region on the Y chromosome) causes the undifferentiated gonad of a mammal to develop into a testis, which then produces testosterone and MIH to direct development toward the male pattern

Question 2

How do sex hormones affect neurons?

Answer 2

Sex hormones, which are steroids, bind to receptors on the membrane, activate certain proteins in the cell’s cytoplasm, and activate or inactivate particular genes.

Question 3

What would be the external genital appearance of a mammal exposed to high levels of both androgens and estrogens during early development? What if it were exposed to low levels of both?

Answer 3

A mammal exposed to high levels of both male and female hormones will appear male. One exposed to low levels of both will appear female. External genital development depends mostly on the presence or absence of androgens, and is nearly independent of estradiol levels.

Question 4

From the standpoint of protecting a male fetus’s sexual development, what are some drugs that a pregnant woman should avoid?

Answer 4

Pregnant women should avoid alcohol, marijuana, haloperidol, phthalates, and cocaine because these drugs interfere with male sexual development. Even aspirin and the chemicals lining bottles and cans produce mild abnormalities. Obviously, the results depend on both quantities and timing of exposure to these chemicals.

Question 5

How would the external genitals appear on a genetic female rat that lacked alpha-fetoprotein?

Answer 5

A female that lacked alpha-fetoprotein would be masculinized by her own estradiol, as researchers have in fact demonstrated (Bakker et al., 2006)

Question 6

Why is any individual’s brain more masculinized or feminized in some areas than others?

Answer 6

The mechanisms for sexual differentiation vary from one brain area to another. People vary in the genes, as well as the epigenetic influences, that modify brain development in different brain areas.

Question 7

What evidence most directly links children’s toy play to prenatal hormones?

Answer 7

Girls whose mothers had higher testosterone levels during pregnancy tend to play with boys’ toys more than the average for other girls.

Question 8

What are the effects of phthalates on sexual development?

Answer 8

Phthalates inhibit testosterone production. Boys whose mothers had higher phthalate exposure tend to play with boys’ toys less than the average for other boys.

Question 9

By what mechanism does testosterone affect the hypothalamic areas responsible for sexual behavior?

Answer 9

Testosterone primes hypothalamic cells to be ready to release dopamine

Question 10

What are two explanations for why married men tend to have lower testosterone levels than single men?

Answer 10

First, marriage decreases the need to seek sexual partners and therefore may lower the testosterone level. Second, men with lower testosterone levels are more likely to marry and remain married.

Question 11

At what time in a woman’s menstrual cycle do her estradiol levels increase? When are they lowest?

Answer 11

Estradiol levels increase during the days leading up to the middle of the menstrual cycle. They are lowest during and just after menstruation.

Question 12

When is a woman most likely to act sexy and initiate sexual activity?

Answer 12

During the periovulatory period.

Question 13

What factors are responsible for maternal behavior shortly after rats give birth? What factors become more important in later days?

Answer 13

The early stage of rats’ maternal behavior depends on a surge in the release of the hormones prolactin and estradiol. A few days later, her experience with the young decreases the responses that would tend to make her reject them. Experience with the young maintains maternal behavior after the hormone levels begin to drop.

Question 14

Mark is about to enter puberty. Which of the following is NOT an organizing effect that he should expect?
a. Penis growth
b. Facial hair
c. Changes in male–female differences in the anatomy of the hippocampus
d. A change in his voice

Answer 14

changes in male-female differences in the anatomy of the hippocampus

Correct. Mark should expect that the hormones at puberty will produce facial hair and penis growth, as well as changes in his voice. Also, he will experience male–female differences in the anatomy of certain parts of the hypothalamus.

Question 15

During her menstrual cycle, Anne’s anterior pituitary will release ____ to promote the growth of a follicle in the ovary. The developing follicle will begin to release more and more estradiol. This will result in the anterior pituitary releasing ____. This will allow Anne to release an ovum.
a. estrogen; LH
b. estrogen; FSH
c. FSH; LH
d. LH; FSH

Answer 15

FSH; LH
Correct. Approximately every 28 days, Anne has a menstrual cycle, a periodic variation in hormones and fertility. To release an ovum, she will need to release follicle-stimulating hormone (FSH) that will ultimately lead to the release of luteinizing hormone (LH).

Question 16

Professor Case is studying maternal behaviors in mice. He has shown that mother mice will secrete prolactin, which inhibits sensitivity to _____, encouraging the mother to eat more than usual.
a. oxytocin
b. leptin
c. estradiol
d. vasopressin

Answer 16

Leptin

Correct. Professor Case has discovered that after a mouse mother delivers her babies, she increases her secretion of oxytocin and prolactin, which promote milk production and several aspects of maternal behavior. Prolactin also inhibits sensitivity to leptin, enabling the mother mice to eat more than usual.

