1. Which of the following is TRUE regarding the genetics of sex?

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1 Neuroscience - Problem Drill 16: Determinants of Sexual Behavior and Gender Question No. 1 of Which of the following is TRUE regarding the genetics of sex? Question #01 (A) Only the sperm and the egg contain X and/or Y chromosomes. (B) Human chromosomes are numbered in order of decreasing size (except X and Y). (C) There are 40 human autosomes. (D) The male genotype is YY. (E) The genetic sex of a child is determined by the contribution of the mother. All human cells contain 46 chromosomes including the X and/or Y chromosomes. B. Correct! It is true that human chromosomes are numbered in order of decreasing size (except for X and Y chromosomes). There are 44 autosomes (22 pairs of matching chromosomes). The male genotype is XY (the X from the mother and the Y from the father). Because it is the chromosome from the father that can be either an X or a Y, and the contribution from the mother is always an X, the genetic sex of a child is determined by the contribution of the father. All of the information needed to build an individual is located within the DNA contained in the nucleus of every human cell. The DNA is organized into 46 chromosomes with 23 coming from the father and 23 coming from the mother. Therefore, each of us has two versions of each chromosome. The chromosomes are conveniently numbered in order of decreasing size with the only exception to this pair system being the sex chromosomes, X and Y. The usual way to state this occurrence is that there are 44 autosomes (22 pairs of matching chromosomes) and two sex chromosomes. Females have two X chromosomes (one from each parent) and males have one X chromosome from the mother and one Y chromosome from the father. Therefore, the female genotype is denoted XX and the male genotype is denoted XY. These genotypes specify a person s genetic sex. Because it is the chromosome from the father that can be either an X or a Y, the genetic sex of a child is determined by the contribution of the father. This is not the case for some other species (such as birds). The correct answer is (B).

2 Question No. 2 of 10 Instructions: (1) Read the problem and answer choices carefully, (2) Work the problems on paper as 2. Which of the following is FALSE regarding sexual development? Question #02 (A) The gonads are undifferentiated for the first 6 weeks of gestation. (B) The uncommitted gonads contain both a Mullerian and Wolffian duct. (C) Testosterone is produced if the fetus has a Y chromosome and a SRY gene. (D) In the presence of testosterone, the Wolffian duct develops into the male internal reproductive system. (E) The external genitals of both males and females develop from different undifferentiated urogenital structures. It is true that the gonads are undifferentiated for the first 6 weeks of gestation. It is true that the uncommitted gonads contain both a Mullerian and Wolffian duct. It is true that Testosterone is produced if the fetus has a Y chromosome and a SRY gene. It is true that in the presence of testosterone, the Wolffian duct develops into the male internal reproductive system. E. Correct! The external genitals of both males and females develop from the same undifferentiated urogenital structures. Unlike organs such as the lung and liver, the rudimentary cells that develop into the gonads are not committed to a single developmental pathway. During the first 6 weeks of pregnancy, the gonads are in an indifferent stage that can develop into either ovaries or testes. The uncommitted gonads possess two key structures, the Mullerian duct and the Wolffian duct. If the fetus has a Y chromosome and a SRY gene, testosterone is produced and the Wolffian duct develops into the male internal reproductive system. At the same time, the Mullerian duct is prevented from developing by a hormone called Mullerianinhibiting factor. Conversely, if there is no Y chromosome and no upsurge of testosterone, the Mullerian duct develops into the female internal reproductive system, and the Wolffian duct degenerates. The external genitals of both males and females develop from the same undifferentiated urogenital structures. The correct answer is (E).

