Biology Test 3 Part III

How many pairs of autosomes do humans have?

22 Humans have 22 pairs of autosomes and one pair of sex chromosomes.

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 2 possibilities for each chromosome and there are 23 different chromosomes per gamete) 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.

A human somatic cell contains __________ chromosomes.

46 Human somatic cells contain 22 pairs of autosomes and one pair of sex chromosomes.

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.

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 Mitosis follows the S phase, during which the cell's DNA is duplicated. Provide Feedback

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.

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 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. Black women and women diagnosed before age 40 have a notably higher risk of death than those not in these risk groups.

Crossing over occurs during _____.

Prophase 1 Crossing over that results in genetic recombination occurs during this phase.

During anaphase II

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

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.

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.

During cell division, what role do centrosomes play?

They organize the microtubules. The centrosomes are the microtubule-organizing centers of the cell.

Which of the following occurs during mitosis?

Two daughter nuclei, one at each pole of the cell, are generated. This is the purpose of mitosis.

Which of the following represents a chromosomally normal human female?

XX Human females are normally XX.

Crossing over is important because it __________.

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

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 nowconsidered individual chromosomes and begin moving toward opposite poles of the cell.

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.

Asexual and sexual reproduction differ in that sexual reproduction _____. View Available Hint(s)

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.

the chromosomal region where the nonsister chromatids are crossing over is called a(n) _____.

chiasma Chiasmata (plural of chiasma) are regions where crossing over has occurred.

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.

A cleavage furrow forms in an animal cell during _____.

cytokinesis In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two.

The diploid phase of the human life cycle begins with _____.

fertilization The union of haploid gametes at fertilization produces the zygote, or fertilized egg, which starts the diploid phase of the life cycle of humans and is characteristic of animals.

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.

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.

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.

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

In anaphase I, __________.

homologous chromosomes move toward opposite poles Meiosis I serves to separate homologous chromosomes so that each daughter cell ends up with just one set of chromosomes.

Chromatids are _____.

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

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

its cells each have one set of chromosomes A cell with a single chromosome set is called a haploid cell. Organisms with this type of cells are haploid organisms.

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."

Variation occurs when chromosomes are shuffled in _____.

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

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.

Asexual reproduction _____.

produces offspring genetically identical to the parent produces offspring genetically identical to the parent

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 prophase we observe the formation of the spindle, the condensation of chromatin, and the disappearance of the nucleolus, which are the opposite events to those occurring during telophase.

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 is the pairing of homologous chromosomes during prophase I.

Which of the following shows mitosis in the correct chronological order?

prophase, prometaphase, metaphase, anaphase, telophase Mitosis moves through these five phases in this order, separating out the replicated chromosomes into two new daughter cells.

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

red eyes; white eyes Different versions of a gene could encode different eye colors. Alternately, they could encode different coat colors.

In meiosis II, _____.

sister chromatids are separated This is the task of meiosis II and is the reason meiosis II resembles mitosis.

The kinetochores are __________.

sites at which microtubules attach to chromosomes The kinetochores appear to move along the spindle fiber, dragging the attached chromosomes with them.

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.

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).

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.

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

versions You will learn in a later chapter that each version of a gene is termed an allele.

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.

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

2 diploid cells; 4 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.

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.

At the end of telophase I of meiosis, as cytokinesis occurs, there are __________.

At the end of telophase I of meiosis, as cytokinesis occurs, there are __________. Each of these cells carries a haploid set of chromosomes, each consisting of two chromatids that will be separated during meiosis II.

During meiosis I, homologous chromosomes form a tetrad and crossing over occurs. What is the outcome of crossing over?

Crossing over creates 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. The genes remain organized in the same order, but a chromosome may have different versions of some genes than it did prior to crossing over.

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 The order of genes at each locus (position) along the chromosomes is the same, but there is the possibility for different forms of particular genes; for example, one chromosome may have the gene for freckles, the other may not.

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 This is the fundamental difference between these classes of tumors.

During anaphase I, __________.

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

During mitosis, the chromosomes move because _____.

they attach to a dynamic, precisely regulated mitotic spindle It is the extension and shortening of microtubules that are attached to opposite faces of chromosomes that controls chromosome movement.