Mastering Bio Chapter 8

Cytokinesis often, but not always, accompanies

telophase

During _____ sister chromatids separate.

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

Meiosis starts with a single diploid cell and produces

four haploid cells.

During prophase I of meiosis,

homologous chromosomes stick together in pairs.

Spindle fibers attach to kinetochores during

prometaphase

Chromosomes become visible during

prophase

The correct order of events during meiosis is

prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II.

During _____ a spindle forms in a haploid cell.

prophase II Prophase II is essentially the same as mitotic prophase except that the cells are haploid.

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

two ... haploid

Mitosis occurs in _____; meiosis occurs in _____.

somatic or body cells ... germ cells in the testes or ovaries

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.

The chromosomes arrive at the poles and nuclear envelopes form during which phase of mitosis?

Telophase Telophase is the final phase of mitosis, when the chromosomes have arrived at the poles and the nuclear envelopes of the two new cells form.

Asexual and sexual reproduction differ in that sexual reproduction

can produce great variation among the offspring As long as there is some genetic variation in the parents, different offspring will inherit unique combinations of genes from each parent, creating variation among offspring.

A cell biologist carefully measured the quantity of DNA in grasshopper cells growing in cell culture. Cells examined during the G2 phase of the cell cycle contained 200 units of DNA. What would be the amount of DNA in one of the grasshopper daughter cells?

100 units. Recall that G2 follows S, and that during the S phase, DNA is replicated. Then, chromatids are separated during mitosis to form daughter cells.

Baker's yeast is an organism with 32 chromosomes that can perform asexual or sexual reproduction and exist as both a diploid and haploid cell. After meiosis, how many chromosomes will be present in each cell?

16 (During sexual reproduction, meiosis reduces chromosome number by one-half, or to 16 in the case of yeast. This is because each chromosome is paired in a diploid cell and meiosis produces four haploid cells.)

A certain species of animal has six pairs of chromosomes. How many DNA molecules are present in the nuclei of these animals during G2 phase?

24. DNA replication is completed during S phase, which occurs prior to G2 phase. Since each chromosome (12) is replicated, there are 24 DNA molecules in the nucleus during G2 phase.

Each somatic cell in an individual with Down syndrome contains _____ chromosomes.

47 (Down syndrome is the result of having three copies of chromosome 21.)

A human bone marrow cell in the prophase stage of mitosis contains 46 chromosomes. Therefore, there are a total of __________ sister chromatids in this cell.

92

Which of the following checkpoints does not occur late in G1?

A check that chromosome replication has been successfully completed (Chromosome replication does not occur until after G1; this checkpoint is a G2 checkpoint).

The sister chromatids separate and begin moving toward opposite poles of the cell during which phase of mitosis?

Anaphase Sister chromatids separate and start their migration toward opposite poles during anaphase.

True or false. Mitosis takes place during M phase of the cell cycle, which is longer than interphase.

False. Mitosis does indeed take place during M phase, but M phase is shorter than interphase; cells spend most of their time in interphase.

When examining cells in the laboratory, you notice that a particular cell has half as much DNA as the surrounding cells. It appears that 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, 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

Nuclei are present during

Interphase

The chromosomes line up in the center of the cell during which phase of mitosis?

Metaphase Metaphase occurs in the middle of mitosis, when the chromosomes line up in the middle of the cell.

___ is the spread of cancer cells from their site of origin to other sites in the body.

Metastasis

The centrosomes move away from each other and the nuclear envelope breaks up during which phase of mitosis?

Prophase Prophase is the first phase of mitosis, when the centrosomes begin moving toward opposite poles and the nuclear envelope breaks up.

What must happen before a cell can begin mitosis?

The chromosomes must be duplicated. Before mitosis can begin, the chromosomes, or genetic material, must be copied, which occurs during interphase.

What would be the immediate consequence of destroying a cell's centrosomes?

The mitotic spindle would not form.

The M phase of mitosis and M phase of meiosis both occur after interphase. However, the two processes differ in the arrangement and behavior of their chromosomes. How?