3 Question No. 3 of 10 Instructions: (1) Read the problem and answer choices carefully, (2) Work the problems on paper as 3. Which of the following are TRUE regarding sex hormones? Question #03 (A) Aromatase is an enzyme found primarily in males. (B) Androgens are found only in males and progesterone only in females. (C) Sex hormones are synthesized from cholesterol. (D) Sex hormones act only on the cell membrane. (E) The gonadotropins include testosterone and estrogen. Females have an enzyme called aromatase, which will convert testosterone into estradiol. Both males and females produce progesterone and testosterone. C. Correct! Sex Hormones are steroids that are synthesized from cholesterol. Each sex hormone is just a small alteration in the basic cholesterol structure. Steroid hormones can easily pass through membranes and bind to receptors within the cytoplasm which gives them directly access to the nucleus and gene expression. LH and FSH together are referred to as the gonadotropins since they do affect the gonads. Sex Hormones are steroids that are synthesized from cholesterol. Each sex hormone is just a small alteration in the basic cholesterol structure. It is interesting to note that both males and females produce progesterone and testosterone but females also have an enzyme called aromatase, which will convert testosterone into estradiol. Although steroid sex hormones are often referred to as male and female please remember that men also have female hormones and women have male hormones. The designation as a male hormone merely reflects the act that men have higher concentrations of androgens, or male hormones, and women have more estrogens, or female hormones. Steroids act differently than other hormones because of their structure. While other hormones may be proteins and as such are unable to get through the cell membrane, steroid hormones can easily pass through membranes and bind to receptors within the cytoplasm which gives them directly access to the nucleus and gene expression. It is the differences in concentrations of the different receptors that results in steroid effects being localized to different areas of the brain. Of the large number of hormones synthesized in the parvocellular neurosecretory cells of the hypothalamus that affect the anterior pituitary, GnRH (gonadotropin releasing hormone) is the one that affects the anterior pituitary to release FSH (follicle stimulating hormone) and LH (luteinizing hormone). These two hormones together are referred to as the gonadotropins since they do affect the gonads. LH stimulates production of steroid sex hormones in both males (testosterone) and females (estrogens). FSH is required to initiate and maintain gametogenesis. FSH and LH act on gonads to produce androgens or estrogen and progesterone. These hormones have effects on germ cells and on many other tissues. The correct answer is (C).

4 Question No. 4 of Which of the following is NOT a phase in a sexual response cycle? Question #04 (A) Resolution (B) Arousal (C) Organsm (D) Recovery (E) Plateau Resolution is the final phase in the sexual response cycle. Arousal is the first phase in the sexual response cycle. Orgasm is the third phase in the sexual response cycle. D. Correct! Recovery is not one of the phases in the sexual response cycle. The plateau phase is the second phase in the sexual response cycle. Despite the obvious structural differences between the female and the male reproductive organs, their neural regulation is surprisingly similar. Sexual arousal of adult men and women can result from both erotic psychological and sensory stimuli and from tactile stimulation of the external sex organs. A full sexual response cycle consists of arousal followed by plateau, orgasm, and resolution phases. Although the duration of each phase can vary widely, the physiological changes associated with each one are relatively consistent. Neural control of the sexual response comes in part from the cerebral cortex but the spinal cord coordinates this brain activity with sensory information from the genitals and generates the critical outputs that mediate the sexual responses of the genital structures. The correct answer is (D).

