Mastering Biology Chapter 13

metaphase I

During metaphase I tetrads align along the metaphase plate.

telophase II and cytokinesis

Four haploid cells are present at the end of telophase II and cytokinesis.

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.

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

Synapsis occurs. The pairing of homologous chromosomes that only occurs during prophase I of meiosis is called synapsis.

The parent cell that enters meiosis is diploid, whereas the four daughter cells that result are haploid. Which statement correctly describes how cellular DNA content and ploidy levels change during meiosis I and meiosis II?

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. During anaphase of both meiosis I and meiosis II, the DNA content (number of copies of chromosomes) in a cell is halved. However, the ploidy level changes only when the number of unique chromosome sets in the cell changes. This occurs only in meiosis I (where separation of homologous chromosomes decreases the ploidy level from 2n to n and produces daughter cells with a single chromosome set).

metaphase II

Metaphase II is essentially the same as mitotic metaphase except that the cells are haploid.

What is the best evidence telling you whether this cell is diploid or haploid?

The cell is diploid because it contains two sets of chromosomes. Only diploid cells contain two sets of chromosomes, one maternal and one paternal. Read about diploid cells.

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

telophase I At the end of telophase I and cytokinesis, there are two haploid cells with chromosomes that consist of two sister chromatids each.

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

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

Which of the following defines a genome?

the complete set of an organism's genes

How many different combinations of maternal and paternal chromosomes can be packaged in gametes made by an organism with a diploid number of 8 (2n = 8)?

16

If the DNA content of a diploid cell in the G1 phase of the cell cycle is x, then the DNA content of the same cell at metaphase of meiosis I would be

2x

telophase I and cytokinesis

At the end of telophase I and cytokinesis there are two haploid cells.

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

Each cell has eight homologous pairs.

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

Homologous chromosomes of a pair are separated from each other.

Meiosis I is the only time that chromosomes line up by _____ pairs.

homologous

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

metaphase II Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid.

Meiosis II is similar to mitosis in that

sister chromatids separate during anaphase.

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 tetrads 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 Which of the steps takes place in both mitosis and meiosis?

3

anaphase I

During anaphase I homologous chromosomes, consisting of sister chromatids, migrate to opposite poles.

anaphase II

During anaphase II sister chromatids separate and migrate to opposite poles.

interphase

During interphase the centrosome duplicates and the chromosomes are not condensed.

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. One homologous chromosome comes from the father, and the other comes from the mother. Sister chromatids are identical copies of each other.

prophase I

Homologous chromosomes pair during prophase I

prophase II

The events of prophase II are essentially the same as those of mitotic prophase except that prophase II cells are haploid.

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. If crossing over did not occur, which of the following statements about meiosis would be true?

There would be less genetic variation among gametes.

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 anaphase I sister chromatids remain attached at their centromeres, and homologous chromosomes move to opposite poles.

During _____ sister chromatids separate.

anaphase II Anaphase II is essentially the same as mitotic anaphase except that the cell is haploid.

The _____ is the point of attachment between two duplicated chromosomes.

centromere

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

four ... haploid At the end of meiosis II there are typically 4 haploid cells.

Mitosis goes on continuously in most parts of the body, whereas meiosis takes place only in the _____.

gonads

Homologous chromosomes move toward opposite poles of a dividing cell during

meiosis I

We can see that the chromosomes are duplicated and lined up by homologous pair. That only happens at the start of _____.

meiosis I

Asexual reproduction _____.

produces offspring genetically identical to the parent Only one individual makes a genetic contribution to the offspring.

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

prophase I

Synapsis occurs during _____.

prophase I Synapsis, the pairing of homologous chromosomes, occurs during prophase I.

During _____ a spindle forms in a haploid cell.

prophase II Prophase II is essentially the same as mitotic prophase except that the cells are haploid.

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 At the end of meiosis I there are two haploid cells.