Mastering Biology CH 13 homework

Homologous pairs of chromosomes are lined up independently of other such pairs during _____.

Metaphase I

The following statements discuss events associated with meiosis. Determine which statements are true and which are false. Drag "True" or "False" to the end of each statement

-The second division of meiosis reduces the number of chromosomes in each cell by half. False -In meiosis II, the daughter cells from meiosis I undergo a very similar division to mitosis. True -The first division of meiosis reduces the number of chromosomes in each cell by half. True -Crossing over and synapsis occur after the homologous chromosomes separate in meiosis I. False -Meiosis occurs in both somatic (body) cells and sex cells. False

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. Drag the labels to fill in the targets beneath each diagram of a cell. Note that the diagrams are in no particular order.Drag labels of Group 1 to identify the stage of meiosis depicted in each diagram.Drag labels of Group 2 to identify whether the configuration of the chromosomes related to crossing over is possible or not.

Which phase of mitosis is represented in each cell? A. anaphase II B. metaphase II C. prophase I D. metaphase I Are the events or results of crossing over possible as shown in each cell? E. yes F. no G. no H. yes

Imagine that I've taken a snapshot of the chromosomes in a hypothetical cell. Part of the snapshot looks like this. What stage of the lifecycle must the cell be in?

The start of meiosis I

You may remember this shot from the video podcast. Here I am representing a duplicated chromosome. What structure is represented at my waist? Where am I joined to my twin?

centromere

Imagine you found a hypothetical organism. You examine one of its gametes and you see that it contains 5 chromosomes. How many chromosomes will one of its body cells contain just before mitosis begins?

10

Drag the labels from the left to their correct locations in the concept map on the right.

A. Chromatin B. Genes C. Chromosomes D. Genome E. Traits F. Locus G. Gametes

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. Drag the labels to their appropriate targets to correctly identify the various chromosome structures. Labels can be used more than once.

A. Non-homologous chromosomes B. Sister chromatids C. Homologous chromosomes D. Centromere E. Nonsister chromatids F. Homologous chromosomes G. Sister chromatids

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.) The cells below show the eight possible combinations of chromosomes that the daughter cells of meiosis II can receive. Sort each daughter cell into the appropriate bin depending on which arrangement at metaphase I would create it.

Arrangement 1: 3 and 8 Arrangement 2: 1 and 5 Arrangement 3: 6 and 2 Arrangement 4: 4 and 7

Which of these gametes contains one or more recombinant chromosomes?

B and C

Which of these gametes contain one or more recombinant chromosomes?

B, C, F, and G

Two sister chromatids are joined at the centromere prior to meiosis. Which statement is correct?

Barring mutation, the two sister chromatids must be identical.

Which processes lead to most genetic variation in sexually reproducing organisms? Select all that apply.

Crossing over Independent assortment of chromosomes in meiosis Random fertilization

Can you recognize the eight stages of meiosis based on the location and behavior of the chromosomes? Drag the diagrams of the stages of meiosis onto the targets so that the four stages of meiosis I and the four stages of meiosis II are in the proper sequence from left to right. (Note that only one of the two daughter cells is shown for meiosis II.)

Image provides answers

Can you match these prefixes, suffixes, and word roots with their definitions?

change, after: meta- different, other: hetero- milk: lact- blood: hem- (or hemato-) enzyme: -ase within: intra- three: tri- one-half: semi- across: trans-

Human gametes are produced by _____.

meiosis

If you look through a microscope and see a cell with chromosomes lined up like this, two by two, what stage of cellular reproduction must you be looking at?

meiosis I only

Of the two processes that we learned about which is going on in my hand right now?

mitosis

Can you match these prefixes, suffixes, and word roots with their definitions?

to love: -phil (or philo-) difficult, painful: dys- of neither gender or type: neutr- to: ad- with or together with: co- against: anti- not: non- change, turn, move: trop- (or -tropic) from, out of, remove: de- many: poly-

Normal human gametes carry _____ chromosomes.

23

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

16

In human gamete production there is an average of _____ crossover events per chromosome pair.

2-3

Which of these cells is (are) haploid?

C and D

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.

Identify all possible products of meiosis in plant and animal life cycles. Select all that apply.

Gametes (sperm and eggs) Spores

Mitosis can occur in both haploid and diploid cells, but meiosis can only occur in diploid cells. Why?

Meiosis produces daughter cells with half the number of chromosome sets of the parent cell; therefore, the parent cell must be diploid.

The video compares the key similarities and differences between mitosis and meiosis. Determine which events occur in mitosis, meiosis, or in both mitosis and meiosis. Sort each event to the appropriate bin.

Mitosis: -End result is two diploid cells that are genetically identical to each other and the parent cell. -A single division occurs, separating sister chromatids. -Duplicated chromosomes line up individually on the metaphase plate in a diploid cell. Meiosis: -Homologous chromosomes pair up and form chiasmata. -End result is four haploid cells that are genetically different from each other and the parent cell. -Daughter cells contain recombinant chromosomes. -The first division separates homologous pairs; the second division separates sister chromatids. -Homologous pairs of chromosomes line up on the metaphase plate. Both mitosis and meiosis: -Process starts with a diploid cell. -Chromosomes duplicate during interphase.

Crossing over, resulting in an increase in genetic variation, occurs between _____.

Nonsister chromatids of homologous chromosomes

This chromosome has two chromatids, joined at the centromere. What process led to the formation of the two chromatids?

The two chromatids were formed by duplication of a chromosome.

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? Select all that apply.

There would be less genetic variation among gametes.

Meiosis guarantees that in a sexual life cycle, offspring will inherit one complete set of chromosomes (and their associated genes and traits) from each parent. The transmission of traits from parents to offspring is called heredity. Another important aspect of meiosis and the sexual life cycle is the role these processes play in contributing to genetic variation. Although offspring often resemble their parents, they are genetically different from both of their parents and from one another. The degree of variation may be tremendous. The following processes are associated with meiosis and the sexual life cycle: -DNA replication before meiosis -crossing over -chromosome alignment in metaphase I and separation in anaphase I -chromosome alignment in metaphase II and separation in anaphase II -fertilization Sort each process into the appropriate bin according to whether it contributes to heredity only, genetic variation only, or both. (Note that a bin may be left empty.)

Heredity only: -none Genetic variation: -none Both: -DNA replication -Crossing over -Metaphase I to anaphase I -Metaphase II to anaphase II -Fertilization

In the life cycle of an organism, meiosis is paired with the process of fertilization. Understanding the life cycle of an organism is the key to understanding how sexual reproduction ensures the inheritance of traits from both parents and also introduces genetic variation. Complete the diagram to show the life cycle of a typical animal. Follow these steps: Drag labels of Group 1 to identify each stage of the life cycle. Drag labels of Group 2 to identify the ploidy level at each stage. Drag labels of Group 3 to identify the process by which each stage occurs. Labels can be used once, more than once, or not at all.

A. 2n B. 2n C. meiosis D. meiosis E. n F. egg G. sperm H. n I. fertilization J. 2n K. zygote L. mitosis M. 2n N. meiosis O. n P. egg