MasteringBiology Chapter 9

In a typical human body cell, how many sex chromosomes are there? A. 2 B. 1 C. 46 D. 23

A. 2

_____ is a carcinogen that promotes colon cancer. A. fat B. UV light C. estrogen D. a virus E. testosterone

A. fat. A diet high in fat increases the risk of both colon and breast cancer.

In human gamete production there is an average of _____ crossover events per chromosome pair. A. 5-6 B. 2-3 C. 9-10 D. 0-1 E. 10+

B. 2-3. These crossover events increase the genetic variation among gametes.

The sister chromatids separate and begin moving toward opposite poles of the cell during which phase of mitosis? A. Metaphase. B. Anaphase. C. Interphase. D. Telophase. E. Prophase.

B. Anaphase. Sister chromatids separate and start their migration toward opposite poles during anaphase.

The chromosomes line up in the center of the cell during which phase of mitosis? A. Prophase. B. Metaphase. C. Anaphase. D. Interphase. E. Telophase

B. Metaphase. Metaphase occurs in the middle of mitosis, when the chromosomes line up in the middle of the cell.

Which of the following is the most important for generating the most genetic variability in a species? A. recombination B. ability to fuse haploid gametes to form a new individual C. crossing over D. more than one chromosome E. asexual reproduction F. mitosis

B. ability to fuse haploid gametes to form a new individual. The ability to combine different sets of alleles into one individual is most important to generating diversity.

At the end of the mitotic (M) phase, the cytoplasm divides in a process called _________________. A. meiosis B. cytokinesis C. telophase D. condensation E. replication

B. cytokinesis. Cytokinesis is the division of the cytoplasm that occurs in conjunction with telophase, the last phase in mitosis.

All the genes in a population are that population's _____. A. phenotype B. gene pool C. genotype D. fitness E. Hardy-Weinberg

B. gene pool. All the alleles of all the genes of a population make up a gene pool.

Which of these phases of the cell cycle is most similar between a cell that will divide by mitosis and one that will divide by meiosis? A. metaphase B. interphase C. anaphase D. prophase E. telophase

B. interphase. In either case, the DNA must be duplicated in order to divide the cells.

Homologous pairs of chromosomes are lined up independently of other such pairs during _____. A. anaphase I B. metaphase I C. prophase II D. telophase II E. metaphase II

B. metaphase I.

Every few years a giant axe chops off the head of every person who is over 6 feet tall. How will this affect the human population? A. The mutation rate will increase. B. Gene flow will increase. C. Alleles that promote "tallness" will decrease in frequency. D. Genetic drift will play less of a role in the evolution of humans. E. It will increase in number since shorter people use fewer resources than taller people

C. Alleles that promote "tallness" will decrease in frequency. A reduction in "tallness" alleles is the change expected as a result of this type of selection.

Meiosis starts with a single diploid cell and produces A. two haploid cells B. two diploid cells C. four haploid cells. D. four diploid cells E. eight haploid cells

C. four haploid cells; Meiosis produces four haploid cells.

Which of these individuals is a homozygous genotype? A. Gg B. Aa C. aG D. AA E. AG

D. AA. When both of the alleles of a given gene pair are the same, the individual is homozygous for that gene.

The chromosomes arrive at the poles and nuclear envelopes form during which phase of mitosis? A. Metaphase. B. Prophase. C. Anaphase. D. Telophase. E. Interphase

D. 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.

During which phase of the eukaryotic cell cycle does DNA and chromosome replication occur? A. cytokinesis B. the mitotic phase C. the G1 phase of interphase D. the S phase of interphase

D. The S phase of interphase

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

E. homologous chromosomes stick together in pairs. Homologous chromosomes stick together in pairs during prophase I.

Crossing over, resulting in an increase in genetic variation, occurs between _____. A. sex cells and somatic cells B. sister chromatids of nonhomologous chromosomes C. sister chromatids of homologous chromosomes D. nonsister chromatids of nonhomologous chromosomes E. nonsister chromatids of homologous chromosomes

E. nonsister chromatids of homologous chromosomes. This process produces chromosomes containing genes inherited from both parents.