5 Question No. 5 of Which of the following is controlled primarily by a sympathetic pathway? Question #05 (A) Engorgement (B) Mechanoreceptors in the external genitals. (C) Orgasm (D) Erection (E) Arousal Engorgement is controlled primarily by axons of the parasympathetic division of the ANS. The mechanosensory pathways from the genitals are components of the somatosensory system. C. Correct! As sensory axons become highly active, they together with the activity descending from the brain, excite sympathetic neurons in the thoracic and lumbar segments of the spinal cord that will trigger orgasm. Erection is controlled primarily by axons of the parasympathetic division of the ANS. Sexual arousal causes certain parts of the external genitals of both women and men to become engorged with blood, and thus to swell. The external genitals are densely innervated by mechanoreceptors. When we discuss the control of the reproductive organs, we will need to look at the circuits for the parasympathetic, sympathetic and sensory pathways. Sexual arousal causes certain parts of the external genitals of both women and men to become engorged with blood, and thus to swell. The external genitals are densely innervated by mechanoreceptors. Adequate stimulation of these sensory endings can, by itself, be enough to cause engorgement and erection. The mechanosensory pathways from the genitals are components of the somatosensory system and thus their anatomy follows the usual pattern: Axons from the mechanoreceptors in the genitals collect in the dorsal roots of the sacral and lumbar spinal cord. They then send branches into the dorsal horn of the cord, and into the dorsal columns, through which they project toward the brain. Engorgement and erection are controlled primarily by axons of the parasympathetic division of the ANS. The parasympathetic neurons can be activated by either the mechanosensory activity from the genitals or by axons descending from the brain. The parasympathetic nerve endings are thought to release a potent combination of acetylcholine, vasoactive intestinal polypeptide and nitric oxide that together cause a dramatic increase in blood flow into the erectile tissue. Completing the sexual response cycle requires activity from the sympathetic division of the ANS. As sensory axons become highly active, they together with the activity descending from the brain, excite sympathetic neurons in the thoracic and lumbar segments of the spinal cord that will trigger orgasm. The resolution phase includes a draining of the blood from the external genitals through veins, and a loss of erection and other signs and sensations of sexual excitement. The correct answer is (C).

6 Question No. 6 of Which of the following is an example of Polyandry? Question #06 (A) One female mating with many different males but each male mating with only one female. (B) One male and one female mating exclusively with each other. (C) One male mating with many different females but each female mating with only one male. (D) One male or female mating with many different partners of the opposite gender but members of the opposite gender mate with only one partner. (E) Males and females freely mating with many different partners of the opposite gender. A. Correct! Polyandry is involves one female mating with many different males but each male mating with only one female. One male and one female mating exclusively with each other is referred to as monogamy. One male mating with many different females but each female mating with only one male is referred to as polygyny. One male or female mating with many different partners of the opposite gender but members of the opposite gender mate with only one partner is referred to as polygamy. Polyamory refers to males and females freely mating with many different partners of the opposite gender. Mammals practice a huge range of mating behaviors. The ultimate, single evolutionary objective is to maximize the survival of offspring and parental genes. Most species practice one of two types of polygamy. They either practice polygyny in which one male mates with many females but each female mates with only one male, which is common with giraffes, orangutans and most other mammals; or they practice polyandry in which one female mates with many males but the male mates with only one female. Polyandry is rare with the main example being the phalarope, a shorebird that breed in the cold tundra. Other species practice monogamy in which the male and female tightly bond together and mate exclusively (at least temporarily) with each other. Usually, humans have a strong tendency toward monogamy although some cultures condone polygyny. Polyamory, in which males and females both mate with multiple partners is rarely seen in nature. Although there is much speculation about evolutionary explanations for the human mating patterns, determining the precise influences of genetics and culture on mating behaviors is virtually impossible. The correct answer is (A).

7 Question No. 7 of Which of the following is TRUE regarding sexual dimorphisms in humans? Question #07 (A) Sexual dimorphisms are very consistent across species and finding them in the brain is relatively easy. (B) Differences between human male and female brains tend to be very distinct without any overlap. (C) The behavior of males and females is usually very similar in regards to sexual reproduction behaviors. (D) In human brains, dimorphisms have so far proven to be small, subtle, few and of unknown function. (E) Finding sexual dimorphisms in humans would automatically lead to differences in behavior. Sexual dimorphisms vary widely across species and finding them in the brain is not always easy. Differences between human male and female brains tend to vary along a continuum with a great deal of overlap. The behavior of males and females is usually quite different in regards to sexual reproduction behaviors. D. Correct! It is true that in human brains, dimorphisms have so far proven to be small, subtle, few and of unknown function. While it is important to seek out sexual dimorphisms in humans, it is also important to understand these differences within their appropriate context. We know that behavior depends on the structure and function of the nervous system. We also know that the behavior of males and females is usually quite different in regards to sexual reproduction behaviors in all areas including finding, attracting, and keeping a mate; copulating; giving birth; and nursing and nurturing the offspring. Therefore, it is reasonable to expect that male and female brains are also somehow different; that they have sexual dimorphisms. Sexual dimorphisms vary widely across species and finding them in the brain is not always easy. In human brains, dimorphisms have so far proven to be small, subtle, few and of unknown function. Added to this is the fact that differences between human male and female brains tend to vary along a continuum with a great deal of overlap. A particular nucleus may be larger in women than in men on average, but size variations may be so great that many men have a larger nucleus than women. Therefore, while it is important to seek out sexual dimorphisms in humans, it is also important to understand these differences within their appropriate context. The correct answer is (D).

