Chapter 10 Mastering Biology

If a horticulturist breeding gardenias succeeds in having a single plant with a particularly desirable set of traits, which of the following would be her most probable and efficient route to establishing a line of such plants?

Clone the plant asexually to produce an identical one.

Which processes lead to most genetic variation in sexually reproducing organisms?

Crossing over independent assortment of chromosomes in meiosisrandom fertilization

The parent cell that enters meiosis is diploid, whereas the four daughter cells that result are haploid.

DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II.

Which of the following happens at the conclusion of meiosis I?

Homologous chromosomes of a pair are separated from each other.

For the following question, match the key event of meiosis with the stages listed below. I. Prophase I V. Prophase II II. Metaphase I VI. Metaphase II III. Anaphase I VII. Anaphase II IV. Telophase I VIII. Telophase II

I only

For the following question, match the key event of meiosis with the stages listed below. I. Prophase I V. Prophase II II. Metaphase I VI. Metaphase II III. Anaphase I VII. Anaphase II IV. Telophase I VIII. Telophase II

II

Eukaryotic sexual life cycles show tremendous variation. Of the following elements, which do all sexual life cycles have in common? I. Alternation of generations II. Meiosis III. Fertilization IV. Gametes V. Spores

II, III, and IV

Which of the following is a true statement about sexual vs. asexual reproduction?

In sexual reproduction, individuals transmit 50% of their genes to each of their offspring.

If a cell has completed the first meiotic division and is just beginning meiosis II, which of the following is an appropriate description of its contents?

It has half the amount of DNA as the cell that began meiosis.

A given organism has 46 chromosomes in its karyotype. We can therefore conclude which of the following?

Its gametes must have 23 chromosomes.

When homologous chromosomes cross over, what occurs?

Specific proteins break the two strands of nonsister chromatids and re-join them.

Which of the following occurs during meiosis but not during mitosis?

Synapsis occurs.

For what purpose(s) might a karyotype be prepared?

The first three answers are correct.

The karyotype of one species of primate has 48 chromosomes. In a particular female, cell division goes awry and she produces one of her eggs with an extra chromosome (25). The most probable source of this error would be a mistake in which of the following?

either anaphase I or II

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

four ... haploid

Referring to a plant's sexual life cycle, which of the following terms describes the process that leads directly to the formation of gametes?

gametophyte mitosis

After telophase I of meiosis, the chromosomal makeup of each daughter cell is

haploid, and the chromosomes are each composed of two chromatids.

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

metaphase II

Independent assortment of chromosomes is a result of

the random and independent way in which each pair of homologous chromosomes lines up at the metaphase plate during meiosis I.

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

two ... haploid

Mitosis results in the formation of how many cells; meiosis results in the formation of how many cells?

two diploid cells ... four haploid cells

A pair of homologous chromosomes includes which of the following sets of DNA strands?

two sister chromatids that have synapsed

Which of the following defines a genome?

the complete set of an organism's genes

What is crossing over?

the exchange of homologous portions of nonsister chromatids

Mitosis is commonly found in all of the following except

a haploid animal cell.

Which of the following can utilize both mitosis and meiosis in the correct circumstances?

a plantlike protist

Experiments with cohesins have found that

cohesins are protected from cleavage at the centromere during meiosis I.

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

16

Normal human gametes carry _____ chromosomes.

23

The following question refers to the essential steps in meiosis described below. 1. Formation of four new nuclei, each with half the chromosomes present in the parental nucleus 2. Alignment of homologous chromosomes at the metaphase plate 3. Separation of sister chromatids 4. Separation of the homologs; no uncoupling of the centromere 5. Synapsis; chromosomes moving to the middle of the cell in pairs

3

What number and types of chromosomes are found in a human somatic cell?

44 autosomes and 2 sex chromosomes

A triploid cell contains three sets of chromosomes. If a cell of a usually diploid species with 42 chromosomes per cell is triploid, this cell would be expected to have which of the following?

63 chromosomes in 21 sets of 3

Which of the following is an example of alternation of generations?

A diploid plant (sporophyte) produces, by meiosis, a spore that gives rise to a multicellular, haploid pollen grain (gametophyte).

Consider a diploid cell where 2n = 6. During metaphase I of meiosis, as the pairs of homologous chromosomes line up on the metaphase plate, each pair may orient with its maternal or paternal homolog closer to a given pole. There are four equally probable arrangements of the homologous pairs at metaphase I. (Note that this problem assumes that no crossing over has occurred.)

Arrangement 1) 3 & 8 Arrangement 2) 1 & 5 Arrangement 3) 2 & 6 Arrangement 4) 4 & 7

Which of these statements is false?