A mutation occurs when _____. A. there is a change in the DNA sequence of a gene B. population sizes are small C. individuals enter a population D. individuals leave a population E. some individuals leave more offspring than other individuals

A. there is a change in the DNA sequence of a gene.

In a typical human body cell, how many chromosomes are there? A. 2 B. 23 C. 46 D. 1

C. 46

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

A. interphase; Chromosomes are duplicated during interphase.

Meiotic cell division occurs in the ________ and results in the production of ________. A. reproductive tissues; gametes. B. testes and ovaries; diploid cells. C. body cells; daughter cells D. body cells; parent cells

A. reproductive tissues; gametes

The correct order of events during meiosis is: A. metaphase I, prophase I, telophase I, anaphase I, cytokinesis, meiosis II. B. prophase I, anaphase I, telophase I, metaphase I, meiosis II. C. metaphase I, prophase I, anaphase I, telophase I, cytokinesis, meiosis II. D. prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II. E. prophase I, anaphase I, metaphase I, telophase I, meiosis II, cytokinesis.

D. prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II. Meiosis starts with prophase I and continues with metaphase I, anaphase I, telophase I, and cytokinesis. This is followed by meiosis II.

How are homologous chromosomes defined? A. Homologous chromosomes contain the same genes, but may contain different alleles. B. Homologous chromosomes contain the same alleles, but each allele is at a different locus. C. Homologous chromosomes contain the same genes, but each gene is at a different locus. D. Homologous chromosomes contain the same alleles, but may contain different genes. E. Homologous chromosomes contain the same genes and the same alleles.

A. Homologous chromosomes contain the same genes, but may contain different alleles. Homologous chromosomes have identical genes, but may have different varieties of that gene (brown hair vs. black hair).

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? A. telophase I. B. prophase I. C. meiosis II. D. anaphase I. E. Metaphase I.

B. prophase I. Segments of nonsister chromatids trade places during prophase I, resulting in recombination.

Genetic drift is a process based on _____. A. emigration B. the role of chance C. mutation D. immigration E. differential reproductive success correlated to the relationship between a phenotype and the environment

B. the role of chance. Genetic drift requires a small sample size.

When a cell divides via asexual reproduction: A. each daughter cell receives exactly half the genetic information in the parent cell. B. each daughter cell receives the same amount of genetic information that was in the parent cell, but it has been altered. C. each daughter cell receives a nearly perfect copy of the parent cell's genetic information. D. the genetic information is randomly parceled out to the daughter cells.

C. each daughter cell receives a nearly perfect copy of the parent cell's genetic information.

The ease with which humans travel across the globe is likely to increase _____. A. natural selection B. genetic drift C. mutation D. gene flow E. all of these

D. gene flow. When people travel or migrate, they take their alleles with them.

The centrosomes move away from each other and the nuclear envelope breaks up during which phase of mitosis? A. Interphase. B. Telophase. C. Metaphase. D. Anaphase. E. Prophase

E. Prophase. Prophase is the first phase of mitosis, when the centrosomes begin moving toward opposite poles and the nuclear envelope breaks up.

What must happen before a cell can begin mitosis? A. A mitotic spindle must form. B. The nucleus must divide in two. C. The sister chromatids must be separated. D. The nuclear envelope must break up. E. The chromosomes must be duplicated

E. The chromosomes must be duplicated. Before mitosis can begin, the chromosomes, or genetic material, must be copied, which occurs during interphase.

Which of these is NOT a carcinogen? A. cigarette smoke B. UV light C. fat D. testosterone E. all of the above are carcinogens

E. all of the above are carcinogens. All of these substances can cause cancer.

Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans. A. natural selection B. mutation C. gene flow D. disease E. genetic drift

E. genetic drift. Modern travel and migration decreases the chances of there being a small, isolated population.