Chapter 8 (HW)

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 _____. G2 G1 M phase G0

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, M, G2, S, G1 G1, S, G2, M S, G1, G2, M G1, G2, S, M

G1, S, G2, M

What name is given to this process? gametogenesis sexual reproduction meiosis asexual reproduction fertilization

asexual reproduction

Meiosis starts with a single diploid cell and produces eight haploid cells. two diploid cells. four diploid cells. two haploid cells. four haploid cells.

four haploid cells.

Gametes are produced by _____. asexual reproduction mitosis fertilization meiosis the cell cycle

meiosis

Variation occurs when chromosomes are shuffled in _____. meiosis genetic drift mutation mitosis

meiosis

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

prophase

The correct order of events during meiosis is prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II. metaphase I, prophase I, telophase I, anaphase I, cytokinesis, meiosis II. prophase I, anaphase I, telophase I, metaphase I, meiosis II. prophase I, anaphase I, metaphase I, telophase I, meiosis II, cytokinesis. metaphase I, prophase I, anaphase I, telophase I, cytokinesis, meiosis II.

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? Metaphase I. anaphase I. meiosis II. telophase I. prophase I.

prophase I.

One version of a gene may encode __________, whereas a different version of the same gene may encode __________. white eyes; white coat white eyes; brown coat red eyes; white coat red eyes; white eyes

red eyes; white eyes

During anaphase II, __________. the cell is diploid nuclear membranes re-form sister chromatids separate and migrate toward opposite poles homologous chromosomes separate and migrate toward opposite poles

sister chromatids separate and migrate toward opposite poles

Which of these cells is (are) haploid? D B and C B A and D C and D

C and D Once meiosis I is completed, cells are haploid.

Normal human gametes carry _____ chromosomes. 46 46 pairs of 23 23 pairs of5

23

On average, what percentage of infants born to 45-year-old mothers have Down syndrome? 1% 3% 8% 10% 30%

3%

What is the difference between a benign tumor and a malignant tumor? Benign tumors are a mass of essentially abnormal cells; malignant tumors are an abnormal mass of essentially normal cells. Benign tumors will not kill you; malignant tumors will. Benign tumors do not metastasize; malignant tumors do. Benign tumors metastasize; malignant tumors do not.

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. Cancer cells continue to die at a rate that is equal to their growth. Cancer cells have inactive receptors for growth factors. Cancer cells are unable to attach to a surface and grow.

Cancer cells continuously secrete growth factors into the cell culture medium.

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. 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. The chromosome number in trisomy would be normal; in a duplication, there would be one more chromosome. In both cases there would be an extra chromosome, but in trisomy there would be three chromatids on one chromosome and in a duplication there would be two chromatids on one chromosome.

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.

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. It causes the cell to elongate. It ensures the formation of two complete nuclei around each of the chromosomes. This keeps the separate chromosomes together.

It ensures that each daughter cell receives one copy of the chromosome.

Use the graph and your knowledge of Down syndrome to select the three true statements. The number of infants born with Down syndrome increases at a steady rate from maternal age 25 to 50. The risk of having a baby with Down syndrome more than doubles for 45-year old mothers compared to 40-year old mothers. The incidence of Down syndrome in infants born to mothers under the age of 35 is less than 0.5%. Down syndrome is caused by a trisomy of chromosome 21. The largest five-year increase in the incidence of Down syndrome occurs between the maternal ages of 35 and 40.

The risk of having a baby with Down syndrome more than doubles for 45-year old mothers compared to 40-year old mothers. The incidence of Down syndrome in infants born to mothers under the age of 35 is less than 0.5%. Down syndrome is caused by a trisomy of chromosome 21.

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? These autosomal chromosomes do not contain the same type of DNA or protein that makes up chromosomes susceptible to trisomy. Trisomy for the other autosomal chromosomes is often lethal, and the affected embryos are miscarried. Trisomy for these other autosomal chromosomes occurs so rarely that it has never been documented. Trisomy for these autosomal chromosomes has no effect and therefore would never be noticed.

Trisomy for the other autosomal chromosomes is often lethal, and the affected embryos are miscarried.

During anaphase I, __________. nuclear membranes re-form homologous chromosomes separate and migrate toward opposite poles chromosomes line up in one plane sister chromatids separate and migrate toward opposite poles

homologous chromosomes separate and migrate toward opposite poles

Chromatids are _____. A. found only in aberrant chromosomes B.composed of RNA C. identical copies of each other if they are part of the same chromosome D. held together by the centrioles E. the bacterial equivalent of eukaryotic chromosomes

identical copies of each other if they are part of the same chromosome

A cell preparing to undergo meiosis duplicates its chromosomes during metaphase I. meiosis II. interphase. anaphase I. prophase I.

interphase.

A diploid organism whose somatic (nonsex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes. 8 30 64 32 16

16

In humans, the haploid number of chromosomes is 23. Independent assortment has the possibility of producing __________ different gametes. 1 million 46*2 2*23 23*2

2*23

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? All four possible embryos will be trisomic for chromosome 18. Two of the embryos will be trisomic for chromosome 18, and two will be normal. Two of the embryos will be normal, and two will contain a single copy of chromosome 18. Two of the embryos will be trisomic for chromosome 18, and two will contain a single copy of chromosome 18.

Two of the embryos will be trisomic for chromosome 18, and two will contain a single copy of chromosome 18.

Meiosis differs from mitosis in that _____ only occurs in meiosis. the formation of a spindle cytokinesis crossing over the fragmentation of the nuclear envelope

crossing over

A cell is treated with a drug that prevents the formation of vesicles. Which of the following processes depends on the formation of vesicles and would therefore be blocked? alignment of eukaryotic chromosomes at the metaphase plate cytokinesis in an animal cell separation of eukaryotic chromosomes at anaphase cytokinesis in a plant cell

cytokinesis in a plant cell

During prophase I of meiosis, chromosome pairs are positioned in the middle of the cell. the homologous chromosomes separate and move towards opposite poles. there are two daughter cells, each with 23 chromosomes. there are four haploid daughter cells. homologous chromosomes stick together in pairs.

homologous chromosomes stick together in pairs.

When we say that an organism is haploid, we mean that _____. its cells each have one set of chromosomes Its cells have one half of a chromosome its cells each have one chromosome its cells each have two sets of chromosomes

its cells each have one set of chromosomes

Polyploidy is involved in which of the following examples? A normal watermelon has 22 chromosomes but seedless watermelons have 33 chromosomes. XYY males XO females Some plants alternate between haploid and diploid phases.

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

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? There is a mechanism to keep only two X chromosomes functional, regardless of the total number. Only one copy of the X chromosome is functional within any given cell, regardless of the total number of X chromosomes. The X chromosome does not carry any genes. The number of X chromosomes is always balanced by the number of Y chromosomes.

Only one copy of the X chromosome is functional within any given cell, regardless of the total number of X chromosomes.