Chapter 8 Mastering

Gametes are produced by _____.

Meiosis Explanation: Meiosis produces haploid gametes from a diploid parental cell.

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

16

Normal human gametes carry _____ chromosomes.

23 Explanation: This is the number of chromosomes in a single set of human chromosomes.

In humans, the haploid number of chromosomes is 23. Independent assortment has the possibility of producing __________ different gametes.

2^23 Explanation: For each gamete, there are two possibilities for each chromosome (the paternal or the maternal chromosome), and there are 23 different chromosomes per gamete. Crossing over can increase this number even further.

On average, what percentage of infants born to 45-year-old mothers have Down syndrome?

30%

Meiosis starts with a single diploid cell and produces

4 haploid cells Explanation: Meiosis produces four haploid cells.

What is the difference between a benign tumor and a malignant tumor?

Benign tumors do not metastasize; malignant tumors do. Explanation: Malignant tumors spread from their site of origin to other parts of the body.

Which of these cells is (are) haploid?

C and D Explanation: Once meiosis I is completed, cells are haploid.

In the laboratory, cancer cells fail to show density-dependent inhibition of growth in cell culture. What is one explanation that could account for this?

Cancer cells continuously secrete growth factors into the cell culture medium. Explanation: In this case, the cells would stimulate their own growth and grow far more extensively than normal cells dependent on the limiting amounts of growth factor present in the medium.

Use the graph and your knowledge of Down syndrome to select the three true statements.

Down syndrome is caused by a trisomy of chromosome 21. The risk of having a baby with Down syndrome more than doubles for 45-year old mothers compared to 40-year old mothers. The incidence of Down syndrome in infants born to mothers under the age of 35 is less than 0.5%.

When examining cells in the laboratory, you notice that a particular cell has half as much DNA as the surrounding cells. This observation can be explained if this cell's cell cycle halted at checkpoint _____.

G1 Explanation: The cell cycle must have stopped before the S phase; otherwise, the cell would also have twice as much DNA.

You suspect that a serious developmental disorder is due to a chromosome abnormality and prepare a karyotype from an affected individual. In analyzing the karyotype, how could you distinguish trisomy from a chromosome structural defect such as a duplication?

In trisomy there would be one extra chromosome; in a duplication, the number of chromosomes would be normal, but one chromosome would have two copies of a portion of the chromosome.

During binary fission, each copy of the duplicating chromosome moves to opposite ends of the cell. What does this achieve?

It ensures that each daughter cell receives one copy of the chromosome. Explanation: The separation of the duplicating chromosomes ensures that each daughter cell receives a chromosome.

Drag the labels onto the diagram to identify the stages of the cell cycle.

Most of the cell's life is spent in interphase, when growth occurs. Cells are about to divide and replicate their DNA In prophase microtubules form the mitotic spindle, and the nuclear envelop breaks up At metaphase, the mitotic spindle is fully formed and chromosomes are lined up in the center of the cell In anaphase, sister chromatids separate and becomes full-fledged chromosomes that move to opposite poles In telophase, chromosomes become less intense and new nuclear envelop forms. In cytokinesis, the cytoplasm divides

Trisomy for most autosomes is fatal, yet trisomy or even tetrasomy (four copies) of the X chromosome is not. What is the explanation for this difference?

Only one copy of the X chromosome is functional within any given cell, regardless of the total number of X chromosomes. Explanation: This is the reason that alterations in the number of X chromosomes are much better tolerated than autosomal trisomy.

In the telophase of mitosis, the mitotic spindle breaks down and the chromatin uncoils. This is essentially the opposite of what happens in _____.

Prophase Explanation: During prophase we observe the formation of the spindle, the condensation of chromatin, and the disappearance of the nucleolus, which are the opposite events to those occurring during telophase.

Although in humans there are 22 pairs of autosomal chromosomes, only three different chromosomal trisomies are commonly seen in newborns. Of the remaining 19 autosomes, many trisomies have not been seen in newborns. Why not?

Trisomy for the other autosomal chromosomes is often lethal, and the affected embryos are miscarried.

