Mastering 12

Which of the following would be most likely to lead to cancer?

amplification of a proto-oncogene and inactivation of a tumor-suppressor gene (Excess copies of the proto-oncogene could stimulate cell division abnormally, and the inactivation of a tumor-suppressor gene would eliminate a brake on cell division.)

Homologous chromosomes migrate to opposite poles during _____.

anaphase I

During _____ sister chromatids separate.

anaphase II (Anaphase II is essentially the same as mitotic anaphase except that the cell is haploid.)

Which hormone(s) is(are) directly responsible for triggering the development of the secondary sex characteristics of males, such as beard growth?

androgens (Androgens, such as testosterone, are responsible for both sperm production and the secondary sex characteristics of males.)

What name is given to this process (budding)?

asexual reproduction

Suppose you wanted to start an animal-breeding business. For most of the following animals, you could start out with just a single animal. Which of the animals below would require that you start with at least two individuals?

frogs

The "reproductive handicap" for sexual reproduction refers to _____.

have only half the offspring are females (A female undergoing asexual reproduction would have offspring that have 100% of her genes, whereas a sexually reproducing female typically passes only 50% of her genetic material to her offspring.)

Sexual reproduction includes a reproductive pattern called _____.

hermaphroditism (In hermaphroditism a single individual produces both sperm and ova; although some individuals fertilize themselves, most must mate with another member of the same species.)

If there is fertilization, secretion of _____ by the early embryo maintains the corpus luteum.

human chorionic gonadotropin (HCG, secreted by the early embryo, maintains the corpus luteum. The corpus luteum secretes estrogen and progesterone, which maintain the endometrium for implantation.)

During human gestation, rudiments of all organs develop

in the first trimester.

A rapid increase in the _____ level stimulates ovulation.

luteinizing hormone

Human gametes are produced by _____.

meiosis (Meiosis produces haploid gametes from a diploid parental cell.)

If you look through a microscope and see chromosomes lined up two by two, what stage of cellular reproduction must you be looking at?

meiosis I only

For which of the following is the number the same in spermatogenesis and oogenesis?

meiotic divisions required to produce each gamete

During _____ chromosomes align single file along the equator of a haploid cell.

metaphase II

Of the two processes we learned about which is gong on in my hand right now?

mitosis

The secretion of androgens is regulated by a _____ feedback mechanism involving the _____ and _____.

negative ... hypothalamus ... pituitary gland (An increase in androgens inhibits the secretion of releasing hormones by the hypothalamus and LH secretion by the pituitary gland. A decrease in androgens stimulates the secretion of releasing hormones by the hypothalamus and LH secretion by the pituitary gland.)

In humans, oogenesis in comparison to spermatogenesis is different in that _____.

oogenesis does not complete meiosis until after fertilization, but spermatogenesis is complete before the sperm leave the body

What is the usual site of the fertilization of an egg cell?

oviduct

The anatomical location for the typical union of a sperm and an egg (conception) is the _____.

oviducts (Ovulation releases the eggs into the abdominal cavity, where they are swept into the oviduct.)

The increased levels of ____________________ in the second half of the cycle inhibit secretion of FSH and LH and promote maintenance of the endometrium.

progesterone

Synapsis occurs during _____.

prophase I

During _____ a spindle forms in a haploid cell.

prophase II

Which of the following correctly traces the path of sperm from their site of production to their exit from a man's body?

seminiferous tubule → epididymis → vas deferens → urethra (Sperm are produced in the seminiferous tubules, mature in the epididymis, and during ejaculation pass through the vas deferens into the urethra.)

Which of the following is not properly paired?

seminiferous tubule-cervix (testosterone-estradiol vas deferens-oviduct scrotum-labia majora Sertoli cells-follicle cells all are paired correctly)

Sperm develop in the _____.

seminiferous tubules

Salamander and insect populations consisting only of genetically identical females lack males because _____.

sperm do not fuse with eggs during reproduction, but the eggs develop into embryos anyway

At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.

telophase I

At the end of _____ and cytokinesis there are four haploid cells.

telophase II

Synapsis

the pairing of homologous chromosomes, occurs during prophase I

Peaks of LH and FSH production occur during

the period just before ovulation

Human pregnancy is indicated by the presence of chorionic-gonadotropin metabolites in the urine until _____.

the placenta takes over for the ovaries in producing the steroid hormones needed during pregnancy (Prior to the full development of the placenta at the end of the first trimester, chorionic gonadotropin is needed to stimulate steroid hormone production in the ovaries.)

In male mammals, excretory and reproductive systems share

the urethra.

An oocyte released from a human ovary enters the oviduct as a result of

the wavelike beating of cilia lining the oviduct.

Meiosis I produces _____ cells, each of which is _____.

two ... haploid

Sperm exit a male's body via the _____.

urethra

A fertilized egg usually implants itself and develops in the _____.

uterus

Which of the following characterizes parthenogenesis?

An egg develops without being fertilized.