8 Question No. 8 of Which of the following is CORRECT regarding cognitive dimorphisms in humans? Question #08 (A) There are few reported differences in cognitive abilities between men and women. (B) All studies regarding cognitive dimorphisms are congruent. (C) Across large groups of people of both genders, there are very little individual differences. (D) The results of cognitive dimorphisms are always proven to be innate. (E) Reports of cognitive dimorphisms sometimes are accompanied by an evolutionary explanation. There are many reported differences in cognitive abilities between men and women. Not all studies yield the same results. In some cases one gender performs better, and in others, there is no difference. Across large groups of people of both genders, there are huge differences among individuals rather than being gender specific. It is important to look at the results in context of the question regarding if the differences are innate or a result of experiences. E. Correct! It is true that reports of cognitive dimorphisms sometimes are accompanied by an evolutionary explanation. There are many reported differences in cognitive abilities between men and women. Reports of cognitive dimorphisms sometimes are accompanied by an evolutionary explanation: men evolved as hunters and relied more on their abilities to navigate their environment while women evolved the behavior of staying close to home to care for the children so they were more social and verbal. These differences need to be viewed with caution for the following reasons: First, it is important to realize that when reading reports of cognitive dimorphisms, not all studies yield the same results. In some cases one gender performs better, and in others, there is no difference. Second, across large groups of people of both genders, there are huge differences among individuals rather than being gender specific. Third, it is important to look at the results in context of the question regarding if the differences are innate or a result of experiences. Neural circuitry can be influenced by experience. A common interpretation of gender-based differences in performance is that the distinctive hormonal environments, of male and female brains, not the gross anatomy of the CNS that make them work somewhat differently. Again, it is important to not over-generalize results based on this interpretation. The correct answer is (E).