The pairing up of homologous chromosomes and crossing over only occur during meiosis.

Within one chromosome, what is the relationship between the sequence of bases in DNA of one sister chromatid compared to the other?

The sequences are identical. Except for the occurrence of rare mutations, this is always the case. Both sister chromatids come from replication of a single DNA molecule, which is present in the one chromatid before replication.

During meiosis I, homologous chromosomes form a tetrad. What does this accomplish?

This brings the chromosomes into alignment so that crossing over can create new combinations of genes present on a single chromosome. (Crossing over does this by exchange of corresponding parts between homologous chromosomes, creating a patchwork of maternal and paternal chromosome segments along a single chromosome.)

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. (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.)

If a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction, the resulting chromosomal abnormality is called _____.

an inversion

Centromeres divide and sister chromatids become full-fledged chromosomes during

anaphase

Homologous chromosomes migrate to opposite poles during _____.

anaphase I During anaphase I sister chromatids remain attached at their centromeres, and homologous chromosomes move to opposite poles.

In many organisms, including humans, chromosomes are found in homologous pairs. Homologous chromosomes _____.

are identical in the arrangement of their genes, but some versions of the genes may differ between the chromosomes (are identical in the arrangement of their genes, but some versions of the genes may differ between the chromosomes )

A______ is a lump of abnormal cells that, although growing out of control, remains at its original site.

benign tumor

An individual with a malignant tumor is said to have ___

cancer

The most common type of cancer is a ____; this type always originates in tissues that line organs.

carcinoma

A benign and a malignant tumor differ in that

cells of a benign tumor remain within the tumor, whereas cells of a malignant tumor can spread to other body tissues

At the end of the mitotic (M) phase, the cytoplasm divides in a process called

cytokinesis. Cytokinesis is the division of the cytoplasm that occurs in conjunction with telophase, the last phase in mitosis.

When forming buds, hydras

divide by mitosis. A hydra is a tiny multicellular animal that reproduces by sexual or asexual means. The bud cells in the hydra divide by mitosis, and eventually the offspring will detach from the parent. The offspring will be genetically identical to the parent.

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

four ... haploid

Fertilization joins _____ to produce a _____.

haploid gametes ... diploid zygote

A____is an abnormally growing mass of cells that is actively spreading through the body.

malignant tumor

If it weren't for _____, chromosome number would double with every generation of sexual reproduction.

meiosis

Variation occurs when chromosomes are shuffled in _____.

meiosis

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

metaphase II

Looking through a light microscope at a cell undergoing division, you see that the condensed chromosomes have lined up along the midline of the cell. The homologous pairs are NOT joined in tetrads. Each chromosome takes its own place in line, independentof its homolog. You are witnessing _____.

metaphase of mitosis

Duplication of the chromosomes to produce sister chromatids _____.

occurs in both mitosis and meiosis

Synapsis occurs during _____.

prophase I Synapsis, the pairing of homologous chromosomes, occurs during prophase I.

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. (Segments of nonsister chromatids trade places during prophase I, resulting in recombination.)

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

telophase I At the end of telophase I and cytokinesis, there are two haploid cells with chromosomes that consist of two sister chromatids each.

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

telophase II

During mitosis, the chromosomes move because

they attach to a dynamic, precisely regulated mitotic spindle

In a cell with eight chromosomes, one chiasma develops during meiosis I in only one particular pair of homologs. How many recombinant chromosomes will there be at the completion of meiosis II?

two (This is because only two of the four chromatids present in a tetrad cross over at the chiasma. The other two chromatids do not exchange parts and are unaltered. Also, only one set of homologous chromosomes went through this process. )

During prophase a homologous pair of chromosomes consists of

two chromosomes and four chromatids

Mitosis and cytokinesis result in the formation of __________; meiosis and cytokinesis result in the formation of __________.

two diploid cells : four haploid cells In mitosis, a cell that has doubled its genetic material divides into two diploid daughter cells. In meiosis, a cell that has doubled its genetic material undergoes two rounds of division, resulting in the production of four haploid cells.