Meiosis II typically produces _____ cells, each of which is _____.

four ... haploid

If the hypothetical organism has 5 chromosomes in one of its gametes, then it must have ______ chromosomes in a body cell just before mitosis

10 (just before mitosis, the chromosomes in a body cell are duplicated, but the sister chromatids remain joined together. So you will see 10 (duplicated) chromosomes in a typical body cell.)

Ovulation usually occurs on or about day _____ of a 28-day ovarian cycle.

14

A diploid organism whose somatic (nonsex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.

16

Normal human gametes carry _____ chromosomes.

23

Which of these gametes contains one or more recombinant chromosomes? The figure shows 2 cells which undergo meiosis. A cell on the left has 4 chromosomes (from left to right and from top to bottom): large blue, large red, small blue, and small red. After two meiotic divisions, 4 cells labeled A to D are formed. Cell A contains 1 large blue and 1 small blue chromatid. Cell B contains 1 large blue and 1 small blue chromatid. Their ends of arms were replaced with parts of the homologous red chromosomes. Cell C contains, vice versa, 1 large red and 1 small red chromatid partially replaced with blue DNA. Cell D contains 1 large red and 1 small red chromatid. The other parental cell (on the right) has 4 chromosomes as well (from left to right and from top to bottom): large red, large blue, small blue, and small red. After two meiotic divisions, 4 cells are formed, one of which is labeled E. This cell contains 1 large red and one small blue chromatid.

B and C

Which of the following statements about oogenesis in humans is true?

Beginning at puberty, a primary oocyte completes its first meiotic division to form a secondary oocyte and a polar body approximately every month. (This secondary oocyte is released into the oviduct during ovulation and then begins meiosis II, which is not complete unless the oocyte is fertilized by a sperm cell.)

The following processes are associated with meiosis and the sexual life cycle: DNA replication before meiosis crossing over chromosome alignment in metaphase I and separation in anaphase I chromosome alignment in metaphase II and separation in anaphase II fertilization Sort each process into the appropriate bin according to whether it contributes to heredity only, genetic variation only, or both. (Note that a bin may be left empty.)

Both: DNA replication before meiosis crossing over chromosome alignment in metaphase I and separation in anaphase I chromosome alignment in metaphase II and separation in anaphase II fertilization

Which of these cells is (are) haploid? The figure shows the process of meiosis. Initially, chromosomes are scattered all over the cell. This stage is labeled A. During interphase, they become replicated and arranged in pairs with homologous chromosomes. This stage is labeled B. During meiosis 1, which is labeled C, the cell divides into 2 and each cell has 1 chromosome. During meiosis 2, which is labeled D, the cells from meiosis 1 divide into 2 once again. The resulting cells all have 1 chromatid.

C and D (Once meiosis I is completed, cells are haploid.)

The levels of pituitary hormones never increase above 10 grams/L of blood.

Cannot be determined from the graph

Which statement correctly describes how cellular DNA content and ploidy levels change during meiosis I and meiosis II?

DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II. (During anaphase of both meiosis I and meiosis II, the DNA content (number of copies of chromosomes) in a cell is halved. However, the ploidy level changes only when the number of unique chromosome sets in the cell changes. This occurs only in meiosis I (where separation of homologous chromosomes decreases the ploidy level from 2n to n and produces daughter cells with a single chromosome set).)

Which of the following events occurs at the onset of the luteal phase of the menstrual cycle?

Development of the corpus luteum. (The corpus luteum develops from the ruptured follicle during the luteal phase after ovulation.)

How does spermatogenesis differ from oogenesis?

Diploid cells give rise to four functional gametes in spermatogenesis.

__________ stimulates the development of ovarian follicles.

FSH

Which pituitary secretion stimulates sperm production?

FSH (In males, follicle-stimulating hormone (FSH) stimulates sperm production.)

Identify the role(s) of follicle-stimulating hormone (FSH) in human reproduction. Select all that apply.

FSH stimulates the growth of new follicles in the ovary. FSH promotes the activity of Sertoli cells, which nourish sperm developing within seminiferous tubules.

True or false? The production of sperm begins at puberty when spermatogonia undergo meiosis I to form primary spermatocytes, which then undergo meiosis II to form secondary spermatocytes. These secondary spermatocytes go on to form spermatids, which mature into sperm cells.

False (Spermatogonia divide by mitosis and differentiate into primary spermatocytes. Starting at puberty, hormones stimulate the primary spermatocytes to undergo meiosis I to form secondary spermatocytes, which then undergo meiosis II to form spermatids.)

What products are formed when a diploid cell undergoes meiosis?

Four haploid cells.

Cells will usually divide if they receive the proper signal at a checkpoint in which phase of the cell cycle?

G1 (In mammalian cells, this checkpoint is termed the restriction point.)

Select the statement that accurately describes gametes.

Gametes, such as eggs and sperm, are haploid reproductive cells that fuse during fertilization in sexual life cycles.

Which of these is true of the cytoplasm of an unfertilized egg?

It is an unevenly distributed mixture of mRNA, proteins, organelles, and other substances. (Many proteins are found concentrated at one end of the cell or another and provide positional information to the developing embryo.)

