Chapter 8 Bio 1308

Which events occur during prophase?

-Chromosomes condense and are attached to spindle fibers. -The nuclear envelope breaks down.

In sexually reproducing multicellular organisms, the main functions of mitosis are _____.

-growth and development -tissue repair/replacement of damaged cells

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

-the amount of DNA present -whether the DNA is housed in a nucleus or not -whether the DNA is linear or circular all of the above are differences between prokaryotic and eukaryotic DNA

How many generations does it take to develop a new plant species by polyploidy?

1

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

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

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

Imagine that a human skin cell went through mitosis but did not undergo cytokinesis. How many chromosomes would be in the cell?

92 (When the cell prepared to divide, the chromosomes were replicated, and the chromosome number went from 46 to 92. Because these were not separated into daughter cells during cytokinesis, the cell still has 92 chromosomes.)

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.)

Polyploidy is involved in which of the following examples?

A normal watermelon has 22 chromosomes but seedless watermelons have 33 chromosomes.

Oncologists (medical doctors who treat cancer patients) routinely take biopsies (samples) of tissue from patients to determine whether the tissue is cancerous or not. What would be the best technique to use to determine whether cells from the tissue sample are cancerous?

Add cells from the tissue sample to a cell culture dish and compare their growth against a sample of noncancerous cells from the patient.

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

Anaphase

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.)

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.)

The first step of bacterial replication is _____.

DNA replication (The DNA must be copied in order to proceed)

Which of the following statements regarding Down syndrome is false?

Down syndrome is least likely to be seen in the infants of mothers over 40.

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.)

Chromosomes become visible during _____.

Prophase

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.)

Which of the following statements regarding sexual and asexual reproduction is true?

Sexual reproduction is more likely to increase genetic variation than is asexual reproduction.

Which of the following statements regarding mitosis and meiosis is true?

Sister chromatids separate during anaphase of mitosis and anaphase II of meiosis.

Cytokinesis often, but not always, accompanies _____.

Telophase

Looking through a light microscope at a dividing cell, you see two separate groups of chromosomes on opposite ends of the cell. New nuclear envelopes are taking shape around each group. The chromosomes then begin to disappear as they unwind. You are witnessing _____.

Telophase

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)

You have two flasks (labeled A and B) that each contain an equal population of normal animal cells. You place flask A in a machine called a shaking incubator, which shakes the flask at 37°C and keeps the cells moving so as to not allow them to adhere to the bottom of the flask. Flask B is allowed to sit in an incubator (without shaking) at 37°C. If you let the cells in each flask grow for a week, which of the following results are you most likely to observe?

The cells in flask B will have grown significantly, but the cells in flask A will have not grown at all.

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.)

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

benign tumor

Bacteria divide by:

binary fission

Karyotyping

can reveal alterations in chromosome number.

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.)

The process by which the cytoplasm of a eukaryotic cell divides to produce two cells is called

cytokinesis.

In bacterial cells, binary fission involves __________.

distribution of a copy of the single parental chromosome to each daughter cell (Prokaryotes reproduce by a type of cell division called binary fission, which involves replicating the single chromosome and distributing the copies equally to two daughter cells)

Cytokinesis _____.

finishes mitosis by dividing the cytoplasm and organelles of the original parent cell into two separate daughter cells

During asexual reproduction, yeast cells can produce _____.

genetically identical offspring (Asexual reproduction produces genetically identical offspring.)

At the conclusion of meiosis I, the daughter cells are _____.

haploid and the sister chromatids are joined (The daughter cells of meiosis I are haploid, and the sister chromatids are still joined. During meiosis II, the sister chromatids separate.)

At a chiasma, two ________ are attached to each other.

homologous or nonsister chromatids

During _____ the cell grows and replicates both its organelles and its chromosomes.

interphase (These are the events of interphase.)

If a chromosome fragment breaks off and then reattaches to the original chromosome but in the reverse direction, the resulting chromosomal abnormality is called a(n)

inversion.