Drag the terms to complete the concept map below.

a. diploid organisms b. haploid gametes c. meiosis II d. maternal chromosomes e. crossing over occurs f. sister chromatid separate

Drag the labels onto the diagram to identify the stages of the life cycle. Not all labels will be used.

a. gametes b. haploid c. meiosis d. fertilization e. diploid f. zygote g. mitosis

Drag the labels to the correct locations on these images of human chromosomes.

a. homologous chromosome b. centromere c. sister chromatids d. autosomes e. sex chromosomes f. karyotype

Drag the labels onto the grid to indicate the phases of mitosis and meiosis. Use only pink labels for pink targets.

a. mitosis b. prophase c. metaphase d. anaphase, telophase, and cytokinesis e. meiosis f. prophase I g. metaphase I h. anaphase I, telophase I, and cytokinesis i. meiosis II

Drag the labels onto the diagram to identify the various chromosome structures.

a. pair of homologous chromosomes b. centromere c. sister chromatids

What name is given to this process?

asexual reproduction Explanation: A single individual is reproducing.

Meiosis differs from mitosis in that _____ only occurs in meiosis.

crossing over Explanation: Crossing over, the exchange of corresponding segments between nonsister chromatids of homologous chromosomes, only occurs during meiosis.

A cell is treated with a drug that prevents the formation of vesicles. Which of the following processes depends on the formation of vesicles and would therefore be blocked?

cytokinesis in a plant cell Explanation: Cytokinesis in plant cells would be blocked because the cell plate that ultimately separates one cell into two is formed from coalescing vesicles.

Consider the photograph shown below. You can determine this is a plant cell rather than an animal cell because it has __________.

formed a cell plate Explanation: The cell plate, which divides the cytoplasm in two, forms during telophase of mitosis in a plant cell and can be observed in the center of this image.

During anaphase I, __________.

homologous chromosomes separate and migrate toward opposite poles

During prophase I of meiosis,

homologous chromosomes stick together in pairs.

Chromatids are _____.

identical copies of each other if they are part of the same chromosome Explanation: Each duplicated chromosome consists of two identical sister chromatids.

A cell preparing to undergo meiosis duplicates its chromosomes during

interphase

When we say that an organism is haploid, we mean that _____.

its cells each have one set of chromosomes Explanation: A cell with a single chromosome set is called a haploid cell. Organisms with this type of cells are haploid organisms.

Variation occurs when chromosomes are shuffled in _____.

meiosis Explanation: Variation is produced as a result of independent assortment and crossing over.

The correct order of events during meiosis is

prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II. Explanation: Meiosis starts with prophase I and continues with metaphase I, anaphase I, telophase I, and cytokinesis. This is followed by meiosis II.

During meiosis, segments of nonsister chromatids can trade places. This recombination of maternal and paternal genetic material is a key feature of meiosis. During what phase of meiosis does recombination occur?

prophase I.

During anaphase II, __________.

sister chromatids separate and migrate toward opposite poles

Polyploidy is involved in which of the following examples?

A normal watermelon has 22 chromosomes but seedless watermelons have 33 chromosomes. Explanation: Seedless watermelons have acquired an entire extra set of chromosomes, which makes them polyploid.

Immune system cells enter a resting phase after undergoing mitosis. When activated—for example, by an infection—they can reenter the sequence of events in the cell cycle that leads to cell division. What would be the correct cell cycle sequence of events for these reactivated cells?

G1, S, G2, M Explanation: After reactivation, these cells move into G1. Here they grow in preparation for DNA replication (S phase). Once complete, the cells move into G2 and make the final preparations for mitosis.

In theory, when a nondisjunction for chromosome 18 occurs during meiosis I, four gametes can be produced. If these gametes are fertilized with unaffected gametes from the second parent, what observations would you make concerning the resulting embryos?

Two of the embryos will be trisomic for chromosome 18, and two will contain a single copy of chromosome 18. Explanation: A nondisjunction that occurs in the first meiotic division will result in one daughter cell having two copies of chromosome 18. This will be trisomic upon fertilization. The other daughter cell will have no copies of chromosome 18 and will contain a single copy of chromosome 18 upon fertilization, a condition known as monosomy.

Consider the photograph of a karyotype. This is _____.

a photograph of all a person's chromosomes Explanation: Karyotypes, ordered displays of a person's chromosomes, are useful in identifying chromosomal abnormalities.