9 Question No. 9 of Which of the following is FALSE regarding genetic/gender mismatches? Question #09 (A) It is possible for a genetic male to have a female brain. (B) In a genetic female (XX) with a male brain, treatment with testosterone early in development will have no effect on adult female sexual behavior. (C) Genetic males (XY) who carry a defective androgen receptor gene may have profound androgen insensitivity. (D) Occasionally, genetic females have a condition called congenital adrenal hyperplasia. (E) CAH females are exposed to abnormally high levels of circulating androgens early in their development and at birth, their external genitals are intermediate in size. Because hormones and not chromosomes largely determine the sexual characteristics of the nervous system, it is possible to have genetic males with female brains and genetic females with male brains. B. Correct! In all mammalian species studied, treatment with testosterone early in development leads to decreases in at least some features of adult female sexual behavior. Incorrect! It is true that genetic males (XY) who carry a defective androgen receptor gene may have profound androgen insensitivity. Incorrect! It is true that occasionally, genetic females have a condition called congenital adrenal hyperplasia (CAH). It is true that CAH females are exposed to abnormally high levels of circulating androgens early in their development and at birth, their external genitals are intermediate in size. Because hormones and not chromosomes largely determine the sexual characteristics of the nervous system, it is possible to have genetic males with female brains and genetic females with male brains. In all mammalian species studied, treatment with testosterone early in development leads to decreases in at least some features of adult female sexual behavior. Activating fully masculine behavior usually requires extended testosterone treatment before and after birth. Some humans also experience mismatches between their chromosomes and sex hormones. For example, genetic males (XY) who carry a defective androgen receptor gene may have profound androgen insensitivity. These individuals develop normal testes and produce ample testosterone but they appear outwardly quite female because their tissues cannot respond to androgen. At maturity, they develop like women, act like women, and even when they are aware of their biology, they prefer to call themselves women, dress like women and they choose men as their sex partners. Occasionally, genetic females have a condition called congenital adrenal hyperplasia (CAH) which literally means overgrown adrenal glands present at birth. Although they are genetically female, because their adrenal glands secrete unusually large amount of androgens, CAH females are exposed to abnormally high levels of circulating androgens early in their development. At birth, their external genitals are intermediate in size. Surgery an medications are the usual treatment after birth but CAH girls tend to be more aggressive and tomboyish in their behavior and a higher percentage of CAH women are homosexual compared to other women. However, caution needs to be exercised when drawing conclusions about the cause of human behavior. It is very hard to determine whether masculine behavior of a CAH female is due entirely to early androgen exposure and male-like brain dimorphisms, whether her behavior is the product of subtle difference in the way she is treated by others, or both. The correct answer is (B).

10 Question No. 10 of Which of the following is TRUE regarding estrogens and neurites? Question #10 (A) Estradiol treatment of tissue taken from the hypothalamus of newborn mice causes a great degree of neurite outgrowth. (B) Estradiol treatment decreases cell viability. (C) Estradiol treatment decreases dendritic spine density. (D) With an increase in esterdiol, cells seem to produce more of their neurotransmitter GABA. (E) It has been known for some time that estradiol also inhibits long-term synaptic plasticity in the hippocampus. A. Correct! It is true that estradiol treatment of tissue taken from the hypothalamus of newborn mice causes a great degree of neurite outgrowth. Estradiol treatment increases cell viability. Estradiol treatment increases dendritic spine density. With an increase in esterdiol, cells seem to produce less of their neurotransmitter GABA. It has been known for some time that estradiol also enhances long-term synaptic plasticity in the hippocampus. Estrogens have dramatic effects on the growth of neurites. Studies show that estradiol treatment of tissue taken from the hypothalamus of newborn mice causes a great degree of neurite outgrowth. Other studies have shown that estradiol increases cell viability and dendritic spine density. Taken together, these findings suggest that estrogens play an important role n forming neuronal circuitry during brain development. Further studies in adult rats showed the number of dendritic spines of neurons in the hippocampus of females fluctuated dramatically during the 5-day estrous cycle with the number of spines and the estradiol levels peaking together. Since spines are the major site of excitatory synapses on dendrites, this provides a possible explanation for the fact that hippocampal excitability also seems to track the estrous cycle. Indeed, experiments have found that as hippocampal neurons grow more spines, they also grow more excitatory synapses and seem to have more of the NMDA type of glutamate receptor. It has been known for some time that estradiol also enhances long-term synaptic plasticity in the hippocampus. Detailed experiments indicate it may do so by depressing synaptic inhibition since estradiol receptors in the hippocampus are primarily located within inhibitory interneurons. With an increase in esterdiol, these cells seem to produce less of their neurotransmitter GABA and therefore synaptic inhibition becomes less effective. Less inhibition in turn, leads to an increase in general neural activity which somehow triggers an increase in spines and excitatory synapses on the nearby pyramidal cells. We can only speculate about the behavioral significance of these results. In the rat, the hippocampus is particularly important for spatial memory and navigational skills. Since the peak in neural spine number coincides with the rat s peak in fertility, it may be that the female rat s brain may fine-tune itself on a 5-day cycle by heightening its spatial ability to seek out males. The correct answer is (A).