Sister chromatids are

joined together at a centromere.

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

malignant tumor

Gametes are produced by _____.

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

Nondisjunction occurs when

members of a chromosome pair fail to separate.

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

nondisjunction

Down syndrome can be the result of _____.

nondisjunction of chromosome 21 during meiosis

A karyotype is most like

photographs of every couple at a high school prom.

Which of the following is probably the main factor responsible for the phenomenon of density-dependent inhibition?

physical contact of cell-surface proteins between adjacent cells

Independent orientation of chromosomes at metaphase I results in an increase in the number of

possible combinations of characteristics.

Asexual reproduction _____.

produces offspring genetically identical to the parent (Only one individual makes a genetic contribution to the offspring.)

The term binary fission is best applied to _____.

prokaryotes

Which of the following helps maintain the structure of chromosomes and control the activity of genes?

proteins

The exchange of parts between nonhomologous chromosomes is called _____.

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

One version of a gene may encode __________, whereas a different version of the same gene may encode __________.

red eyes; white eyes

Prior to mitosis and after S phase, each chromosome of a eukaryotic cell consists of a pair of identical structures called

sister chromatids.

During which phase of mitosis does the nuclear envelope re-form?

telophase

Cancer is not usually inherited because

the chromosomal changes in cancer are usually confined to somatic cells.

During _____ both the contents of the nucleus and the cytoplasm are divided.

the mitotic phase (The mitotic phase encompasses both mitosis and cytokinesis.)

During prophase a homologous pair of chromosomes consists of _____.

two chromosomes and four chromatids

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

versions

A cell replicates its entire chromosomal DNA only __________.

before it is about to divide

Which of the following conditions would prevent cell division due to density-dependent factors?

being completely surrounded by other cells

Spindle fibers attach to kinetochores during _____.

Prometaphase

A skin cell of a red fox has 34 chromosomes. You look at the cell under a microscope and see that it has 34 chromosomes and one nucleus. Several hours later, you look at the same cell again and see that it has double the amount of DNA and one nucleus. A little while later, you see that it has 68 chromosomes and two nuclei. What stage of the cell cycle was this cell in when you viewed it at each time point?

First view: G1; second view: G2; third view: telophase

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

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.)

Below are three statements. Classify them as examples of independent orientation, crossing over, or random fertilization. I: The formation of a zygote from an egg and a sperm is an unpredictable event. II: Random combinations of paternal and maternal chromosomes end up in gametes. III: An allele on the paternal chromosome 18 ends up on the maternal chromosome 18.

I: random fertilization; II: independent orientation; III: crossing over

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 _____, the cell carries out its normal functions and the chromosomes are thinly spread out throughout the nucleus.

Interphase

Nucleoli are present 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.)

Which of the following statements regarding mitosis and meiosis is false?

Meiosis provides for asexual reproduction.

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

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.

You are observing a single cell under a microscope. You go home for the night, and the next day you see four cells. The four cells look similar, and when you stain them with a dye that binds to DNA they all appear to contain the same amount of DNA as the original cell. What likely happened overnight?

The single cell divided to form two new cells, and the two new cells each divided to form four total cells, all by asexual reproduction.

During cell division, what role do centrosomes play?

They organize the microtubules.

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 comparing a frog cell in metaphase of mitosis with one in metaphase I of meiosis, how would tell you which was which?

Unlike mitosis, in meiosis each chromosome would be opposite its homolog

Which of the following variations of the sentence "Where is the cat?" is most like a chromosomal inversion?

Where the is cat?

Which of the following indicates Turner syndrome?

XO

You are asked to culture an unidentified sample of animal tissue. You notice that the cells seem to fail to exhibit density-dependent inhibition. The source of this tissue sample is most likely

a cancerous tumor.

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

Eukaryotic chromosomes differ from prokaryotic chromosomes in that they

are housed in a membrane-enclosed nucleus.