An increase in ________ concentration triggers ovulation.

LH

Which pituitary secretion stimulates the testes to secrete androgens?

LH (In males, luteinizing hormone (LH) stimulates the testes to secrete androgens.)

A surge in which hormone(s) immediately precedes ovulation?

LH and FSH

Which hormone spikes midway through the menstrual cycle and triggers ovulation?

Luteinizing hormone (LH). (Luteinizing hormone (LH) secreted by the pituitary gland causes the mature ovarian follicle to rupture, a process called ovulation.)

A surge in estradiol levels correlates with a surge in progesterone levels.

Not supported

Which hormone's secretion is controlled by a positive feedback mechanism?

Oxytocin

Which characteristic of the male reproductive system is not variable among animal species that reproduce sexually?

Presence of genitalia.

Which function is not performed by the male reproductive system?

Production and storage of oogonia. (Oogonia are produced bythe female reproductive system.)

All your cells contain proto-oncogenes, which can change into cancer-causing genes. Why do cells possess such potential time bombs?

Proto-oncogenes are necessary for the normal control of cell growth and division. (Proto-oncogenes can become oncogenes when a mutation or other genetic change increases the activity of the encoded protein.)

Proto-oncogenes can change into oncogenes that cause cancer. Which of the following best explains the presence of these potential time bombs in eukaryotic cells?

Proto-oncogenes normally help regulate cell division.

Which diploid cells are produced by an embryonic germ cell?

Spermatogonia.

Which statement about human reproduction is false?

The earliest stages of spermatogenesis occur closest to the lumen of the seminiferous tubules. (Spermatogenesis and oogenesis require different temperatures. An oocyte completes meiosis after a sperm penetrates it. Fertilization occurs in the oviduct. Effective hormonal contraceptives are currently available only for females. Are all true)

Which of the following is a true statement?

The endometrial lining is shed in menstrual cycles but reabsorbed in estrous cycles

Which statements correctly explain how the hormone-based contraceptives affect the female reproductive cycle?

The progestin in the progestin-only pill causes changes in the endometrium that prevent implantation. The low doses of progestin and estradiol in the combination pill have a negative feedback effect on the hypothalamus, blocking ovulation. The low dose of estradiol in the combination pill prevents the surge in LH production.

Heredity.

The transmission of traits from parents to offspring

Assume that an organism exists in which crossing over does not occur, but that all other processes associated with meiosis occur normally. Consider how the absence of crossing over would affect the outcome of meiosis. If crossing over did not occur, which of the following statements about meiosis would be true? Select all that apply.

There would be less genetic variation among gametes.

What role do germ cells play in gametogenesis?

They produce cells that divide by mitosis and then undergo meiosis to form gametes.

Which of the following is true of benign tumors, but not malignant tumors?

They remain confined to their original site (They remain confined to their original site)

True or false? Humans form gametes by a process called gametogenesis.

True

True or false? The basic functions of the human female reproductive system are to produce eggs, develop offspring, and make hormones.

True (Eggs are produced in the ovaries and transported to the uterus, the site of embryonic development.)

Where does a human fetus develop?

Uterus. (The uterus is the site of implantation and embryonic development.)

Which male reproductive structures are responsible for the transport and delivery of sperm?

Vas deferens, urethra, and penis. (The vas deferens transports sperm from the epididymis to the ejaculatory duct, which empties into the urethra; the urethra carries sperm through the penis to the outside of the body and into the female reproductive tract.)

Chromosomes are duplicated and lined up by homologous pair _________________.

at the start of meiosis I

What structure is where sister chromatids are joined together?

centromere (The centromere is the point of attachment between two sister chromatids of a duplicated chromosome.)

The junction of the upper vagina and the uterus is called the

cervix

Which processes lead to most genetic variation in sexually reproducing organisms? Select all that apply.

crossing over independent assortment of chromosomes in meiosis random fertilization

Secondary Sex Characteristics of Males

deep voice, male hair growth pattern, increased muscle size, increased aggressiveness

Secondary Sex Characteristics of Females

enlarged breasts, fat deposition in hips and breasts, water retention, changes in calcium metabolism and bone deposition

Sperm become capable of movement while in the _____.

epididymis

A peak in _______________ levels causes a surge in LH secretion, leading to ovulation.

estradiol

Based on the graph, elevated levels of which hormone(s) most likely stimulate the LH/FSH surge just before ovulation?

estradiol

If there is no fertilization, degeneration of the corpus luteum results in a drop in _____, which results in the sloughing off of the uterus's endometrium.

estrogen and progesterone (Estrogen and progesterone are responsible for maintaining the endometrium in the event that the egg has been fertilized.)

After ovulation, high levels of _____ inhibit _____ secretion.

estrogen and progesterone ... FSH and LH

Developing ovarian follicles primarily secrete _____.

estrogens

_____ is a carcinogen that promotes colon cancer.

fat (A diet high in fat increases the risk of both colon and breast cancer.)

Which of these is NOT a carcinogen?

fat testosterone cigarette smoke UV light all of the above are carcinogens