Worksheets 9 & 10 BIOL LAB

How does a pair of sister chromatids differ from a single, unduplicated chromosome?

A pair of sister chromatids contains twice the DNA of a single, unduplicated chromosome.

What is the difference between mitosis and cytokinesis?

During mitosis, the nuclear material is divided into two, while cytokinesis is the division of cytoplasm forming two daughter cells.

Compare the four daughter cells with each other. How are they similar? How are they different?

Each cell contains two chromosomes, but no two cells contain the same combination of chromosomes

Describe the different ways genes are rearranged during meiosis.

First, the homologous chromosomes from each parent are randomly distributed to the two daughter cells during Meiosis I. For n pairs of homologous chromosomes there are 2n different possible arrangements, 2^2=4 in this example. For humans, that means there are 2^23=8.4x 106 possible arrangements! The second mixing of genetic materi- al occurs in crossing-over during Prophase Crossing-over results in the mixing of paternal and maternal genetic material on each chromosome.

If the chromosome number was not reduced during meiosis, what would happen during fertilization?

If the chromosome number was not reduced during meiosis, the number of chromosomes would double during fertilization. Thus there would be four pairs of chromosomes after the first generation, eight after the second, 16 after the third, and so on.

When does mitosis take place? Is mitosis taking place in your body now?

Mitosis occurs during growth and repair of tissues. Mitosis is constantly taking place in your body, particularly in skin cells since they are continually replaced. It also occurs during healing of an injured body tissue.

Why are most spinal cord or nerve tissue injuries permanent?

Nerve cells seldom undergo mitosis. Therefore, once they are damaged they cannot be replaced.

After fertilization, is the cell nucleus diploid or haploid? Explain.

The cell is diploid because each chromosome has a homologue

Use the drawings you have made to compare the cell after fertilization to the original cell before meiosis How are they different, and how are they similar?

The cell is similar in that there are two pairs of homologous chromosomes in both. The genetic material is different, however, containing some material from the original cell and some from the cell belonging to the other group (i.e.green and yellow beads)

Use the drawings you have made to compare the original cell to the two daughter cells at the end of Meiosis 1 How are the daughter cells different from the original cell?

The daughter cells are diploid, just like the original cell. But while the original cell contained two sets of homologous chromosomes, the two sets in each daughter cells are twin sister chromatids, except for regions exchanged during crossing-over.

Are the four daughter cells diploid or haploid? Explain.

The four daughter cells are haploid because they each contain half the number of chromosomes in the original cell.

Use the drawings you have made to compare the four daughter cells at the end of Meiosis Il to the two daughter cells at the end of Meiosis I and to the original cell.

The four daughter cells are haploid, while the other cells are diploid. The original genetic material has been mixed up and randomly distributed between the four cells.

In which phase of the cell cycle s a typical cell most of the time?

The most frequently seen phase (i.e.most numerous) is interphase.

What are the main differences between mitosis in animal and plant cells?

The plant cell shape-rectangular will differ from animal cell shape-oval. During telophase, plant cells begin to form a new cell wall where the metaphase plate once was. This is called the "cell plate. Animal cells begin to pinch inward at the middle during telophase. This is called the "cleavage furrow." The students also may notice that there are no centrioles in plant cells but they may be visible in animal cells.

Are the two daughter cells diploid or haploid? Explain.

The two cells are diploid because they contain two sets of similar chromosomes. These two sets are in fact near copies of each other with the exception of the regions exchanged during the crossover event.

How many daughter cells are produced by a single cell after cell division?

Two identical daughter cells are produced at the end of mitosis and cytokinesis.

What is the relationship between mitosis and cancer?

While mitosis is controlled cell division, cancer is uncontrolled cell division.