mastering bio chapter 8

Which processes lead to most genetic variation in sexually reproducing organisms?

1. crossing over 2. independent orientation of chromosomes in meiosis 3. random fertilization

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.

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

16; 16 is half of 32.

Normal human gametes carry _____ chromosomes.

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

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.

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.

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

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

Assign a numerical score for each category. Then add up the total score. (The highest possible score is 6; the lowest is 0.) In what range does this source fall?

5 to 6

Which of the following patients is currently most likely to benefit from immunotherapy?

A 46 year old woman with advanced melanoma.

Which of the following people most likely got cancer because of environmental factors?

A 47-year-old woman with lung cancer.

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.

What is IGF-II?

A chemical that stimulates growth in pancreatic tumors.

Polyploidy is involved in which of the following examples?

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.

According to this research, a pancreatic cancer patient with which of the following would likely fair the best?

A patient with a large number of cheater cells.

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

Anaphase

Which of these gametes contains one or more recombinant chromosomes?

B and C; Each of the chromosomes in gametes B and C are composed of material derived from both parents.

Which of these cells is (are) haploid?

C and D; 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; 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.

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.

Which of the following statements correctly describes the timing of DNA synthesis?

DNA is synthesized in the S phase of interphase; Single chromosomes enter the synthesis or S phase of interphase. At the end of this phase, after DNA replication, the chromosomes are double, each consisting of two sister chromatids.

The first step of bacterial replication is _____.

DNA replication; The DNA must be copied in order to proceed

Which of the following is an example of a lifestyle factor?

Diet

Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16?

Extra copies of the other somatic chromosomes are probably fatal; Except for trisomy 21, somatic trisomies are almost always lethal.

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.

Which of the following will have authorization to decide if and when CAR can be used?

Food and Drug Administration

You are the CEO of pharmaceutical company Merck. Your company has a new cancer drug it wishes to introduce to the market. Who do you need approval from?

Food and Drug Administration

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.

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.

Acceding to this research, which of the following is in the correct order for cause of mutation leading to cancer from least likely to most likely?

Heredity, environment, random error

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.

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.

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.

The likelihood of death within twenty years of a diagnosis for DCIS (ductal carcinoma in situ, a type of breast cancer) is only 3.3%. Does this mean that every individual diagnosed with DCIS has a 3.3% chance of death within twenty years from the disease?

No. Individuals within certain risk groups (such as women under age 40) have a risk notably higher than 3.3%, whereas individuals not in these risk groups have a lower risk on average; Black women and women diagnosed before age 40 have a notably higher risk of death than those not in these risk groups.

If this research holds true, which of the following would happen in treatment?

Non-producing cells would cause the destruction of a tumor.

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; This is the reason that alterations in the number of X chromosomes are much better tolerated than autosomal trisomy.

A

Pair of homologous chromosomes

You are an oncologist doing research that confirmed what was known about producer/cheater relationships in pancreatic tumors. What did you find out?

Producers get nothing from cheaters.

Cancer is characterized by mutations that do what?

Promote abnormal cell growth and division.

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.

C

Sister chromatids

Which of the following is a key difference between meiosis and mitosis?

Synapsis occurs; The pairing of homologous chromosomes during prophase I of meiosis is called synapsis.

The success of cell therapy to treat cancer relies on which of the following?

T-cells

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.

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 mitotic spindle forms from microtubules that extend from the centrosomes.

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. Only during meiosis I do the homologous chromosomes pair up and then cross over.

What do you find in the References list at the bottom of the page?

The references are all from primary sources.

If CAR is approved, which of the following will be true?

The treatment will be tailor-made for each patient.

Which of the following is a hallmark of cancer cells?

They multiply quickly.

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; Unfortunately, these trisomies do occur and are commonly observed in spontaneously aborted embryos and fetuses.

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.

Which of the following is true?

Using more than one immunotherapy drug typically increases survival length.

According to this research, which of the following is true?

When it comes to cancer, developed countries are very similar to developing countries.

Which of the following indicates Turner syndrome?

XO; This is the sex chromosome complement of an individual with Turner syndrome.

Which of the following represents a chromosomally normal human female?

XX

Is the information provided by these sites consistent with what you found on the Skin Cancer Foundation web site?

Yes, other sites corroborate the information on the Skin Cancer Foundation site.

What is different concerning the DNA in bacterial cells as opposed to eukaryotic cells?

all of the above are differences between prokaryotic and eukaryotic DNA

Crossing over is important because it __________.

allows the exchange of different versions of genes between homologous chromosomes; Crossing over, by combining DNA from two parents into a single chromosome, is an important source of genetic variation in sexual life cycles.

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

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.

During _____ sister chromatids separate.

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

The stage of mitosis during which the chromosomes move toward separate poles of the cell is _____.

anaphase; Anaphase begins when the paired centromeres of each chromosome separate, liberating the sister chromatids. These are now considered individual chromosomes and begin moving toward opposite poles of the cell.

Centromeres divide and sister chromatids become full-fledged chromosomes during _____.

anaphase; During anaphase, sister chromatids separate and migrate to opposite poles.

What name is given to this process?

asexual reproduction; A single individual is reproducing.

A cell replicates its entire chromosomal DNA only __________.

before it is about to divide; This ensures that genetic material can be appropriately distributed to each of the daughter cells.

Bacteria divide by:

binary fission

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.

