13 Biology

Gray seed color in peas is dominant to white. Assume that Mendel conducted a series of experiments where plants with gray seeds were crossed among themselves, and the following progeny were produced: 302 gray and 98 white. (a) What is the most probable genotype of each parent? (b) Based on your answer in (a) above, what genotypic and phenotypic ratios are expected in these progeny? (Assume the following symbols: G = gray and g = white.)

(a) Gg × Gg; (b) genotypic = 1:2:1, phenotypic = 3:1

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

- Spores - Gametes (sperm and eggs)

Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes?

100%

Part L - Applying the results Given the fact that 1 fg of DNA = 9.78 × 105 base pairs (on average), you can convert the amount of DNA per cell to the length of DNA in numbers of base pairs. Millions of base pairs (Mb) is the standard unit for expressing genome size. Calculate the approximate number of base pairs of DNA in the haploid yeast genome.

12 Mb (12 x 106 base pairs )

Part I How many femtograms of DNA are present in a cell at the end of meiosis II?

12 fg

Part K Based on this data, how much DNA is present in a gamete of Saccharomyces cerevisiae?

12 fg

Part C Now that you have determined which variable goes on each axis, the graph can be constructed. An effective graph marks off the axes with just enough evenly spaced tick marks to accommodate the full set of data. Assuming that the x-axis tick marks will be separated by 1.0 units (0, 1.0, 2.0, and so on), what is the largest value that should appear on the x-axis?

14.0

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

Part M Given the fact that 1 fg of DNA = 9.78 × 105 base pairs (on average), you can estimate the rate of DNA synthesis in Saccharomyces cerevisiae. Approximately how many base pairs per minute were synthesized during the S phase of these yeast cells?

200,000 (2.0 × 105) base pairs per minute

Part F - Using data from the graph Most of the yeast cells in the culture were in G1 of the cell cycle before being moved to the nutrient-poor medium to induce meiosis. Select Figure 2 in the drop-down menu above the table (Figure 2) . A graphical version of the data (similar to the one you just made) is shown. How many femtograms of DNA are there in a yeast cell in G1? Estimate this value from the data in the graph.

24 fg

Part H How many femtograms of DNA are present in a cell at the end of meiosis I?

24 fg

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

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

44 autosomes and 2 sex chromosomes

Part G How many femtograms of DNA are present in a cell in G2?

48 fg

Part D Assuming that the y-axis tick marks will be separated by 5 units (0, 5, 10, and so on), what is the largest value that should appear on the y-axis?

55.0

What do we mean when we use the terms monohybrid cross and dihybrid cross?

A dihybrid cross involves organisms that are heterozygous for two characters and a monohybrid cross involves only one.

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: First, drag blue labels onto blue targets only to identify each stage of the life cycle. Next, drag pink labels onto pink targets only to identify the process by which each stage occurs. 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.

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

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.

A. anaphase 2 B. metaphase 2 C. prophase 1 D. metaphase 1 E. yes F. no G. no H. yes

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

A. chromatin G. genes C. chromosomes D. genome E. traits F. locus G. gametes

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.

A. non-homolougous chromosomes B. sister chromatids C. homologous chromosomes D. centromere E. non-sister chromatids F homologous chromosomes G. sister chromatids

A woman who has blood type A positive has a daughter who is type O positive and a son who is type B negative. Rh positive is a trait that shows simple dominance over Rh negative. Which of the following is a possible phenotype for the father?

B positive

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

Barring mutation, the two sister chromatids must be identical.

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?

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.

How many unique gametes could be produced through independent assortment by an individual with the genotype AaBbCCDdEE?

G

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.

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

Synapsis occurs.

Part A: 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.

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

The first three answers are correct.

Part A: 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.

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.

There would be less genetic variation among gametes.

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

This cell is diploid.

SRY is best described as _____

a gene region present on the Y chromosome that triggers male development

A human cell containing 22 autosomes and a Y chromosome is

a sperm.

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

across: trans- three: tri- within: intra- change: meta- enzyme: -ase blood: hem- one-half: semi- different: hetero- milk: lact-

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

against: anti- to: ad- from: de- many: poly- difficult: dys- to love: -phil change: trop- not: non- with: co- neither gender or type: neutr-

Part B What variable's response to the independent variable was measured by the researchers, and what are the units for this variable?

average amount of DNA per cell, in femtograms

Part J - Interpreting the graph Select Figure 3 in the drop-down menu (Figure 3) . The graph with labels indicating the different phases of the meiotic cell cycle (MI = meiosis I; MII = meiosis II) is shown. Think carefully about the point on the graph where the line at the highest value begins to slope downward, indicated by the red arrow. What specific point of meiosis does this "corner" represent?

cytokinesis

Heritable variation is required for which of the following?

evolution

Part E Use the data at left to make a line graph. To create the graph, first click on "add graph" and select the label "Amount of DNA per Cell Over Time."

graph the points.

Part A - 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.)

http://biology-forums.com/index.php?topic=88873.0 squint at the thumbnails

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.) Four diagrams showing four equally probable arrangements of three homologous pairs at metaphase I. In arrangement 1, the pairs are from top to bottom: red-blue, red-blue, red-blue. In arrangement 2, the pairs are from top to bottom: red-blue, blue-red, blue-red. In arrangement 3, the pairs are from top to bottom: red-blue, blue-red, red-blue. In arrangement 4, the pairs are from top to bottom: red-blue, red-blue, blue-red. 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.

http://biology-forums.com/index.php?topic=92647.0 squint at the thumbnail

The shuffling of chromosomes that occurs during both fertilization and _____ can lead to genetic variation.

meiosis

Homologous chromosomes move toward opposite poles of a dividing cell during

meiosis I.

Which life cycle stage is found in plants but not animals?

multicellular haploid

Asexual reproduction _____.

produces offspring genetically identical to the parent

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.)

put all the answers in "both"

Meiosis II is similar to mitosis in that

sister chromatids separate during anaphase.

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

sporophyte

What is crossing over?

the exchange of homologous portions of nonsister chromatids

Part A - Making a graph with the data To see patterns in the data from a time-course experiment like this, it is helpful to plot the data on a line graph. But first, you must determine which variable should go on each axis of the graph. What variable did the researchers intentionally vary in the experiment, and what are the units for this variable? (This is the independent variable.)

time after induction, in hours

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

two diploid cells ... four haploid cells

If we continued to follow the cell lineage from question 5, then the DNA content of a single cell at metaphase of meiosis II would be

x