Mastering Ch.13

PARTA - The stages of meiosis 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.)

PART B - Crossing over 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 the blue labels to the blue targets to identify the stage of meiosis depicted in each diagram. Drag the pink labels to the pink targets to identify whether the configuration of the chromosomes related to crossing over is possible or not.

PART C - Changes in ploidy and DNA content during meiosis 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?

PART A - Meiosis terminology Drag the labels from the left to their correct locations in the concept map on the right.

PART B - Interactions among chromosomes 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.

PART C - Animal life cycles 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: 1. First, drag blue labels onto blue targets only to identify each stage of the life cycle. 2. Next, drag pink labels onto pink targets only to identify the process by which each stage occurs. 3. Then, drag white labels onto white targets only to identify the ploidy level at each stage. Labels can be used once, more than once, or not at all.

PART A - Processes that determine heredity and contribute to genetic variation 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.)

PART B - Independent assortment and genetic variation 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.

PART C - Crossing over and genetic variation 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.

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

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

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

Look at the cell in the figure. Based on this figure, which of the following statements is true?

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

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

You may remember this shot from the video pod cast. Here I am representing a duplicated chromosome. What structure is represented by my waist, where I am joined?

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?

What stage of the life cycle must this cell be in?

Independent assortment of chromosomes during meiosis is a result of