Biology Exam 3

Which of the following occurs in meiosis I but not meiosis II?

-Diploid daughter cells are produced. -Chromosomes without sister chromatid arrangement line up along the metaphase plate. -Centromeres divide. ****-Crossing over (recombination) occurs. -The spindle apparatus (centrosomes + microtubules) forms.

The first step of bacterial replication is

DNA replication

True or False: Cytokinesis always occurs immediately following the events of mitosis to produce two cells and meiosis to produce four cells.

False

True or False: The process of binary fisson produces two genetically identical cells in a process that requires prophase, metaphase, anaphase, telophase and cytokinesis.

False

Which of the following phases does the average cell spend the most time in?

Interphase

What is a key difference between meiosis and mitosis?

Synapsis (the pairing of homologous chromosomes) occurs only in meiosis (prophase I).

Cytokinesis often, but not always, accompanies

Telophase

Which of the following statements regarding genetic diversity is false?

-Genetic diversity is enhanced by random fertilization of gametes. -Genetic diversity is enhanced by random alignment of homologous pairs at Metaphase I. -Genetic diversity is enhanced by crossing over (recombination) during Prophase I. ****-Genetic diversity is enhanced by mitosis in somatic cells.

Gametes differ from somatic cells in what ways?

-They have one member of each pair of homologous chromosomes -They are haploid -They function in sexual reproduction -They have one half of the genetic material

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

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

Benign tumors do not metastasize; malignant tumors do.

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.

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

Cytokinesis

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

False. M phase is shorter than interphase; cells spend most of their time in interphase.

An organism has a haploid chromosome number n = 4. How many tetrads will form during meiosis?

Four. (Because of the synapsis of homologous chromosomes, the number of tetrads in meiosis will be the same as the haploid number of chromosomes.)

Cells will usually divide if they receive the proper signal at a checkpoint in the _____ phase of the cell cycle.

G1

Why is crossing over important?

It allows the exchange of genes between homologous chromosomes. (combining DNA from two parents into a single chromosome allows for genetic variation.)

At which stage of mitosis are chromosomes lined up in one plane in preparation for their separation to opposite poles of the cell?

Metaphase

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

Metaphase (Occurs in the MIDDLE of mitosis)

After fertilization, the resulting zygote begins to divide by what process?

Mitosis. Zygotes are somatic cells.

Spindle fibers attach to kinetochores during

Prometaphase

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

Prophase

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

Prophase

Chromosomes become visible during

Prophase, the chromatin fibers become discrete chromosomes

The exchange of parts between nonhomologous chromosomes is called

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

How do asexual and sexual reproduction differ?

Sexual reproduction can produce great variation among the offspring, whereas asexual cannot.

An example of a cell that is 2n is a ______ cell?

Somatic (referring to the body). These cells are diploid and have **two homologous copies of each chromosome.

At a critical point in meiosis, the chromosomes do not replicate. This occurs between what two phases?

Telophase I and prophase II. (If DNA were to replicate at this phase, then the cell would still be haploid, but it would contain an abnormal number of chromosomes.)

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

Telophase, the final phase of 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?

The chromosome number in both cases would be normal, but in trisomy there would be three chromatids on one chromosome and in a duplication there would be two chromatids on one chromosome. (Trisomy means three copies of a chromosome)

What must happen before a cell can begin mitosis?

The chromosomes must be duplicated, which occurs during interphase.

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.

As a patch of scraped skin heals, the cells fill in the injured area but do not grow beyond that. This is an example of

density-dependent inhibition.

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

four ... haploid

Meiosis starts with a single diploid cell and produces

four haploid cells

During prophase I of meiosis,

homologous chromosomes stick together in pairs.

Two chromosomes in a nucleus that carry genes controlling the same inherited characteristics are

homologous chromosomes.

A cell preparing to undergo meiosis duplicates its chromosomes during what phase?

interphase

Nucleoli are present during

interphase

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 "multinucleated"

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

metaphase II

Synapsis occurs 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.

During _____ a spindle forms in a haploid cell.

prophase II

Which of the following is not a property of a malignant cancer cell?

stimulates angiogenesis ignores cell cycle checkpoints *is considered totipotent is immortal has lost density dependence

What body/cellular functions does not typically involve some type of cell division?

synthesis of ATP

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

telophase I

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

telophase II

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

Individual chromosomes are usually observed with a light microscope during mitosis, even though cells spend more time in interphase. This is because _____.

they have uncoiled to form long, thin strands

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

two ... haploid

During prophase a homologous pair of chromosomes consists of

two chromosomes and four chromatids

Mitosis produces _______(how many) cell(s) that are that are _________(genetically identical/different).

two, genetically identical

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. Each chromosome (12) is replicated, there are 24 DNA molecules in the nucleus during G2 phase.

If a cell had 22 chromosomes at the end of mitosis, how many will it have at the end of the next S Phase?

44

A human bone marrow cell, in prophase of mitosis, contains 46 chromosomes. There are _____ chromatids.

92

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 growth factors are present A check that the cell is large enough for division A check that nutrients are sufficient *A check that chromosome replication has been successfully completed (Chromosome replication does not occur until after G1; this checkpoint is a G2 checkpoint.)

The M-phase checkpoint in mitosis determines whether sister chromatids have divided properly and there is the proper amount of DNA on each side of the dividing cell. Specifically, we would predict that this checkpoint occurs in

Anaphase

The phase of mitosis during which the chromosomes move toward separate poles of the cell is

Anaphase

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

Anaphase

Centromeres divide and sister chromosomes become full-fledged chromosomes during

Anaphase, sister chromatids separate and migrate to opposite poles

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.

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. 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

Homologous chromosomes migrate to opposite poles during _____.

anaphase I

During _____ sister chromatids separate.

anaphase II

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

Bacteria divide by:

binary fission