At sexual maturity, ovaries and testes produce diploid gametes by meiosis.

Which of these gametes contains one or more recombinant chromosomes?

B and C

Which of these cells is (are) haploid?

C and D

To view and analyze human chromosomes in a dividing cell, which of the following is (are) required?

DNA staining and a light microscope

Which of the following is true of a species that has a chromosome number of 2n = 16?

Each cell has eight homologous pairs.

The somatic cells of a privet shrub each contain 46 chromosomes. To be as different as they are from human cells, which have the same number of chromosomes, which of the following must be true?

Genes of privet chromosomes are significantly different than those in humans.

How are sister chromatids and homologous chromosomes different from each other?

Homologous chromosomes contain the same gene loci but may have different alleles of a particular gene. Sister chromatids are identical copies of each other produced during DNA replication.

Independent assortment of chromosomes occurs.

The statement is true for meiosis I only.

Chromatids are separated from each other.

The statement is true for mitosis and meiosis II.

Assume that an organism exists in which crossing over does not occur, but that all other processes associated with meiosis occur normally. Consider how the absence of crossing over would affect the outcome of meiosis.

There would be less genetic variation among gametes.

How do cells at the completion of meiosis compare with cells that have replicated their DNA and are just about to begin meiosis?

They have half the number of chromosomes and one-fourth the amount of DNA.

Whether during mitosis or meiosis, sister chromatids are held together by proteins referred to as cohesins. Such molecules must have which of the following properties?

They must be removed before sister chromatids or homologous chromosomes can separate.

For the following question, match the key event of meiosis with the stages listed below. I. Prophase I V. Prophase II II. Metaphase I VI. Metaphase II III. Anaphase I VII. Anaphase II IV. Telophase I VIII. Telophase II

VII

Which of the following best describes a karyotype?

a display of each of the chromosomes of a single cell

Crossing over plays a critical role in increasing the genetic variation among offspring of sexual reproduction. It is important to understand how crossing over occurs and its consequences in meiosis. Look carefully at the diagrams depicting different stages in meiosis in a cell where 2n = 6. Assume that the red chromosomes are of maternal origin and the blue chromosomes are of paternal origin.

a. anaphase II b. metaphase II c. prophase I d. metaphase I e. yes f. no g. no h. yes

This diagram shows a diploid nucleus (2n=8) in which chromosome replication has occurred in preparation for mitosis (top) and meiosis (bottom). The nucleus at top right is now in prophase of mitosis; the nucleus at bottom right is now in prophase I of meiosis.

a. non-homologous chromosomes b. sister chromatids c. homologous chromosomes f. homologous chromosomes g. sister chromatids e. nonsister chromatids

For a species with a haploid number of 23 chromosomes, how many different combinations of maternal and paternal chromosomes are possible for the gametes?

about 8 million

Which of the following might result in a human zygote with 45 chromosomes?

an error in either egg or sperm meiotic anaphase

Homologous chromosomes migrate to opposite poles during _____.

anaphase I

During _____ sister chromatids separate.

anaphase II

Which of the following best describes the frequency of crossing over in mammals?

at least 1-2 per chromosome pair

If an organism is diploid and a certain gene found in the organism has 18 known alleles (variants), then any given organism of that species can/must have which of the following?

at most, 2 alleles for that gene

Which of these is a way that the sexual life cycle increases genetic variation in a species?

by allowing crossing over

The human X and Y chromosomes

include genes that determine an individual's sex.

When does the synaptonemal complex disappear?

late prophase of meiosis I

In a human karyotype, chromosomes are arranged in 23 pairs. If we choose one of these pairs, such as pair 14, which of the following do the two chromosomes of the pair have in common?

length, centromere position, staining pattern, and traits coded for by their genes

Genetic variation occurs when chromosomes are shuffled in fertilization and what other process?.

meiosis

Heritable variation is required for which of the following?

meiosis

Human gametes are produced by _____.

meiosis

Which is the smallest unit containing the entire human genome?

one human somatic cell

Which of these is a karyotype?

organized images of a cells chromosomes

To visualize and identify meiotic cells at metaphase with a microscope, what would you look for?

pairs of homologous chromosomes all aligned at the cell's center

Asexual reproduction _____.

produces offspring genetically identical to the parent

Synapsis occurs during _____.

prophase I

When we see chiasmata under a microscope, that lets us know which of the following has occurred?

prophase I

During _____ a spindle forms in a haploid cell.

prophase II

In alternation of generations, what is the diploid stage of a plant that follows fertilization called?

sporophyte

Which of the following occurs in meiosis but not in mitosis?

synapsis of chromosomes

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