Your cousin has been added to a clinical trial for CAR. Which of the following will be a precursor to prepare him for this treatment?

chemotherapy

Your aunt is prescribed the new immunotherapy drugs for her cancer. Which of the following side effects is she most likely to experience?

colitis

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.

In bacterial cells, binary fission involves __________.

distribution of a copy of the single parental chromosome to each daughter cell

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; 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.

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

four ... haploid; At the end of meiosis II there are typically 4 haploid cells.

The function of meiosis is to make __________.

four cells with a haploid number of chromosomes; The two cell divisions of meiosis, I and II, produce four haploid daughter cells, which are not genetically identical to the diploid parent cell.

Meiosis starts with a single diploid cell and produces

four haploid cells

What is the typical result when a diploid cell undergoes meiosis?

four haploid cells; The two cell divisions of meiosis, I and II, produce four haploid daughter cells, which are not genetically identical to the diploid parent cell.

During asexual reproduction, yeast cells can produce _____.

genetically identical offspring; Asexual reproduction produces genetically identical offspring.

Fertilization joins _____ to produce a _____.

haploid gametes ... diploid zygote

During anaphase I, __________.

homologous chromosomes separate and migrate toward opposite poles; Homologous chromosomes do separate during anaphase I of meiosis.

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; Each duplicated chromosome consists of two identical sister chromatids.

A cell preparing to undergo meiosis duplicates its chromosomes during

interphase

Nucleoli are present during _____.

interphase

A fragment of chromosome 21 reattaches to chromosome 21, but in the reverse direction. What is the name given to this change?

inversion An inversion occurs when a fragment reattaches to the original chromosome but in the reverse direction. Usually, these aberrations result in fewer harmful effects than other chromosomal alterations as the genes are still present in their normal number.

In some organisms such as certain fungi and algae, cells undergo mitosis repeatedly without subsequently undergoing cytokinesis. What would be the consequence of this?

large cells containing many nuclei; The term for this type of cell is "multinucleated."

A patient with which of the following would be most likely to be successfully treated with CAR-T cell therapy?

leukemia

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

meiosis

Gametes are produced by _____.

meiosis; Meiosis produces haploid gametes from a diploid parental cell.

Variation occurs when chromosomes are shuffled in _____.

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

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

metaphase II; Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid.

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, independent of its homolog. You are witnessing _____.

metaphase of mitosis

Which of the following is a correct representation of an event that occurs in mitosis?

metaphase—chromosomes line up on the equatorial plane; In metaphase, the chromosomes line up along an imaginary midline, which is equidistant between the two poles of the spindle.

After fertilization, the resulting zygote begins to divide by __________.

mitosis; Mitosis ensures that all somatic cells receive copies of the parental chromosomes.

During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____.

nondisjunction; In nondisjunction, chromosomes fail to separate properly at meiosis.

Duplication of the chromosomes to produce sister chromatids _____.

occurs in both mitosis and meiosis

The term binary fission is best applied to _____.

prokaryotes

Spindle fibers attach to kinetochores during _____.

prometaphase

Synapsis occurs during _____.

prophase I Synapsis is the pairing of homologous chromosomes during prophase I.

The correct order of events during meiosis is

prophase I, metaphase I, anaphase I, telophase I, cytokinesis, 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. Segments of nonsister chromatids trade places during prophase I, resulting in recombination.

Crossing over occurs during _____.

prophase I; During prophase I of meiosis, homologous chromosomes pair up and can exchange genetic information.

Synapsis occurs during _____.

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

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.

Chromosomes become visible during _____.

prophase; The chromatin fibers become discrete chromosomes.

Immunotherapy works by blocking actions of which of the following?

proteins

During anaphase II, __________.

sister chromatids separate and migrate toward opposite poles; This occurs during anaphase II of meiosis and during anaphase in mitosis.

An example of a cell that is 2n is a __________.

somatic cell; Somatic is a word used to refer to the "body." These body cells are diploid and have two homologous copies of each chromosome.

Mitosis occurs in _____; meiosis occurs in _____.

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

Cytokinesis often, but not always, accompanies _____.

telophase

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; At the end of telophase II and cytokinesis there are four haploid cells.

DNA replication occurs in _____.

the S phase of interphase; Chromosomes are duplicated only during the S phase. "S" stands for synthesis of DNA.

Crossing over is _____.

the exchange of homologous portions of nonsister chromatids; The result is new combinations of genetic material (genetic recombination).

What seems to be the main purpose of the article?

to summarize the data demonstrating the carcinogenic effects of UV radiation from indoor tanning

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

two ... haploid; At the end of meiosis I there are two haploid cells.

During prophase a homologous pair of chromosomes consists of _____.

two chromosomes and four chromatids; At this point each of the chromosomes consists of two 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.

Homologous chromosomes possess the same genes arranged in the same order but may possess different __________ of some of these genes.

versions

In a cell containing 10 chromosomes, meiosis results in the formation of daughter cells containing __________ chromosomes.

5; Haploid gamete cells contain half as many chromosomes as diploid somatic cells.

B

Centromere

What is the affiliation of the writer?

The author is a medical doctor who serves leadership roles for cancer research and prevention organizations.

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.

Consider the photograph of a karyotype. This is _____.

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

The exchange of parts between nonhomologous chromosomes is called _____.

reciprocal translocation Reciprocal translocation is the exchange of genetic material between nonhomologous chromosomes.