BIO156 - Chapter 8 (Mastering Biology)

Identify the stages of the cell cycle

1. Interphase 2. Prophase 3. Metaphase 4. Anaphase 5. Telophase

Normal human gametes carry _____ chromosomes.

23

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

2^23 (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.)

Polyploidy is involved in which of the following examples? A) XYY males B) XO females C) A normal watermelon has 22 chromosomes but seedless watermelons have 33 chromosomes. D) Some plants alternate between haploid and diploid phases.

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

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

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

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.

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

Crossing over (Crossing over, the exchange of corresponding segments between nonsister chromatids of homologous chromosomes, only occurs during meiosis.)

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.

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

Prophase

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

The correct order of events during meiosis is

Prophase I Metaphase I Anaphase I Telophase I Cytokinesis Meiosis II.

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.

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.

Chromatids are _____________.

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

During anaphase II, __________.

sister chromatids separate and migrate toward opposite poles

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

16

During anaphase I, __________.

homologous chromosomes separate and migrate toward opposite poles

During prophase I of meiosis,

homologous chromosomes stick together in pairs.

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 (Cytokinesis in plant cells would be blocked because the cell plate that ultimately separates one cell into two is formed from coalescing vesicles.)

Meiosis starts with a single diploid cell and produces

Four haploid cells

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

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 (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.)

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. (Trisomy means three copies of a chromosome; duplication involves a repeated segment of one chromosome.)

A cell preparing to undergo meiosis duplicates its chromosomes during

Interphase

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. (The separation of the duplicating chromosomes ensures that each daughter cell receives a chromosome.)

Gametes are produced by _________.

Meiosis

Variation occurs when chromosomes are shuffled in _____.

Meiosis (Variation is produced as a result of independent assortment and crossing over.)

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

its cells each have one set of chromosomes