Question 17

What evolutionary advantage is suggested for why women are more interested in men’s wealth and success than men are interested in women’s wealth?

Answer 17

During pregnancy and early child care, a female is limited in her ability to get food and therefore prefers a male partner who can provide for her. A healthy male is not similarly dependent on a female.

Question 18

What is a common cause for a genetic female (XX) to develop a partly masculinized anatomy?

Answer 18

If a genetic female is genetically deficient in her ability to produce cortisol, the pituitary gland does not receive negative feedback signals and therefore continues stimulating the adrenal gland. The adrenal gland then produces large amounts of its other hormones, including testosterone, which masculinizes development.

Question 19

If a genetic female is exposed to extra testosterone during prenatal development, what behavioral effect is likely?

Answer 19

A girl who is exposed to extra testosterone during prenatal development is more likely than most other girls to prefer boy-typical activities.

Question 20

What would cause a genetic male (XY) to develop a partly feminized external anatomy?

Answer 20

A genetic male with a gene that prevents testosterone from binding to its receptors will develop an appearance that partly or completely resembles a female.

Question 21

When children who had been reared as girls reached puberty and grew a penis and scrotum, what happened to their gender identity?

Answer 21

Most changed their gender identity from female to male.

Question 22

For which kind of twin pair is the concordance for sexual orientation greatest?

Answer 22

Monozygotic twins have higher concordance than dizygotic twins. Be sure to state this point correctly: Do not say that homosexuality is more common in monozygotic than dizygotic twins. It is the concordance that is greater—that is, the probability that both twins have the same sexual orientation

Question 23

It seems difficult to explain how a gene could remain at a moderately high frequency in the population if most men with the gene do not reproduce. How would the hypothesis about epigenetics help with the explanation?

Answer 23

According to this hypothesis, some unidentified event in the environment can attach an acetyl group or a methyl group to some gene, increasing or decreasing its activity. That gene modification could be passed to the next generation, producing evidence for a hereditary effect, even though there is no “gene for homosexuality.” If events like this happen often enough, the result could be a moderately high prevalence of homosexuality, even if men with the inactivated gene seldom reproduce.

Question 24

By what route might having an older brother increase the probability of male homosexuality?

Answer 24

Having an older brother might increase the probability of male homosexuality by altering the mother’s immune system in the prenatal environment. The effect of the older brother does not depend on growing up in the same home

Question 25

How might stress to a pregnant rat alter the sexual orientation of her male offspring?

Answer 25

Evidently, the stress increases the release of endorphins in the hypothalamus, and very high endorphin levels can block the effects of testosterone.

Question 26

In LeVay’s study, what evidence argues against the idea that INAH-3 volume depends on AIDS rather than sexual orientation?

Answer 26

In his study, the average size of INAH-3 was about the same for heterosexual men who died of AIDS and those who died of other causes. One homosexual man who died of other causes had about the same size INAH-3 as homosexual men who died of AIDS.

Question 27

From an evolutionary standpoint, which is most true?
a. Men are more jealous of a wife’s possible infidelity.
b. Women are more jealous of a husband’s possible infidelity.
c. Both are equally jealous.
d. Women are more jealous, but conceal their jealousy so it seems as if men are more jealous

Answer 27

Correct. If a man is to pass on his genes, he needs to be sure that the children he supports are his own. An unfaithful wife threatens that certainty. A woman knows that any children she bears are her own, so she does not have the same worry.

Question 28

Taylor was born with an XY chromosome pattern; however, Taylor lacks the receptors that allow the androgen hormones to activate genes. He/she would _____.
a. be androgen insensitive
b. have low levels of testosterone
c. have too much estrogen
d. develop as a typical male

Answer 28

be androgen insensitive

Correct. Taylor produces normal amounts of androgens, but lacks the receptor for them. Therefore he/she has a condition known as androgen insensitivity or testicular feminization. It can occur in various degrees, resulting in anatomy that ranges from a smaller than average penis to genitals like those of a typical female. At puberty, Taylor wouldn’t menstruate because the body would have internal testes instead of ovaries.

Question 29

Which of the following is NOT a way in which stress and alcohol alter brain development?
a. Stress releases endorphins, which can antagonize the effects of testosterone on the hypothalamus.
b. The long-term effects of either prenatal stress or alcohol include several changes in the structure of the nervous system, making the affected males’ anatomy closer to that of females.
c. Stress also elevates levels of certain adrenal hormones that decrease testosterone release.
d. Stress results in excessive estradiol release that feminizes the brain.

Answer 29

stress results in excessive estradiol release that feminizes the brain

Correct. Research in laboratory animals has shown that prenatal stress alters sexual development. It has been demonstrated that stress disrupts normal testosterone release and activation. And stress and alcohol use can alter the structure of the nervous system.